<I>Meoma Ventricosa</I>

CONTRIBUTIONS TO THE BIOLOGY OF MEOMA VENTRICOSA (ECHINOIDEA: SPATANGOIDA)1

RICHARD H. CHESHER2 Museum of Comparative Zoology, Harvard University

ABSTRACT The biology of Meoma ventricosa (Echinoidea; Spatangoida) is described on the basis of a two-year study conducted in Florida, the Bahama Islands, Panama, and Colombia. The habitat, behavior, food and feeding, growth, reproduction, predators, parasites, commensals, abnormalities, internal anatomy, and relation to the substrate of this large, abundant echinoid are discussed.

INTRODUCTION Meoma ventricosa was described by Lamarck in 1816 but until Kier & Grant (] 965) published data on its distribution and behavior, nothing was known about the ecology of this large and abundant animal. M. ventricosa is a member of the largest and most successful order of sea-urchins, the Spatangoida. Spatangoids live in the mud and sand bottoms of all oceans and range in depth from the intertidal zone to about 5000 meters. The literature and systematics of the group are in excellent order, having been summarized by Mortensen (1950, 1951). The fossil history of spatangoids is perhaps superior to that of any other echinoderm group. One of the few known examples of long-term, continuous evolution is that of a spatangoid from the Chalk of England (Kermack, 1954; Nichols, 1959). In spite of such impressive attributes, very little is known about spatangoid biology. What data is available shows this to be a rewarding area of study. Moore (1936), Nichols (1959, 1962), Buchanan (1966, 1967), Brattstrom (1946), and Vasseur & Carlsen (1949) have studied ecological aspects of European spatangoids, and Moore & Lopez (1966), Chesher ( 1963), and Kier & Grant (1965) have studied ecological aspects of some tropical spatangoids. One of the major difficulties in studying spatangoids has been their habit of burrowing, which makes them difficult to find and capture. This is particularly true in shallow water, where maneuvering is dangerous for ships with adequate dredging facilities. The development and popularization of free diving apparatus has opened the way for intensive ecological studies in these and other areas which are relatively inaccessible from the surface (Riedl, 1967). M. ventricosa (Fig. 2) is a burrowing sea-urchin common to the coral

1Contribution No. 986 from the Institute of Marine Sciences, University of Miami. " Present address: Department of Biology, College of Guam, Agana, Guam. 1969J Chesher: Biology of Meoma ventricosa 73 reef areas of the West Indies; it is one of the largest and most accessible of the sand-dwelling, tropical spatangoids. Large populations found in Florida, the Bahamas, and Panama provide an excellent opportunity to examine the urchins in their natural habitat. Using various diving techniques, which ranged from snorkeling to night diving with small submarines, populations of M. ventricosa were examined from Fort Lauderdale to Key West along the Florida coast, and in a variety of locations in the Bahama Islands, in Panama, and in eastern Colombia. Monthly observations and collections were made near Molasses and Alligator reefs in the Florida Keys. Distribution, behavior, reproduction, growth rates, and ecological parameters were examined in the field. Morphology, internal anatomy, and details of behavior were studied in the laboratories of the Institute of Marine Sciences, Miami, Florida. The study began in 1964 and continued through the summer of 1966.

MATERIALS AND METHODS Populations of M. ventricosa were studied from Santa Marta, Colombia; Isla Grande, Panama; Key West, Alligator Reef, Molasses Reef, Ajax Reef, Triumph Reef, Fowey Rocks reef, and Fort Lauderdale along the Florida coast; and Bimini, Grand Bahama, Abaco, Andros, the Berry Is- lands, New Providence, and the Exuma Islands in the Bahama Islands. Preserved specimens were examined from Bermuda, the Gulf of Mexico, Puerto Rico, and other areas in the Caribbean. Skin-diving and scuba-diving techniques were used to examine the populations in situ. Diving operations were conducted both during the day and at night in depths from the intertidal zone to 60 meters. The distribution of the populations of M. ventricosa in Florida was observed in local areas at night from a towed submarine. Adult urchins were collected simply by picking them up by hand, but young urchins posed a problem, as they leave no trace on the surface of the sand and do not emerge from the sand at night as do the adults. Three methods proved successful for finding them. Many young specimens were found living under coral slabs behind the shallow reef areas. The coral slabs were overturned, and the sand washed away by "fanning" the area by hand or by flipper. Young specimens were excavated from the grass areas with a small air-lift dredge. For portability and convenience, an air- lift was designed to operate from a tank of compressed air. The unit (Fig. 1,A) was made from a 3-meter section of plastic tubing, 6.5 cm in diameter, of the type used in taking deep-sea cores. A fine-mesh net bag was clamped onto one end of the tube. Air was introduced to the other end of the tube via a high-pressure hose and valve assembly attached to a scuba tank. The valve controlled the flow of air and thus the amount of material lifted and the length of time the unit could be used. When in use, 74 Bulletin of Marine Science [19(1 )

FIGURE I.-A, portable air-lift dredge for capturing small specimens of burrowing animals. (n, net bag to retain specimens; h, clamp; p, plastic tube, 3 meters long, 6.5 cm diameter; i, intake end; c, collar to provide an even flow of air into the intake end of the dredge; v, valve controlling the air flow; t, high pressure rubber hose; y, yoke to fasten hose to scuba tank.)-B, measuring board for tagging urchins underwater. Construction is of %-inch clear Plexiglas. Ca, movable arm; I, pencil; 95, the tag number on the urchin and marked on the board; s, pencil sharpener.) 1969] Chesher: Biology of Meoma ventricosa 75 the end with the net was directly above the diver and the end which re- ceived the flow of air was held next to the sand. The dredge sucked up large amounts of sand and could operate continuously for about 15 to 20 minutes. The scuba tank was held on the diver's back with a double tank harness, which also held another tank for the diver's breathing air. The air-lift was quite useful for digging small specimens out of sand pockets and grassy areas where other methods of digging were difficult. Alan Emory, of the Institute of Marine Sciences, subsequently used the same apparatus to sample planktonic organisms from the small niches within the coral reef structure. Finding small urchins in the broad, open sand areas presented still another problem. The air-lift was too slow, and digging by hand was un- economical. Surface trawls did not cover enough distance along the bottom (they became clogged within a few meters). A portable 3.5-h.p. water pump was placed in an outboard motorboat, and a 60-meter length of fire- hose with a brass nozzle was used to direct a stream of water at the sand. The jet of water cleared away the sand rapidly, exposing the burrowing animals without harming them. The jet was directed in long, slow sweeps from side to side as the diver moved ahead. By working with the direction of the bottom currents in the area, the silt that was stirred up was carried away from the diver. Tagging, feeding, and behavior experiments were performed in situ, and the methods are described below in the sections on growth, feeding and behavior. Ciliary currents were discerned by using a dissecting microscope and biologically inert fluorescent particles (Tracer-Glow pigments available from Wildlife Supply Co., Saginaw, Michigan) and food-coloring dyes. Small dots of the food dye were placed on the test with a hypodermic syringe; the progress of the ciliary currents was easily traced by the movement of the dye. Movement of sand particles was determined by using black grains of sand. After the animal had begun to burrow into the zone containing the black grains, the burrow was opened up and the progress of these grains was then visible. Movement of particles and feeding methods were observed through a glass-bottomed aquarium. Analyses of the sediment were based on the techniques described by Krumbein & Pettijohn (1938). Core samples were taken by pushing a plastic core tube, 20 cm in length, into the substrate. Both ends of the core tube were then stoppered with rubber plugs. The cores were stored in an ice-cooler and frozen within two hours. H~S was measured with a kit produced by Hatch Chemical Co. Particle size was measured by wet screening through a nest of sieves with mesh sizes of 2.0, 1.0, 0.5, 0.25, 0.125, and 0.062 mm. Silt and clay fractions were separated via liquid suspension (Krumbein & Pettijohn, 1938). Porosity of the substrate was 76 Bulletin of Marine Science [19(1)

FIGURE 2. Adult specimen of Meoma ventricosa (132 mm test length) photo- graphed alive: A, dorsal view; B, ventral view.

determined by measuring the loss in weight of the sand upon drying. Per- meability was measured in a permeameter as described by Stearn (1927). Total organic carbon present was measured by ignition of a preweighed sample to 500°C, at which temperature the organic carbon is driven off as CO2. CaCOx does not burn until a much higher temperature is reached. Crucibles were pre-ignited to 1000°C, cooled in a desiccator, and weighed. Samples were cut from the central portion of a frozen core, using a sterile, stainless steel knife, and then were dried in a vacuum desiccator at 28 Ibsjin2 and 50°C before being weighed prior to ignition.

