BULLETIN OF MARINE SCIENCE, 28(4): 659-666, 1978

ORIENTATION AND SOCIAL BEHAVIOR IN THE SUPRALITTORAL ISOPOD EXOTICA (CRUSTACEA: ONISCOIDEA)

James A. Farr

ABSTRACT is aggregative, tending to seek out conspecifics. It is hypothesized that Ligia must seek new shelters repeatedly with changing tides because of their restricted water requirements, and that attraction to con specifics already in a suitable habitat is an additional orientational mechanism to those external environmental factors influencing microhabitat selection. Experiments on object orientation demonstrated a strong tendency to move toward contrasting landmarks, the result being occupation of rocky areas on the shoreline. Brief descriptions of sexual and agonistic behavior are included.

It is generally held that terrestrial isopods, ties to facilitate location of wet, but not suborder Oniscoidea, are poorly adapted submerged, habitats. Because Ligia must physiologically for an existence on land, and occupy very wet areas, behavioral mecha- that their ability to minimize desiccation is nisms for water conservation may not be as a consequence of several behavioral adapta- prominent as those for finding water. tions resulting in their occupying cool, The present study was initiated to investi- humid areas (Edney, 1954, 1968; Warburg, gate the tendency of Ligia exotica to 1968). Three oniscoid genera, Porcellio, aggregate. They often cluster in large num- Oniscus, and Armadillidium, have been bers under rocks in the supralittoral zone, studied extensively in this regard. These but it is unknown if they orient to preferred are hygropositive and photonegative, microhabitats directly or if they actively and thus are able to find favorable micro- seek conspecifics. In the experiments on habitats (Abbott, 1918; Gunn, 1937; Wal- aggregation, oriented responses to environ- off, 1941; Warburg, 1968). A classic study mental stimuli were revealed, and these by Allee (1926) and subsequent work by were investigated further. Additionally, ob- Friedlander (1965) demonstrated that the servations on sexual and agonistic behavior tendency of land isopods to aggregate is an of L. exotica are also summarized herein. important mechanism for reducing desicca- tion. Orientation to external stimuli and MATERIALS AND METHODS attraction to conspecifics are both essential Ligia exotica were captured in rocky areas in counteracting the harshness of the emer- on the shore of Santa Rosa Sound at the gence from water. U.S. Environmental Protection Agency The oniscoid genus Ligia is much more Laboratory on Sabine Island, Escambia restricted to a wet environment than those County, Florida. Movements and abun- genera mentioned above. Of those genera dance were observed in the natural habitat. studied to date, Ligia is the most susceptible Most orientation work and some experiments to desiccation (Edney, 1951, 1954; Mayes on the tendency to aggregate were conducted and Holdich, 1975), and yet prolonged sub- outdoors at the EPA Laboratory in a mersion in seawater is also fatal (Hewitt, circular fiberglass tank, 2.4 m in diameter 1907; Tait, 1917; Barnes, 1932). Ligia, and 0.9-m high. The tank was placed in thus restricted to the immediate supralittoral an open area away from buildings and trees, zone, inhabit rocky areas at the water's edge. and the bottom was covered with 4.0 cm One would expect its orientational capabili- white beach sand kept moist with 15-20 %0 659 660 BULLETIN OF MARINE SCIENCE, VOL. 28, NO.4, 1978 seawater. Other experiments on aggregation In the second test, small glass aquaria were conducted in the laboratory in glass were used in the laboratory to examine aquaria, 50 cm X 30 cm, with 2.0 cm white further the hypothesis that L. exotica seek beach sand moistened with 20 %0 