HABITAT Meoma ventricosa has the greatest ecological diversity of all the West Indian Spatangoida. It has been collected from the intertidal zone to depths of 200 meters, in sediments ranging from fine, heavily silted sand to coral rubble, and in bionomes ranging from beds of Thalassia to coral reef tops and the deeper sea floor. Geographically, this species is known from Santa Marta, Colombia, along the American coastline to Fort Lauderdale, Flor- ida, and from most of the West Indian islands. A few specimens have been taken from Bermuda. Four principal habitats can be delimited for Meoma ventricosa: Thalassia grass with pockets of sand, shallow-water sandy areas with grass and patches of coral, coral reef areas, and deep-water sandy areas. 1969] Chesher: Biology of Meoma ventricosa 77 Thalassia Grass with Pockets of Sand (0-14 Meters Depth).-Specimens of M. ventricosa were found buried or partially buried in patches of calcareous sand within the beds of Thalassia. They tended to congregate to one side of the sand patches, close to the grass. Urchins were found buried between the Thalassia plants where these were not too dense, and occasionally were found covered only with bits of shell and grass in dense grass beds. Where siltation was pronounced (i.e., in Hawk Channel off Key Largo, Florida) M. ventricosa was often found completely uncovered. Under such conditions, abnormal individuals and stunted adults occurred frequently (see section on abnormalities, below). In the pockets of sand, the urchins had a profound effect on the particle- size distribution. The burrowing action of M. ventricosa tended to shift the larger particles to the surface of the substrate and, where the urchins were congregated, the surface of the sand was composed of coarse particles, whereas a few meters away the sand was fine and poorly sorted. Wave action in this habitat is mild; the waves seldom reach more than a meter in height. Tidal currents of up to one-half knot are common. The sandy, grassy habitat where M. ventricosa was found was either part of a reef tract (Florida Keys, Andros, New Providence, the Berry Islands, Abaco, Panama, Grand Bahama) or in protected bay areas (Bimini, Andros, Colombia). Few particles of silica were found in the sand of

these areas, and little or no H2S. Other echinoids found in these areas were Clypeaster rosaceus (found mainly on the grass beds, but also buried in the sand), Clypeaster subdepressus (common only in the deeper areas and covered with a thin layer of sand), Lytechinus variegatus, Tripneustes ventricosus, and Arbacia punctuJata (on the grass beds), Eucidaris tribuloides and Diadema antillarum (usually associated with sponges and small coral heads), and Leodia sexiesperforata (sandy areas).

Shallow-Water Sandy Areas with Grass and Patches of Coral (5-15 Meters Depth).-This area, bordered on one side by Thalassia beds and on the other by shallow-water coral reefs (or deep water) was found to support large populations of M. ventricosa distributed primarily along its borders. Occasionally, a population was found in the center of an extremely large sandy area, but such populations were moving and in time probably congregated along a grass or coral boundary. Along the Florida reef-tract, such sandy areas are often several miles long and average about 400 meters wide. The sand, itself, is clean, white, calcareous, and firmly packed. It usually has deep ripples caused by occasional heavy wave action. The waves reach a maximum of about 1.5 to 2 meters in height. The pattern of ripples is irregularly broken by the traces of the macroinvertebrates liv- 78 Bulletin of Marine Science [J 9(1) ing in the sand. M. ventricosa, Clypeaster subdepressus, Encope michelini, and Plagiobrissus grandis were the most common echinoids in this habitat. The median size of the jagged grains of calcite varied considerably with the local situation but, in the Molasses and Alligator reef areas, averaged about 0.45 mm with a sorting coefficient of 1.54. The total porosity averaged 47.5 per cent, by volume, and the permeability averaged 0.909. H~S was not found in the upper 20 cm of sand. The temperature was normally slightly lower in the sand than in the water during the day. Organic carbon was low, about 1.8 per cent, by weight, of the total substrate (determined by ignition). The dominant microorganisms, other than the bacteria, were the foraminiferans, Archaias depressus and Archaias angularis. The micro- mollusk, Caecum sp., was a dominant form. Diatoms of the genera Cos- cinodiscus and Amphora were common. The sand particles were coated with red, brown, and green algae. Nematodes, microcrustaceans, flagellates and other protozoans were also found as elements of the infauna. The Coral Reef Areas (2 to 20 Meters Depth).-M. ventricosa was often found in the pockets of sand on the coral reefs and in the sandy areas on both sides of the shallow-water reefs. The sand in this habitat was generally coarse, often composed of rounded particles rather than the jagged particles common in the protected sandy areas. M. ventricosa occurred in depths as shallow as two meters in this area. The pockets of sand on the reefs were shared with Paraster floridiensis, Brissus unicolor, Plagiobrissus grandis (young specimens), Clypeaster rosaceus, and Echinoneus cyclostomus. Echinoids of the coral reef also included such non-burrowing forms as Diadema antillarum, Tripneustes ventricosus, Echinometra viridis, and Eucidaris tribu/oides. The reefs are apparently the nursery grounds for M. ventricosa, as it was on the shore- ward side of the reefs that the small M. ventricosa were most abundant. They were buried in the coarse sand beneath and beside large coral slabs, in the same general habitat in which Brissus unicolor is common. Deep-Water Sandy Areas (Over 30 Meters Depth).-M. ventricosa was found in the deeper areas where the reef tract was broken by avenues of sand leading from the shallow-water sandy habitat to the muddy sand areas of the deeper water. In the deep sandy areas, small, widely scattered populations of four or five large adults were found. These populations were not associated with any prominent feature of the bottom. As in the shallow- water populations, the urchins had a pronounced effect on the substrate, creating an area of well-sorted, large particles on the generally fine, sandy bottom. The discrete nature of the disturbed areas indicated that, once established, these small groups remain in one place. These urchins were large adults and always burrowed with the apical spines just at the surface of the sand. 1969] Chesher: Biology of Meoma ventricosa 79

FIGURE 3. Diagrammatic, cross-sectional views of Meoma ventricosa, in situ: A, a young specimen in coarse sand, surrounded by large chunks of coral; B, an adult specimen partly buried in heavily silted sand; C, an adult specimen with only the apical spines showing above the substrate of fine sand; D, an adult specimen completely buried in a substrate of coarse sand. The dark area behind the urchins, which are represented as moving from left to right, indicates the disturbed sand through which .the urchins have just passed.

Of the four environments, the boundary between the sand and coral reef or Thalassia bed supported the largest populations. Heavily silted sand and sand with large amounts of silica were the poorest habitats for M. ventricosa. It is evident that silt and silica sand, which cause an increase in

H2S and decrease in pH and permeability, limit the dispersal of M. ventricosa.

BEHAVIOR Larval individuals of M. ventricosa apparently settle out of the plankton near shallow-water coral reefs or grass beds, since young specimens (8 to 40 mm in test length) were most abundant on the leeward side of such reefs. The young specimens of M. ventricosa were under or near large slabs of coral, beneath 5 to 8 em of sand (Fig. 3,A). The urchins seemed to remain stationary during this early period of growth. The young individuals of M. ventricosa that were about 40 mm in test length were near the edges of the larger sandy patches. Urchins exceeding 50 mm in test length were burrowing in the open sandy areas. A similar distribution occasionally occurred in grassy areas where the young urchins were bur- 80 Bulletin of Marine Science [19(1)

FIGURE 4. Specimens of Meoma ventricosa on the surface of the sand during the night (10 P.M., depth 15 meters, Molasses' Reef).