seawater. conspecifics. For each run, two animals I observed social behavior of animals in a were placed into an aquarium containing large glass aquarium, 1.2 m X 0.3 m with two clay saucers cleaned in tapwater. I re- sand and several rocks for shelter. Labora- corded whether the same or different saucers tory animals were maintained on a 12: 12 were selected as shelters. The probability photoperiod at 22-24°C and fed a dried that both animals would choose the same flake tropical fish food. saucer is p = 0.5. If the animals tend to Three experiments were conducted to be socially attracted to each other, a binomial determine if L. exotica aggregate because test would show the mean to be greater than they actively seek conspecifics or aggregate 0.5 N. Forty-eight pairs of animals were by chance in preferred microhabitats. In tested: 16 runs used two males, 16 used the first experiment 60 10.0-cm diameter two females, and 16 tested heterosexual red-clay saucers were arranged in a circle pairs. Different animals were used in each inside the circular outdoor tank so that an run. edge of each saucer rested on the lip of the Finally, a third experiment was designed adjacent saucer. For each of 10 replicates, to determine if chemoreception might be used 59 to 81 animals were released in the morn- in locating conspecifics. In each run a single ing in the center of the arena. After 24 h, was released into a small glass the number of animals residing underneath aquarium with two saucers. One saucer was each saucer was recorded. Following each placed in the stock aquarium with approxi- run, all animals were returned to the en- mately 75 adult animals for 24 h prior to its vironment and new ones captured for the use, and the other was cleaned in tapwater next run. prior to its use. In each run I recorded Two statistical tests were performed on whether the animal selected the clean or the distribution of animals in each replicate. the conditioned saucer; 25 animals of un- First, I tested whether they tended to determined sex were used. Preference for aggregate. If shelter seeking is random, the the conditioned saucer would demonstrate distribution of animals under the saucers an attraction to a chemical factor associated should be Poisson-distributed; deviation with the stock cage and hence, with con- from a Poisson distribution would show that specifics. The previous experiment with two they aggregated. However, merely demon- animals and two cleaned saucers, and earlier strating aggregation would not necessarily observations of single animals with one or demonstrate a tendency to seek can specifics, two cleaned saucers indicated no aversion to because the aggregations could result from cleaning with tapwater; all animals occupied orientation to an external stimulus rather a shelter. than to conspecifics. Therefore, I used In preliminary tests of aggregation in L. Rayleigh's test (Batschelet, 1972; Zar, exotica, it was discovered that they tended 1974) to test for a preferred directional to aggregate in the direction of a large over- orientation. Significant aggregation in the hanging tree visible from the floor of the absence of a preferred direction would sup- tank, and the circular tank had to be moved port the hypothesis that they are attracted to a more open location. Herrnkind (1968, to conspecifics. If the preferred direction 1972) discussed the importance of orienta- varied from test to test, then one cannot tion to areas of sharp optical contrast in separate orientation to a changing array of shore-living , particularly fiddler external stimuli from orientation to con- crabs of the genus Uca. Therefore, my tests specifics in different sections of the tank. were designed to discover if such object FARR: BEHAVIOR OF LlCIA EXOTICA 661