rowing in the sand between the grass blades or near coral outcroppings, and urchins of greater than 50 or 60 mm in test length were burrowing in the open sandy areas near the grass. Urchins 60 mm in test length were occasionally found emerging from the sand at night. Changes in morphology, growth rates, and pigmentation accompany this increase in mobility. Young M. ventricosa were not commonly found emerging at night until they were about 100 mm long. Depth of Burrowing.-During the daylight hours, the urchins are buried in the sand. The depth to which they are covered depends on size, gonadal condition, rate of movement, the nature of the sand, wave action, and possibly water temperature. As the urchins must move water for respiration through the interstitial spaces of the substrate, they cannot burrow deeper than the length of their apical spines in fine sand or in silty conditions (Fig. 3,B,C). In areas of clean, unsilted sand, these urchins were found as much as 10 cm below the surface of the sand (Fig. 3,D). Wave action, and the subsequent disturbance of the surface of the sand, caused M. ventricosa to burrow deeper into the substrate. M. ventricosa tended to burrow deeper during the colder months of the year, while during the summer months almost all of the urchins were just below the surface of the sand. Urchins which had high respiratory demands (large, ripe, or actively moving urchins) were not buried as deeply as urchins with lower respiratory demands (small, spent, or motionless urchins). The specimens of M. ventricosa which were buried the deepest (their apical spines covered to a depth of 6 to 10 em) were almost motionless during the periods of observation. Emergence at Night.-Shortly after sunset, the adults emerged from the sand (Fig. 4). Not all individuals within a herd emerged to the same extent. Some moved over the sand without disturbing the substrate, while 1969] Chesher: Biology of Meoma ventricosa 81 others remained partly buried and left a distinct trail behind them. Ob- servations made from a towed submarine at night showed that, on any given night, some populations emerged more than others, even in areas of similar depth and sediment type. Urchins at deep-water stations (over 30 meters deep) were not observed emerging from the sand at night. At first, the reason for night emergence seemed to be that the urchins could cover a greater area of sand with less expenditure of energy while feeding on the rich, upper strata. Feeding experiments (see below under food and feeding) showed, however, that the rate of feeding actually slowed at night and, in fact, even stopped when the M. ventricosa moved rapidly along the surface. Of the numerous diurnal changes in the physical environment of the reef areas (Jones, 1963), oxygen saturation may be the most important in causing the emergence of M. ventricosa at night. Jones (1963) showed that a daily fluctuation occurs between 90 and 125 per cent in the saturation of dissolved oxygen in midwater samples taken in the Florida patch- reef environment. At night, when the grass beds and the rich epiflora of the surface of the sand stop producing oxygen and begin producing carbon dioxide, the effect on M. ventricosa must be pronounced. As suggested above, the depth of burrowing of M. ventricosa seems to be controlled by the respiratory demands of the urchins. Therefore, it is probable that, when the interstitial oxygen concentration decreases at night, the urchins move upward and may not attain the necessary degree of oxygenation until completely unburied. Several spatangoids are known to emerge from the sand under conditions of oxygen deprivation in aquaria. Echinocardium cordatum reportedly emerges and moves actively over the sand when water circulation stops in an aquarium (Nichols, 1959). Moira atropos, Brissopsis atlantica, Brissus unicolor, and small specimens of M. ventricosa also emerge from the sand when deprived of oxygen in an aquarium. None of these echinoids are known to emerge from the substrate (except to spawn) under normal conditions. The young individuals of M. ventricosa, which do not emerge at night, have two advantages over the adult urchins: a complete subanal fasciole, and a large ratio between respiratory surface area and volume. When the urchins exceed about 100 mm in test length, their respiratory surface area and burrowing capability apparently cannot maintain internal homeostasis except in highly oxygenated conditions. Plagiobrissus grandis, another spatangoid that inhabits the same substrate as M. ventricosa and grows to an equally large size, does not normally emerge from the sand at night. Plagiobrissus grandis differs from M. ventricosa primarily in being better equipped to maintain its respiratory needs through a more efficient circulation system within its burrow. It seems likely, therefore, that the emergence of M. ventricosa at night is linked to 82 Bulletin of Marine Science [19(1) respiration. Such an explanation also agrees with the observed variation in the degree to which individuals and populations emerge. Respiratory demands would fluctuate greatly between individuals and between populations, and variability in bottom currents with different oxygen concentrations could explain the differences in emergence exhibited by neighboring herds. Rates of Movement.-Individuals of M. ventricosa moved at about 3 to 6 em per hour during daylight hours. Movement varied greatly from day to day and between individuals. Urchins were frequently motionless when they were buried deep in the sand or when they had met an obstacle such as a rock or grass roots. Although urchins were found moving at about 115 em per hour at night, the average rate of movement at night was only 7 or 8 em per hour. Movements at night were erratic, and periods of motionlessness were followed by rapid movement for a meter or so. Direction of Movement.-A series of experiments was conducted at Alli- gator Reef to determine the movements of individual urchins over a five- day period. Five groups of 10 urchins were marked and placed on the bottom. Each group was arranged in a small circle, with the anterior ends of the echinoids facing outward from the center in order to reduce any initial bias in directionality. Movement over the five-day period was ran- dom and erratic. No orientation was found for individuals or for the group as a whole. Tagging experiments over a period of one year showed that there was only a slight movement of individuals out of enclosed sand patches. Structure of Population.-The tendency of M. ventricosa to form discrete groups or herds was most evident when surveying large sandy areas at night. Large expanses of sand had no urchins at all. When a herd was found, densities of 2 or 3 specimens of M. ventricosa per square meter were common. The periphery of the herd was usually clearly defined, and the general outline of the herds tended to be oval. These herds, if not enclosed by grass or coral boundaries, could move as a unit slowly over the sand. This was evident from broken and bare tests which were found near the populations, presumably having been left behind as the herd moved on. One herd moved past a coral outcropping near Molasses Reef at a rate of approximately 50 meters in six weeks. Another, smaller herd moved down a slope from Molasses Reef to the 30-meter level, a distance of about 150 meters, in less than one week. Apparently, these urchins had a strong orientation down the slope. In Santa Marta, Colombia, a small group of 5 urchins was found on a 10° slope. It was evident from the area of disturbed sand and the trails in the sand that these urchins were not oriented down the slope as was the Florida herd. Herds moved slowest, if at all, 1969] Chesher: Biology of Meoma ventricosa 83 in deep water and where they had become trapped in a pocket of sand bordered by grass or coral. Samples of the substrate within and outside the boundaries of the herds located on the open sandy areas showed no major differences other than an increased permeability, which was probably due to the activities of the urchins. It was concluded that the major factor causing the urchins to form herds is a function of the urchins, themselves. Bader (1952) presents evidence for a similar conclusion for herds of the sand dollar, Echinarach- nius parma. Unless the individuals of M. ventricosa were reacting to the increased permeability of the sand due to their own burrowing action, the most reasonable explanation for the formation of herds is that the urchins were responding to dissolved organic products resulting from their normal metabolic activities. FOOD AND FEEDING Each adult Meoma ventricosa ingests the sandy substrate with 56 spe- cialized feeding tube-feet which surround the mouth (Fig. 5,B). These tube-feet are extended with the disc flattened and the digits protruding. The surface of the disc is coated with a sticky mucus secreted by mucous glands in its epithelium, and the digits are supported with calcitic spicules. When the disc contacts the substrate, the foot is retracted with the disc folded shut and with sand caught between the digits. The tube-foot is then thrust into the mouth where the disc everts, depositing the sand in the oesophagus. There is no indication of selective feeding on particles. Particles are ingested which just barely fit through the peristome. Occasionally, the oral spines assist the tube-feet in moving large particles into the mouth. The animal does not use its labrum as a "shovel." The gut is firmly packed with sand (Fig. 11). Only the upper part of the intestine and the rectum are partially empty. The digestive process was not studied, but it is evident that Eichelbaum's (1910) analysis of spatangoid digestion is improbable. His theory requires the sand to remain in the gut a long time. The larger particles are supposedly broken up until they can fit through the small anus in the center of the periproctal system. Feeding experiments in the field show that M. ventricosa can move the sand completely through the gut in four hours and that the periproctal system is quite flexible. Both the anus and the mouth can dilate to the full extent of the opening in the test, and both close rapidly when the animal is disturbed. All preserved specimens have the periproct and peristome closed unless the animal has been anesthetized before preservation. Rate of Feeding.-Feeding experiments were conducted during both the day and night. To determine the rate at which sand was ingested, a pipette filled with a suspension of inert fluorescent powder in sea water was introduced into the burrow directly in front of the mouth of M. ventricosa. This 84 Bulletin of Marine Science [19(1)

FIGURE 5. A, commensal crab hidden in peristome of M. ventricosa; B, the peristome of M. ventricosa showing the feeding tube-feet. 1969] Chesher: Biology of Meoma ventricosa 85 was accomplished by sliding the pipette through the sand to a point just anterior to the notch in the anterior portion of the test. The opening of the pipette was pushed below the level of the urchin and the pigment steadily released as the pipette was withdrawn. The initial position of the urchin was marked with a small stake. Twenty-five urchins were fed the pigment, and 15 urchins were used as control specimens. At the end of each hour the movement of five urchins was measured, and they were collected. The oral portion of the urchin was removed, and the position of the fluorescent "ring" was noted in its progress along the gut. After all five echinoids had been opened and inspected, they were taken to the boat, where the gut was severed at the point of concentration of the fluorescent pigment. The severed anterior and posterior portions of each gut were placed in labeled containers. Later the sand was removed from each portion of the gut, and the volumes of these two samples of sand were determined. The two samples were then dried and weighed, and the amount of sand ingested by that animal during the experimental period was expressed as a percentage of the total amount of sand in the gut. By the end of the fourth hour, the fluorescent pigment had entered the second loop of the gut, and could not be followed because of mixing of the sand. At night, the same procedure was followed, with the exception that it was easier to place the pigment directly in front of the feeding tube-feet. The results of a typical experiment are shown in Table 1. Since feeding experiments were not performed on small specimens, the feeding rates obtained are only representative of adults. The average length of time for the sediment to pass through the gut was 4.5 hours, and the average rate of ingestion was 25 ml of sand per hour. Feeding was not directly related to the rate of movement and was greatest during the daylight hours when the animals were burrowing through the sand at about 6 cm per hour. At night, those echinoids moving at more than 65 cm per hour were found to be feeding very slowly or not at all. Others, moving at a more normal speed of 7 cm per hour were found to be feeding at an average rate such that the sand would pass through the gut in 7.3 hours.