Table 1. Results of experiments on aggregation and directional preference in Ligia exotica. Significant X' values (d.f. = 5) indicate runs in which the animals tended to aggregate. Significant values of Rayleigh's r indicate preference for a single direction

X' for comparison Rayleigh's r No. animals with Poisson for length of Mean angle Run tested distribution mean vector of orientation

1 81 54.46** 0.1590 2 78 11.00 0.0719 3 67 17.76** 0.2302 4 58 312.13** 0.3368** 5 63 48.83** 0.2972** 6 73 94.21 ** 0.2286* 7 71 185.39** 0.1337 8 59 31.44** 0.2033 9 76 42.07':"~ 0.0109 10 75 27.03** 0.2688**

• significant at the 0.05 level. •• significant at the 0.005 level. orientation is exhibited by Ligia. Two ex- Ligia to aggregate. Runs 4, 5, 6, and 10 periments were conducted in the circular showed significant directional preferences, outdoor tank with 60 clay saucers arranged the preferred compass bearings ranging from in a circle as shelters. In each experiment, 124° to 330°. In four runs I observed ag- a piece of black vinyl plastic was used to gregation in a preferred direction, indicating cover a 40° section reaching from top to orientation to conspecifics only, to a variable bottom of the light blue walls of the tank. set of external stimuli, or both. In runs 1, A group of 54 to 81 animals was released 3, 7, 8, and 9, aggregation was exhibited in the center of the circle of saucers, and without any significant unimodal directional their distribution under the shelters was preference, and from this I conclude that analyzed to determine directional preference L. exotica actively seek conspecifics. In one with respect to the center of the black run, I observed neither aggregation nor pre- plastic. One experiment tested the location ferred direction. It should be noted that I of animals relative to the black plastic 15 tested only for preference to orient in a single to 30 min after their release. A second ex- direction. Conclusions that no directional periment examined their location 24 h after preference was exhibited could actually be their release. Each experiment consisted of false; different individuals could orient to eight runs, the piece of black plastic being different external stimuli, but the statistical placed in a different 45° segment of the test would show no preference. tank for each run. New animals were used In laboratory experiments with two ani- in every run. The V test (Batschelet, mals and two saucers, I observed a significant 1972; Zar, 1974) was used to determine if attraction to conspecifics. In 15 of 16 runs the animals were distributed in the expected with two males, both animals chose the same direction. saucer. When both were female, 14 of 16 pairs chose the same saucer. Finally, 13 of RESULTS 16 heterosexual pairs chose the same shelter. Experiments on Orientation and Aggregation A binomial test demonstrated that selection of shelter is not random, but influenced The results of the first aggregation ex- positively by the presence of conspecifics of periments are summarized in Table 1. In the same or opposite sex (0: < 0.01). nine of ten runs, the distribution of animals In tests allowing an animal to select a was significantly different from a Poisson conditioned or a clean shelter, 21 of 25 distribution, thus indicating a tendency for chose the conditioned shelter. Choice of 662 BULLETIN OF MARINE SCIENCE, VOL. 28, NO.4, ]978

Table 2. Object orientation of Ligia exotica to a Table 3. Distribution of Ligia exotica in relation dark 40° segment of a circular tank, 15 to 30 min to a dark 40° segment of a circular tank 24 h after after introduction to the arena. Significant values introduction to the arena. Significant values of the of the V statistic indicate degree of orientation in V statistic indicate degree of orientation in the di- the direction of the black plastic. All values of V rection of the black plastic are significant at the 0.001 level Mean Mean Direction direction Direction No. animals of black chosen by direction Run tested No. animals of black chosen by plastic animals V Run tested plastic animals V 1 63 0° 27° 16.3365** 1 56 0° 6° 47.3692 2 66 45° 63° 56.5127** 2 63 45° 41° 47.4948 3 59 90° 140° 25.8377** 3 81 90° 83° 54.0814 4 81 135° 216° 3.2792 4 69 135° 121 ° 51.4275 5 78 180° 180° 28.3857** 5 79 180° 182° 53.6976 6 60 225° 279° 15.7303** 6 76 225° 221° 60.4817 7 63 270° 356° 0.6029 7 67 2700 2640 59.6494 8 54 315° 224° -0.4691 8 69 315° 310° 55.1015 •• significant at the 0.00] level.

Observations on Social Behavior shelter by individual L. exotica is signifi- cantly influenced by a chemical factor Sexual behavior of L. exotica was similar associated with conspecifics (0: < 0.001), to that described by Kjennerud (1950) for as demonstrated by these experiments. the marine idotheoid isopod, ldothea ne- The results of the experiments on object glecta. Prior to copulation, a male mounts orientation in Ligia exotica are summarized a female and assumes amplexus, holding on in Tables 2 and 3. When the spatial distribu- to the female with the first pair of pereiopods tion of animals was recorded 15 to 30 min and straddling her with the remaining pairs. after their release, there was a significant More than 20 amplectic pairs were found in orientation to the dark contrasting area of the large stock cage, the outdoor circular the tank in every run (Table 2). These tank, and the smaller experimental cages, and results demonstrate that Ligia exhibits an in every case the male was larger than the immediate visual orientation toward a con- female. Carefoot (1973b) reported that trasting landmark when released into an males were always larger than the females open area. Direct observation of the animals in copulating pairs of L. pallasii. I observed immediately after their release verified this pairs in amplexus more than 24 h prior to response; most animals immediately turned copulation. to face the landmark and began running Copulation occurred immediately after the toward it. female moulted the posterior portion of her The results were not as dramatic when exoskeleton. The male shifted his abdomen the animals were allowed 24 h to choose a to one side of the female without releasing shelter (Table 3). In three of the eight his hold on her, moved his genital papilla runs, the animals were not significantly ori- forward, and copulated. This process was ented to the black plastic. A comparison of repeated several times, always alternating to the values of the V statistic in the 30 min the opposite side of the female from the and 24 h experiments reveals a much previous time. stronger initial response and a subsequent Three amplectic pairs were isolated to relaxation or waning of the response with determine the time between mating and re- time. Thus, the distribution of animals ap- lease of the young from the brood pouch. pears to be influenced initially by land- Nicholls (1931a) recorded incubation peri- marks, and other orientational cues become ods of 40 days in summer and 90 days in more important subsequently. winter for L. oceanica, and Carefoot FARR: BEHAVIOR OF L1GIA EXOTICA 663