EFFECT OF M. ventricosa ON THE SUBSTRATE Densities of three specimens of M. ventricosa per square meter are not uncommon within herds. In enclosed grass patches, the number may go as high as four per square meter. In one area (Molasses Reef Sta. 1) completely enclosed by grass, there were three specimens of M. ventricosa per square meter, and the average width of test was 110 mm. Since the urchins disturb the sediment directly above the ambitus as well as that which the test must pass through, one can assume the amount of sand moved is equal to the width of the urchin times the depth to which the lower portion of the animal is buried times the rate of movement. The 86 Bulletin of Marine Science [19(1) TABLE 1 FEEDING RATES AND MOVEMENTS OF Meoma (7/16/66, 1100 to 1600 hrs, 6 meters depth, Molasses Reef, Station RHCK 60)

Test Depth Dist. Sand Time to pass Time length covered' moved ingested Sand Per cent through gut" (hrs) (em) (em) (em) (ee) left" ingested (hrs) 1 12.5 0 5 26 98 21 4.8 1 11.0 2 3.5 20 63 24 4.2 1 10.5 1 6 24 85 22 4.5 1 11.3 0 9 28 112 20 5.0 1 10.2 0.5 6 20 57 26 3.8 2 9.8 0 10.5 38 34 53 3.8 2 12.8 0 12.5 50 70 42 4.8 2 13.0 0 10 56 65 46 4.4 2 13.1 1 14 68 80 46 4.4 2 11.5 0 12 52 66 44 4.5 3 12.8 1 15 78 444 64 4.7 3 10.6 0 19 62 334 65 4.6 3 11.2 0.5 21 69 48 59 5.1 3 13.2 2 19 81 544 60 5.0 3 12.2 4 14 77 364 68 4.4 4 10.0 0 24 traces of pigment in 2nd loop 4 13.0 0 28 traces of pigment in 2nd loop 4 12.9 0 19 traces of pigment in 2nd loop 4 13.1 I 22 traces of pigment in 2nd loop 4 11.9 0 12.5 traces of pigment in rectum 5 10.7 0 34 traces of pigment in rectum 5 11.1 1 20 pigment not found 5 13.0 0 28 pigment not found 5 12.9 0 32 pigment not found 5 12.0 8 0 15 106 125

1 Depth of sand coveringthe tips of the apicalspines. ""Sand left" refers to the as yet unexcretedportion of that sand that was in the gut prior to the beginningof the experiment. S Extrapolatedtimenecessaryfor sandto passthroughthe gut. • Exact locationof pigment-ladensand questionabledue to mixingin secondloop of intestine. • Deeplyburied specimenwas not feedingnormally. Averagerate of movement= 5.8 cm/hr. Averagerate of ingestion= 25 cc/hr. Averageperiodto pass sand throughgut = 4.5 hr. average depth of the lower part of the animals at Sta. 1 was 6 em, and the daytime rate of movement was 5 em/hr. The amount of sand turned over by each echinoid was, therefore, 11 x 6 x 5, or 330 cc per hour. One cubic meter of sand 6 em deep contains 6 x 104 cc of sand. At a density of three specimens of M. ventricosa per square meter, 990 cc of sand are overturned each hour within one meter. Thus, it requires only 60.6 hours for the M. ventricosa to disturb their entire habitat within that particular patch of sand. 1969] Chesher: Biology of Meoma ventricosa 87 The average rate of feeding was 25 cc per hour per urchin. Therefore, it would require 800 hours before all of the sand would be passed through their intestines. Since the continual overturn of the substrate helps to increase the water content and provide fresh surfaces for algal and bacterial growth, the activities of the urchins probably stimulate microbenthic ac- tivity and so help to maintain the amount of food available. Since M. ventricosa is the largest and most abundant macroorganism in the sand of many areas, its influence on the distribution of sedimentary particles and on the productivity of the sandy areas must be pronounced. Each M. ventricosa disturbs about 48 square meters of substrate to a depth of 6 cm each year. Assuming that the individuals of M. ventricosa do not cover the same areas again and again (as they do in enclosed pockets of sand), an area with a density of more than one M. ventricosa per 48 square meters would be completely disturbed in one year.

GROWTH Growth Rates.-Tagging experiments were carried out on a population of M. ventricosa from the sand-Thalassia habitat near Molasses Reef in the Florida Keys. The urchins were located in a single patch of sand bordered on all sides by a scant growth of the marine angiosperms Thalassia and Diplanthera. Tagging and recovery were performed under water to minimize any possible effects that handling the urchins might have on growth rates. Each urchin was removed from the sand and placed on a transparent, plastic marking board (Fig. 1). The animal was positioned with the most anterior portion of the test against the rigid plastic upright and the movable arm of the measurer was pushed firmly against the posterior portion of the test. A beveled edge on each of the opposing uprights moved the spines aside so that measurements were made on the test itself. A line was drawn on the measuring board and a number written next to it. The same number was written on the urchin between the peripetalous fasciole and the ambitus in interambulacrum 1. An ordinary No. 3 lead pencil was used for both operations. While numbering the urchin, a firm pressure on the pencil removed the spines and ground the graphite into the surface of the test. The urchin was then returned to the substrate and covered with sand. About 50 urchins could be marked in one hour. When the urchins were recovered, the mark was usually renewed as the spines and epithelium regenerated within one month. Urchins left for over one year still showed some traces of the number underwater but these had to be killed and the spines and tissue cleaned off with bleach before the number could be read clearly. The rapid regeneration of the tagged area and the similarity of growth rates between urchins tagged once and those retagged several times in- 88 Bulletin of Marine Science [19(1) 14

-""co '=:8 ...-•..~ 6

o o 2 3 4 Years FIGURE 6. The growth curve of M. ventricosa derived from tagging experiments. dicated that this method of tagging did not alter the growth rate of the urchins significantly. During March and April of 1965, 150 specimens of M. ventricosa were tagged. Forty-eight additional small urchins were tagged as they were found and were added to the population. Of the 198 specimens of M. ventricosa tagged, 117 urchins were recaptured (some of those recaptured were removed from the population while others were retagged and left in the population). Of the 117 individuals examined for a period of two months or longer, 48.6 per cent showed some growth and 51.4 per cent showed no growth. Growth was followed for 37 individuals for one year or more, and, of these, only 37.9 per cent showed no growth. Urchins which had apparently stopped growing ranged in size from 109 to 144 mm test length. Since an estimate of the maximum growth rate of M. ventricosa was sought, urchins which had already stopped growing were not included in the calculation of the growth curve. The growth curve (Fig. 6) was cal- culated from a Walford Line (Ricker, 1958) using the 57 specimens which showed some growth during a two-month (or greater) period. If the in- terval of time was greater than two months, the growth vs. time was plotted and interpolated to the standard two-month period. The least- square line for the Walford plot (Fig. 7) is L = 0.84Lt + 21.82. Loo,the maximum size to which M. ventricosa is likely to grow, is 136.4 mm. Thus, 1969] Chesher: Biology of Meoma ventricosa 89

13 ~on =12 0 E N ,:!:.11 -..• :;10 ••••...c -'9

7 8 9 10 11 12 13 14 15 Test Length (em) at T

FIGURE 7. Walford plot showing the length at tagging (T) versus the length at recapture 2 months later (T + 2 months).

M. ventricosa grows to about 88 mm in 12 months, 120 mm in 24 months, 130 mm in 36 months, and 134 mm in 48 months. This rate of growth refers to populations of M. ventricosa living in sandy patches within Thalassia beds. Individuals of M. ventricosa from siltier habitats do not grow as large, and those urchins from open sandy areas and from greater depths grow to a larger size. In an inshore, silty area near Key Largo, Florida, the mean length of test for 52 individuals was 112.4 mm, and the maximum length of test found over a two-year period was 124 mm. In an offshore area of coarse sand near Molasses Reef, a herd of about 112 individuals showed a mean length of 139.1 mm, and the maximum size found over a two-year period was 169 mm. Since the tagging experiments showed little or no interchange of urchins from one population to another, it can be assumed that the 124-mm and the 169-mm maxima are representative of the L" of the two areas. The Effect of the Environment on Growth.-It is of interest that the available food does not seem to be the major parameter controlling growth rates in M. ventricosa. The organic content of the two areas (determined 90 Bulletin of Marine Science [19(1)

, 9>>1 .4 ,, ...•0•.... ,, .3 0-_ ••__ ""'0.. 1965 -66 .2

o MAR APR MAY JUN JUL AUG 100

o 1964 1965 FIGURE 8. Changes in gonadal indices for female specimens of M. ventricosa during 1964 to 1966, and the changes in gonadal condition from 1964 to 1965. by ignition) was 2.2 per cent, by weight, of the sand in the silty habitat and 1.8 per cent, by weight, of the sand in the open sandy areas. Popula- tion densities in the open sandy areas were as great as, or greater than, in the silty areas. The total available organic material per urchin was, therefore, found to be higher in the inshore station where the urchins were growing more slowly, and to a smaller size, than the urchins from the offshore, open sandy areas. Bader (1952) found a peak concentration of the sand dollar, Echinarachnius parma, in areas with an organic content of 0.917 to 0.977 per cent of the total substrate. The numbers of echinoids decreased as the organic content increased. The inshore urchins spend more time on the surface of the sand than do the offshore urchins, probably because of the increased silt content of the substrate and the pronounced changes in oxygen concentration associated with the grass beds. Some populations in deeper areas, particularly those in depths greater than 30 meters, were found completely buried at 1969] Chesher: Biology of Meoma ventricosa 91 night. Apparently, these were not subjected to the same environmental pressures as populations in shallower areas, and, although the feeding rates of these deeper water populations were not measured, it is believed they were feeding normally while buried. If this is true, one explanation for the size differential could be that the large urchins from the deep-water stations feed continuously, whereas those in shallower water spend considerable time feeding slowly, if at all, on the surface of the sand. The low concentration of oxygen found at night in the areas containing Thalassia may, in addition to slowing the growth by decreasing the amount of time spent feeding, act directly upon the growth rates. If the urchins are sufficiently affected by the low concentration of oxygen to stop their feeding, it is likely that other physiological activities might be slowed or stopped during the period of stress.

REPRODUCTION Gonadal Volume.-Changes in gonadal volume were followed from Sep- tember, 1964, to August, 1966. The gonadal indices (10 X gonad volume/ test volume) for female individuals of M. ventricosa are plotted in Figure 8. Male gonadal development closely paralleled the female development and averaged about 8 per cent less in volume than female gonads. The degree of ripeness was determined by gonadal smears. Some ripe males (indicated by viable sperm in the gonadal smear) were available all year. Development of female gonads was recorded as spent (no ova), small ova (developing, nucleate ova less than 0.19 mm in diameter), large ova (0.19 to 0.29 mm in diameter but still nucleate), and some ripe ova. Only one individual was found with more than a few ripe ova. Spawning.-In March of both years, individuals of M. ventricosa were completely spent, and had a gonadal index of 0.18. Gonads developed rapidly, reaching a peak index of 0.55 in July of 1965, and a peak of 0.46 in August of 1966. Some urchins with ripe ova were present in August, as were a few spent individuals. Spawning began, therefore, sometime in August and continued until February. The peak spawning period was from November to January. Almost all males were ripe from June to February. On January 3, 1964, at 4 P.M., spontaneous spawning of a male M. ventricosa was observed. The urchin was buried to the peripetalous fasciole. No external stimulus was noted. The animal spurted a milky column of sperm about 20 em into the water. This was repeated twice at intervals of about two minutes. The sperm dispersed and drifted away with the slow bottom current. Other urchins nearby (including those down-current from the spawning individual) were not spawning and showed no reaction. The male remained motionless for one hour, at which time observation was discontinued. 92 Bulletin of Marine Science [19(1) Moore & Lopez (1966) indicated that the lack of fully ripe females in Moira atropos may be an indication of repeated, limited spawning periods which are possibly correlated with lunar phases. Thus, a proportion of the ova ripen and are released monthly. If this were so, the ripe ova should be concentrated near the oviducts and the unripe ova confined to the areas adjacent to the gonadal walls. Sections of female gonads with some ripe ova show that the ripe ova are randomly distributed among the nucleate ova. The ripe ova can be found in any portion of the gonad, and it is doubtful that these could be sorted out just prior to a monthly spawning. When spent females are found, they are thoroughly emptied of ova (with the exception of a few large ova which are in the process of breaking down). On August 28, 1963, a specimen of Moira atropos was found which contained about 85 per cent ripe ova 0.12 mm in diameter. When the ovaries were removed, the ripe ova were ejected from the torn oviduct in a steady stream. The ova were fertilized and larvae developed to the five-armed pluteus stage. On November 21, 1964, one M. ventricosa was found with about 80 per cent ripe ova. As with the specimen of Moira atropos, the ova were ejected in a steady stream from the oviduct. This would indicate that when Meoma ventricosa or Moira atropos spawn, they release the genital contents completely and not in small portions. Since fully ripe individuals have not been found and since the gonadal volume of the entire population decreases at a steady rate during the spawning period (Fig. 8), it is evident that spawning must occur on an individual basis and not as a single mass spawning. The evidence further suggests that the ova are kept in an immature state and, when the proper stimulus occurs, ripen in a few hours (or minutes) before being shed. Chaet (1966) has shown that the nucleate ova of asteroids can ripen in a few minutes after the addition of an extract from the radial nerves. Spawn- ing may well occur at night, explaining the lack of ripe females in the samples which have been taken during the day. Holland (1967), for the cidarid Stylocidaris affinis, noted a phenomenon similar to that now found for M. ventricosa, and suggested a rapid maturation of ova just prior to spawning. Holland's contention that this type of gametogenesis is evidence supporting separation of the cidarids into a sub- class Perischoechinoidea is poorly based. Meoma ventricosa and Moira atropos have a gametogenic process that is very similar to that of Stylo- cidaris affinis, whereas gametogenesis in Echinocardium corda tum is similar to that of other "Euechinoidea" (Moore, 1936). Maturation.-Although genital pores appear in M. ventricosa at a test length of between 39 and 52 mm, gonads do not mature until the test length is about 90 mm. As in Moira atropos (Moore & Lopez, 1966), larger first- year individuals of M. ventricosa may spawn to a limited degree, but major 1969] Chesher: Biology of Meoma ventricosa 93 spawning probably begins during the second year of life. Larger specimens of M. ventricosa produce more gonadal material relative to the test volume than do smaller individuals. Thus, the mean maximum gonadal index for those specimens of M. ventricosa that were 120 to 125 mm long was 0.49 in 1965, while those that were 135 to 140 mm long had a maximum gonadal index of 0.68 during the same period. One specimen, 165 mm in test length, had a gonadal index of 0.77. Comparison of Gonadal Production to That of other Spatangoids.-AI- though there is a considerable difference in adult size between Meoma ventricosa (130-140 mm test length) and Moira atropos (40-50 mm test length), their relative gonadal production is similar. The maximum gonadal index for Moira atropos was found to be 0.62 in 1964, and 0.47 in 1965 (Moore & Lopez, 1966). The maximum gonadal index for Meoma ventricosa was 0.55 in 1965, and 0.46 in 1966. Echinocardium cordatum in England reaches a gonadal index of 1.1 (Moore, 1936). Moore & Lopez ( 1966) attributed the larger gonadal index of the northern urchin to the fact that it has four gonads, whereas Moira atropos has two. Meoma ventricosa, however, also has four gonads. It is interesting that the two tropical spatangoids, despite differences in size, habits, and habitat, have similar gonadal indices, although the similarity may be coincidental.

PREDATORS The adult Meoma ventricosa has few predators. Its large size, sturdy test, burrowing habit, and chemical makeup are effective protection against many echinoid predators. Animals which were observed feeding on Meoma ventricosa include a loggerhead turtle (Caretta caretta caretta), a large stingray (Dasyatus americana), helmet shells (Cassis madagascariensis), a crab (Calappa flammea), a hogfish (Lachnolaimus maximus), and a parrot fish (Sparisoma aurofrenatum). The turtle, which was observed in a broad sandy area off Lower Mate- cumbe Key, Florida, bit a large M. ventricosa, crushing the test into several large pieces, and then swam off, leaving the broken test scattered on the bottom. Only a few fragments of the test and portions of the intestine and gonads were missing from the remains, indicating that the turtle was either frightened off by my proximity or did not find the urchin acceptable food. The stingray, observed on the sand near a turtle-grass bed, was first seen lying motionless on the surface of the sand. When prodded, it swam off, disclosing the remains of a partially eaten adult M. ventricosa. About half the test was broken away, and a portion of the internal organs was missing from the urchin. The crab was observed eating a specimen about 85 mm long. One claw 94 Bulletin of M'arine Science [19(1) was used to hold the urchin against the anterior portion of the crab while the other claw was used, much like a can opener, to break away the dorsal portion of the test. Only the gonads and a portion of the intestine were eaten by the crab during about one hour of feeding. Numerous specimens which had been similarly "opened" were found during the course of this· study, and it is thought that this crab may be the major predator of small individuals of M. ventricosa in some areas. The helmet shell, Cassis, feeds by drilling a hole through the test and digesting all of the urchin, leaving only a bare test behind (Moore, 1956). Cassis madagascariensis, which normally feeds on Plagiobrissus grandis,. was found eating a M. ventricosa (112 mm test length). Several other tests which had been drilled by Cassis were found during the study, but the much greater incidence of drilled tests of Plagiobrissus grandis indicated that M. ventricosa is not the preferred food of Cassis. Some of the drilled specimens of M. ventricosa had been partially eaten, and some had not been eaten at all. The conclusion is that Meoma ventricosa is not commonly preyed upon by Cassis. The hagfish, Lachnolaimus maximus, was seen biting an adult M. ventricosa. Teeth marks could be clearly seen in the injured specimen but the test was not broken. Kier (Kier & Grant, 1965) observed a small parrot fish (Sparisoma aurofrenatum) feeding on the spines of M. ventricosa. Kier also observed a starfish (Oreaster reticulatus) eating M. ventricosa. This starfish is a general omnivore which eats any available injured or decaying material. The injuries described by Kier & Grant (1965) as occurring on many specimens of M. ventricosa can be caused by an infection which occurs when, for prolonged periods of time, the animals are unable to burrow. Such injuries also developed in a number of specimens kept in aquaria. The spines of the infected area dissolved or fell off, and the integument turned purple-brown; often a depression was dissolved in the test and the limits of infection were clearly shown by an abrupt change from healthy to infected tissue. Boolootian et al. (1959) reported a similar "peculiar disorder" in specimens of the regular echinoid Allocentrotus fragilis kept in aquaria. While the starfish could have been preying on a healthy M. ventricosa, it may have been feeding upon an infected animal. In any case, no other instances of starfish feeding on M. ventricosa were found. Even the other animals listed above do not seem to be active predators of M. ventricosa, and none are known to depend on it as a source of food. In contrast to what occurs for other echinoids, when the test of M. ventricosa is broken and scattered about underwater, fish do not rush in to eat the remains. When disturbed, M. ventricosa secreted large amounts of a yellowish pigment which was repellent to small fish and killed both small fish and 1969] Chesher: Biology of Meoma ventricosa 95 crustaceans in confined conditions. The pigment is water soluble and tastes strongly of iodine. The degree of pigmentation increases with age. No other spatangoid is known to produce such a large amount of pigment and it is probable that the rapid secretion of pigment when the animal is phys- ically injured or disturbed acts as a deterrent to predators.

PARASITES AND COMMENSALS A small pinnotherid crab, Dissodactylus sp. (Fig. 5,A), occurred on almost all large specimens of M. ventricosa examined. It was not found on specimens smaller than 60 mm in test length. It was not found on other species of urchins, including Plagiobrissus grandis, in the same localities, and may be considered specific for M. ventricosa. If dislodged from the host, the crab hid among the spines of any burrowing echinoid in the vicinity. The crabs were most commonly found on the oral surface of the urchins and often, when the urchin was picked up, the crab moved toward the peristome. On one occasion, a crab moved into the mouth of the urchin and was subsequently found unharmed in the oesophagus. Although one or two crabs per urchin seemed to be the average number per host, some urchins carried as many as 12 crabs of various sizes. The relation- ship of this crab to M. ventricosa was not studied in detail, but there was no evidence to indicate that the crab injured the urchins. An undescribed gregarine protozoan of the genus Lithocystes frequently occurred in the coelom of M. ventricosa. Unidentified flagellates occurred in the gonads of several specimens. Initially, they were noticed in a specimen with large ova and were thought to be sperm until viewed with a phase-contrast microscope. The flagellates are triangular, and each angle bears a long flagellum.

ABNORMALITIES Three types of abnormalities were found in M. ventricosa. The abnormalities resulted from: (1) growth changes due to environmental conditions, (2) regeneration of injured areas of the test, (3) genetic abnormalities. Figure 9,A shows the posterior portion of a M. ventricosa which has apparently regenerated a broken area of its test. Figure 9,B shows a similar regenerated area on the dorsal side of the test of another specimen. De- formities of this type were characterized by sharp, jagged edges which remained where the plates were broken or penetrated. One specimen was found with broken plates joined to the test by thick, partially calcified tissue. Two specimens were found which had apparently been drilled by Cassis and then released. In one of these specimens, the hole was closed over with a thin membrane, while in the other the missing portion of the test had been completely regenerated, leaving a small, sunken, circular cavity 8 mm in diameter, covered with spines and pedicellariae. 96 Bulletin of Marine Science [19(1)

FIGURE 9. Abnormal specimens of M. ventricosa: A, regenerated area of the posterior portion of the test; B, regenerated area on the dorsal portion of the test; C, D, specimens with concave dorsal surfaces; E, abnormal development of the peripetalous fasciole on the posterior portion of a specimen; F, ambulacrum III of a specimen of M. ventricosa with functional respiratory tube-feet here as in the other petaloid areas. 1969] Chesher: Biology of Meoma ventricosa 97 Figure 9,C,D shows two specimens with concave dorsal surfaces. Urchins with varying degrees of this deformity were not uncommon in areas of silt and grass. Forty-three per cent of one population (Hawk Channel, off Key Largo, Florida) were afllicted. The extreme variability in the degree of deformation and the localization of deformed individuals in areas of environmental stress indicated that the deformities were environmentally, rather than genetically produced. Such monstrosities would result if growth in the apical region were retarded while the ambital plates grew normally. Inhabitants of habitat 1 (discussed above under habitats), because of Thalassia or a thin cover of sand, do not burrow normally and are often constantly exposed. The concave dorsal surface, therefore, may be related to the inability of the urchins to cover their apical areas with sand. The work of Pequignat (1966) indicates that echinoids may digest organic material externally and absorb it directly through the integument. This hy- pothesis is quite reasonable when applied to burrowing urchins. The in- numerable spines provide an enormous surface area for absorption, and the controlled current action through the burrow provides an excellent opportunity to utilize dissolved organic substances or particulate matter. Fer- guson's (1967) autoradiographic analysis of absorption of amino acids through the epidermis of asteroids shows that nutrients absorbed through the integument do not enter the coelom, and it may be assumed that the effects of uptake are local and proportional to the nutrients and water movements adjacent to the epidermis. Thus, when the urchins are pre- vented from burrowing, the apical area would derive less nourishment than the ambital area and the resulting change in growth gradients could produce a depressed dorsal surface. Genetic abnormalities, or those deformities which have no apparent relation to the environment and occur in similar proportions in all populations, were common in the specimens of M. ventricosa from Florida. The most frequent deformities were abnormal peripetalous fascioles. Accessory branches, deviations from the normal location, or splits in the fasciole were common. Figure 9,£ shows a specimen with all of these deformities. M. ventricosa is an unusual spatangoid in that the portion of the subanal fasciole nearest the anus vanishes with growth. This condition is shared with the Pacific species, M. grandis, but not with the African species, M. cadenati. Two specimens of M. ventricosa (135 mm and 157 mm in test length) found at Bimini, Bahamas, and Santa Marta, Colombia, retained the entire subanal fasciole. The dorsal sections of the fascioles were not, however, as broad as those found in the African species. Respiratory tube-feet in an otherwise normal frontal ambulacrum were found on one specimen (Fig. 9,F). The frontal ambulacrum normally contains small, single pores which bear sensory tube-feet lacking a terminal disc. In the entire suborder Amphisternata, which includes M. ventricosa, 98 Bulletin of Marine Science [19(1) 1969] Chesher: Biology of Meoma ventricosa 99 respiratory tube-feet are unknown in the frontal ambulacrum. Two fossil genera, Plesiaster (upper Cretaceous of Europe, N. Africa, and N. America) and Brissolampas (Miocene of Italy), have pore-pairs in ambulacrum III indicative of respiratory tube-feet. The anomalous Meoma ventricosa is thus an extraordinary monstrosity.

PEDICELLARIAE Tridentate (Fig. 1O,C), rostrate (Fig. 1O,A,B), ophicephalous, and triphyllous pedicellariae are common on the adult urchins and resemble those described by Mortensen (1951). As suspected by Mortensen, globi- ferous pedicellariae (Fig. 10,D,E) are present on young specimens. They were found on specimens 38, 32, and 8.5 mm in test length, but were generally rare. As in M. grandis, the valves are small (0.2 mm long) and black. The stalk (Fig. IO,E) is short (0.23 mm) and has a pronounced limb near its base. The terminal openings of the valves are surrounded by 7 to 12 small teeth and vary in shape and relative size. A specimen from Bermuda (MCZ 8190, 153 mm in test length) has numerous large globi- ferous pedicellariae in the ambulacral areas adjacent to the plastron and epiplastron. The valves are 1 mm long and the stalks, which measure 1.3 mm, have a pronounced limb near the base. The valves and stalks of the Bermudan specimen closely resemble those of the young specimens from Florida.

INTERNAL ANATOMY AND FUNCTION Figure 11 represents the internal anatomy of M. ventricosa. Sand is introduced via the feeding tube-feet into the oesophagus (0). The intestine is so extremely thin walled that sand grains and particulate matter can be seen through it. Slow peristalsis moves the tightly packed sand through the oesophagus and intestine. Water is removed from the sand at the junction of the primary siphon and the gut (j). The primary siphon shows pronounced and rapid peristalsis and small particles of pigment can be seen moving along its length. The water is returned to the gut just before the second intestinal loop, possibly to aid the transport of sand past this 1800 bend by increasing the liquid content. The gut, between the origin of the primary siphon (j) and the junction of the secondary siphon (S2), is highly vascularized. At the end of this vascularized area, the secondary siphon removes additional water from the sand, returning it again a short distance farther along the intestine. Just opposite the origin of the secondary siphon, the caecum (c) attaches to the anterodorsal portion of the intestine. The caecum is a highly vascularized, thin, convoluted sac which occupies a major portion of the coelom between the intestine and the gonads. Sand does not enter the caecum. Sand progresses through the lower intestine to the upper intestine, and is 100 Bulletin of Marine Science [19(1) 1969] Chesher: Biology of Meoma ventricosa 101 finally pushed through the rectum to the anus, which dilates periodically to release the sand. The haemal system is similar to that described by Koehler (1883) for Brissus unicolor. An inner vessel (v) adjoins the primary siphon. It divides in the vicinity of the oesophagus, and one branch connects to the caecum while the other connects to the haemal ring encircling the peristome. The outer vessel (ov) originates at the peristome in interambulacrum 4. It attaches to the mesenteric system of the oesophagus and lower intestine. The heavy, sand-filled gut is supported by mesenteries located along the entire course of the intestine. The inner portions of the intestinal loops are attached to one another by mesenteries, dividing the coelom into upper and lower sinuses. The coelomic fluid is circulated by ciliary action of the peritoneum (Fig. 13,D). A strong current was detected moving anteriorly along the oesophagus. This current originates from fluids flowing centrally from the median, ventral portion of the first loop of the intestine. With the exception of this current, which seems to be a localized circulation in the vicinity of the mouth, the currents radiate outward over the intestine and mesenteries to the wall of the test. In general, the currents flow in an opposing direction along the adjacent parts of the wall. Currents are most pronounced on the oesophagus, the highly vascularized portion of the intestine, the caecum, the ampullae of the tube-feet, and the gonads.

RESPIRA TORY CURRENTS The respiratory currents of the petaloid area are shown in Figure 12. The solid arrows indicate the direction of flow of currents on the external and internal portions of the test, as determined from observing the flow of small concentrations of food dye and small particles of fluorescent plastic. The dotted arrows indicate the flow of currents within the tube-feet and ampullae as determined by the observation of the movements of small pigmented particles which occur naturally within the water-vascular system. A counter-current system was found similar to that recorded from the respiratory organs of many aquatic animals including oysters and fish (Prosser & Brown, 1962). The effect of this system is to increase the efficiency of oxygen exchange through the respiratory membranes. The respiratory tube-feet (g) and the ampullae (a) are subdivided internally into numerous small sinuses and the surface of the tissue is convoluted, particularly on the ampullae. The currents flowing through and around this system are vigorous. Current flow through the feeding tube-feet is somewhat different. There is only one pore through the test, and the currents flow into the bulb- shaped ampulla from the tube-foot along the walls of the pore and ampulla, and leave through the center of the ampulla and pore. 102 Bulletin of Marine Science [19(1)

FIGURE 12. Diagrammatic view of a portion of the respiratory petal of M. ventricosa showing the two rows of gill-like tube-feet (g) and the convoluted ampullae (a). The solid arrows represent water currents on the outer portion of the test and coelomic-fluid currents on the inner portion of the test. The dotted arrows indicate the flow of the fluids within the water-vascular system.

MOVEMENTS OF WATER AND PARTICLES IN THE BURROW

Figure 13,A-C shows the movement of sand and water within the burrow of M. ventricosa. The dotted lines represent movement of sand and the solid lines represent movement of water. Circles with a dot in the center represent areas where the current leaves the surface of the test. Since the burrow of M. ventricosa does not communicate with the surface of the sand, the circulation of water for respiration is a problem. Water is obtained by drawing the surface water through the interstices of the sand (or, in silty areas, through the opening kept open by the apical spines). The water flows outward from the apical system, as shown in Figure 13,A, past the respiratory tube-feet, and through the peripetalous fasciole. The water must then be forced out into the interstices of the surrounding sand. Since the permeability of the substrate normally decreases 1969] Chesher: Biology of Meoma ventricosa 103

FIGURE 13. A-C, movements of water (solid arrows) and particles (dotted arrows) within the burrow of M. ventricosa. Circles with a dot in the center indicate areas where the water currents leave the burrow. D, the flow of coelomic fluids within the test of M. ventricosa, as viewed from the ventral side. 104 Bulletin of Marine Science [19(1)

PPF FIGURE 14. The function of the peripetalous fasciole. The diagram shows the fasciole (PPF) with the respiratory section (R) of the burrow on the left, and the drainage area (D) on the right. Water currents are represented by dotted arrows. Mucus (MS), produced from the ends of the clavulae, is shown ad- hering to the sand.

with increasing depth (Krumbein & Pettijohn, 1938), it follows that dis- posing of the water presents a greater problem than obtaining it. This is particularly true when the apical spines maintain an opening to the surface. The mechanics of the circulatory system of the burrow of M. ventricosa are, therefore, easier to understand if they are thought of as comprising a system for eliminating water from the burrow, rather than obtaining it. The fascioles play an important role in the circulation of respiratory currents within the burrow, and a description of their function is essential to an understanding of the burrowing habits of echinoids. Fascioles are comprised of numerous, small, modified spines calIed clavulae. These tightly packed spines form narrow bands. In M. ventricosa, one band encircles the petaloid area on the dorsal surface (the peripetalous fasciole), and another band encircles the epiplastronal area under the anal system (the subanal fasciole, which is incomplete in adult M. ventricosa). Each clavula has a thin shaft with two bands of cilia along each side and a bulb- 1969] Chesher: Biology of Meoma ventricosa 105 shaped distal portion which secretes a considerable quantity of mucus. The mucus adheres to sand grains and to the tips of the clavulae; thus are formed one continuous mucous "wall" that surrounds the petaloid area, and another that surrounds the epiplastronal area. These walls of mucus extend to the walls of the burrow and divide it into three main sections; a respiratory section encircled by the mucus of the peripetalous fasciole, an anal section isolated by the mucus of the subanal fasciole, and the remain- ing section, the locomotory section, where the spines used for movement and the tube-feet used for feeding are located. Water, propelled by the cilia of the clavulae, is moved from the petaloid area into the locomotory area where most of it drains out into the surrounding sand. Residual water is removed in the subanal drainage area. This process is shown diagrammatically in Figure 14. When the water passes through the peripetalous fasciole, some of it stays close to the test and flows over the ambitus to the ventral side. A large proportion, however, is diverted upwards, away from the test. The upward flow seems to be controlled by currents approaching the fasciole from the locomotory area, propelled by ciliary action along the lower parts of the spines. It is possible, however, that the fasciole may also contribute to the upward direction of these currents. The resultant upwardly directed current causes an area of drainage between the fasciole and the ambitus. Two other major drainage areas in the locomotory section of the burrow occur along the anterior ambitus and the median section of the plastron where opposing currents flow together. Burrowing movements in these areas probably increase the drainage facility of the burrow. The subanal fasciole provides the mechanism for ridding the burrow of surplus water, a problem that is apparently more serious for the juveniles, which burrow deeply and continuously in the sand. Water flows into this fasciole from the locomotive section of the burrow. Water approaching the fasciole from inside the fasciolar area directs the flow of water away from the test into the disturbed sand through which the animal has just passed. The adult urchins, which migrate to the surface of the sand at night and live near the surface of the sand during the day, have an incomplete subanal fasciole, and drainage from this area is less than in juveniles, which remain buried at all times (Fig. 3,A). Juveniles have a well-defined subanal fasciole and construct two small drainage tunnels behind them as they move through the sand. These tunnels are constructed by the joint effort of the spines within the subanal fasciole and the subanal tube-feet and aid drainage of the burrow by increasing the surface area of the burrow. The adult urchins do not construct drainage tunnels, and the subanal fasciole is degenerate as are the subanal tube-feet. 106 Bulletin of Marine Science [19(1) The movement of water within the burrow as determined in the laboratory was also examined in the field. A transparent, plastic dome was placed over a buried M. ventricosa to eliminate ambient current action. A long pipette was then introduced through a small orifice on the top of the dome and dark-green food dye was injected into the sand above the apical spines. After five minutes, the urchin was carefully excavated and major concentrations of dye in the surrounding sand located. The green dye was easily seen against the white sand, and the main concentration, indicating the major area of drainage of the burrow, was found between the ambitus and the peripetalous fasciole. Secondary concentrations were found at the anterior end of the animal, along the plastron, and a relatively minor amount near the subanal area. In subsequent experiments, this same pattern was found even when the period of time between injection of the food dye and excavation of the animal was extended to 30 minutes. The dye was seldom detected returning to the surface of the sand. When traces of dye did come to the surface, they were in the area directly above the lateral interambulacra, approximately over the peripetalous fasciole. Sand movement was found to be similar to that reported for Brissopsis atlantica (Chesher, 1968). The sand was moved posteriorly in the burrow by successive "waves" of spines. The metachronal rhythm of the spines forms waves which are shown diagrammatically in Figure 3. It should be noted that the areas which lack spines adjacent to the plastron are not major avenues of sand transport as suggested by Nichols (1959). At no time, when viewing buried animals through glass-bottomed aquaria, did these areas contain sand, and particles could be seen moving outward from the plastron area as shown in Figure 13.

ACKNOWLEDGMENTS A large portion of the staff and student body of the Institute of Marine Sciences contributed in various ways to the completion of this study, and I offer thanks to each of them. In particular, I thank Dr. F. M. Bayer for his supervision and direction of this study and Dr. H. B. Moore for his advice and contributions. Dr. and Mrs. W. A. Starck deserve special thanks for their continued help with the field operations. The urchins of Colombia were studied through the generosity of the Corporaci6n Aut6noma Regional de los Valles del Magdalena y del Sinu, Bogota, Colombia. The M. ventricosa of Panama were studied during ecological comparisons of the trans- isthmian echinoids sponsored by the Smithsonian Institution. The major portion of this study was conducted with the support of National Science Foundation Grant GB 2037. Part of the manuscript was revised during an N.S.F. Postdoctoral Fellowship at the Museum of Com- parative Zoology, Harvard University. The statistical analysis of the growth data was supported by a Milton Fund grant to Dr. H. B. Fell. 1969] Chesher: Biology of Meoma ventricosa 107

SUMARIO

CONTRIBUClONES A LA BIOLOGIA DE Meoma ventricosa (ECHINOIDEA: SPAT ANGOIDA) Se examinaron poblaciones de Meoma ventricosa procedentes de Santa Marta, Colombia, hasta Fort Lauderdale, Florida. Se usaron tecnicas de buceo para examinar los animales in situ. Se pueden delinear cuatro habitats grandes para M. ventricosa: hierba de Thalassia con bolsones de arena, zonas arenosas de aguas someras con hierba y manchas de coral, zonas de arrecifes coralinos y zonas arenosas de aguas profundas. De estos habitats, el segundo tenia las mayores poblaciones. Los ejemplares j6venes de M. ventricosa viven en areas de hierba 0 de coral, separados de los adultos y permanecen enterrados todo el tiempo. Ellos se trasladan a areas arenosas abiertas euando la concha alcanza alrededor de 60 mm de longitud. Los adultos salen de la arena por la noche, probablemente en respuesta a una disminuci6n en la concentraci6n del oxigeno en el ambiente. M. ventricosa forma pequenas manadas que permanecen unidas inde- finidamente y las cuales pueden moverse como una unidad, cuando no estan atrapadas en un bols6n de arena rodeado par hierba 0 coral. Los erizos aparentemente se congregan respondiendo a la presencia de otros individuos. M. ventricosa se alimenta con los pies ambulacrales especializados para la alimentaci6n, los cuales rodean la boca. La boca y el ana pueden dila- tarse hasta el maximo de la apertura en la concha. Experimentos alimen- ticios mostraron que la arena puede pasar por los intestinos en menos de 4 horas y que la eantidad promedio de alimentaei6n era 25 ml de arena por hora. Par la noche, cuando los animales estaban moviendose rapidamente, aproximadamente a mas de 65 ern por hora, la alimentaci6n cesaba. Cada M. ventricosa perturb a al ana alrededor de 48 metros cuadrados de substrato hasta una profundidad de 6 em. Parece que M. ventricosa mejora 0 mantiene su propio abastecimiento de nutrientes aumentando la porosidad del substrato. El alimento disponible no parece ser el factor mas importante que con- trola la proporci6n del crecimiento. En cambio, el contenido de cieno del substrato y el grado del cambio diario en la concentraci6n de oxigeno limita el tiempo de alimentaci6n y parecen ser los factores mas importantes que control an la proporci6n del erecimiento. El volumen de las g6nadas alcanz6 su maximo desarrollo en julio de 1965 y agosto de 1966. El desove continu6 desde entonces hasta prin- cipios de marzo. Tal parece que el desove sigue a una rapida maduraci6n 108 Bulletin of Marine Science [19(1)

de los huevos, probablemente en la noche y probablemente comprendiendo s6lo unos pocos individuos en cada desove. El pie ambulacral respiratorio y las ampul as tienen una fuerte corriente interna que circula en direcci6n opuesta a como 10 hacen las corrientes en la parte extern a de la concha. Este sistema de contra-corriente aumenta la eficiencia de las superficies respiratorias. Los fasciolos de M. ventricosa actuan como un mecanismo combinado de bomba y valvula para circular el agua a traves de la excavaci6n en que se entierran. EI agua entra a la excavaci6n a traves de los intersticios de la arena 0 a traves de una apertura mantenida por las espinas apicales y abandona la misma en lugares de drenaje fuera del area petaloidea de la concha. La excavaci6n est a dividida por el mucus de los fasciolos en tres secciones, cuyas funciones mas importantes son respiraci6n, 10comoci6n y drenaje. LITERATURE CITED BADER,R. G. 1952. A quantitative study of some physical, chemical, and biological va- riants of modern sediments. Univ. of Chicago, thesis No. 1531,76 pp. BOOLOOTIAN,R. A., A. C. GIESE, J. S. TUCKER,ANDA. FARMANFARMAIAN 1959. A contribution to the biology of a deep sea echinoid, Allocentrotus fragilis (Jackson). BioI. Bul!. mar. bioI. Lab., Woods Hole, 116(3): 362-372. BRATTSTROM,H. 1946. Observations on Brissopsis lyrifera (Forbes) in the Gullmar Fjord. Ark. Zoo!., 37 A(18): 1-27. BUCHANAN,J. B. 1966. The biology of Echinocardium corda tum (Echinodermata: Spatan- goidea) from different habitats. J. mar. bioI. Ass. U.K., 46(1): 97-114. 1967. Dispersion and demography of some infaunal echinoderm populations. Symp. zoo!. Soc. London, No. 20: 1-11. CHAET, A. B. 1966. The gamete-shedding substances of starfishes: a physiological-bio- chemical study. Amer. Zoo!., 6: 263-271. CHESHER, R. H. 1963. The morphology and function of the frontal ambulacrum of Moira atropos (Echinodea: Spatangoida). Bull. Mar. Sci. Gulf & Carib., 13(4): 549-573. 1968. The systematics of sympatric species in West Indian spatangoids. Stud. trop. Oceanogr. Miami, 7: viii + 168 pp., 35 pIs. ErcHELBAUM,E. 1910. Dber Nahrung und Ernahrungsorgane von Echinodermen. Wiss. Meeresunter., Abt. Kiel, NF, 11: 187-275. FERGUSON,J. C. 1967. An autoradiographic study of the ultization of free exogenous amino acids by starfishes. BioI. Bull. mar. bioI. Lab., Woods Hole, 133(2): 317-329. HOLLAND,N. D. 1967. Gametogenesis during the annual reproductive cycle in a cidaroid sea urchin (Stylocidaris affinis). BioI. Bull. mar. bioI. Lab., Woods Hole, 133: 578-590. 1969] Chesher: Biology of Meoma ventricasa 109

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