(1973b) recorded incubation periods of 21 directed towards the opponent. A uropod to 28 days for L. pallasii in the laboratory shake was a response to contact of an at 20oe. I observed two females to release animal's posterior by another individual. young after 28 days and the third at 30 days, Frequently, uropod shaking was a response at 22°e. The number of young per brood by stationery feeders when approached by was not determined. another animal from the rear prior to con- I observed several hundred agonistic en- tact. counters in Ligia exotica, usually at feeding sites; a few involved intermale contests for Biting.-Only one biting incident was con- females. Typically, when food was placed firmed (an animal was wounded), but in the stock cage, the animals emerged from several incidents appeared to be attempted under rocks and approached the food site. or actual bites. Aggression was always observed among some Circling.- The most severe and least fre- animals, particularly between an animal quent type of aggression involved two ani- approaching the food and one already feed- mals attacking each other's uropods, and ing. All aggression involved physical contact; included attempted or actual biting and no distinguishable agonistic displays were uropod shaking. observed. The behavior was observed first- The winner of any agonistic encounter hand and on 8 mm movie film. Most direct could not be predicted on the basis of size observations were made while seated before or earlier arrival at the food site, although the aquarium without a blind. Some observa- this was not tested statistically. Often both tions were made through a small window to animals were observed feeding after a bout. the laboratory, and these revealed no qualita- In most cases, however, one animal either tive differences in agonistic behavior result- left the feeding site or moved to a different ing from the presence of an observer. I did position around the food. not determine the actual frequency of each On four occasions I observed intermale behavior. The following types of agonistic agonistic encounters over a female. In each behavior were observed. instance, a male and a female were in am- Leg beating.-This was the most frequently plexus, when a rival male approached and observed behavior and involved beating some attempted to dislodge the amplectic male part of the opponent with the pereiopods, from the female. The fighting involved at- particularly the anterior pairs. Leg beating tempted or actual biting. No female partici- was generally directed toward an opponent's pated actively in the fighting, though females pereiopods, head region, or uropods. Often appeared to turn to face the attacker. Three at a feeding site, adjacent animals pushed attackers were unsuccessful in supplanting each other with their legs, apparently in the original amplectic male. The fourth dis- response to an infringement of individual lodged the original male after a lengthy distance. encounter and assumed amplexus. During this encounter, the female was bitten and Antennal beating.-This form of aggression severely wounded on the dorsal surface of involved beating the pereiopods or uropods the abdomen. Within minutes after the new of an opponent with the antennae. It was male assumed amplexus, the pair was sur- clearly a more pronounced and violent ac- rounded by several smaller individuals who tion than typical sensory exploration ob- began to devour the female. They were served when animals would meet away from apparently attracted to her large open a food site. wound. Uropod shake.-This involved closing the In addition to these direct agonistic en- uropods together and violently shaking the counters, I have circumstantial evidence of abdomen. The closed uropods were generally aggression associated with amplectic or 664 BULLETIN OF MARINE SCIENCE, VOL. 28, NO.4, 1978 copulating pairs. Seven amplectic pairs were fishes (Barnes, 1934). Object orientation discovered during sampling in the first ag- is important, then, when tides force the gregation experiment described above: six animals to move from their shelters onto were alone under saucers, the seventh was shore. Such contrasting landmarks as trees, with one other individual. In a small glass dunes, and rocks are cues whereby animals aquarium containing five animals and one orient toward land and subsequently toward shelter, an amplectic pair was beneath the the rocky areas in which they live. Once in saucer and the remaining individuals re- a generally suitable area, object orientation mained outside on two occasions. These becomes less important, and other factors observations suggest that perhaps the male serve to orient Ligia to preferred micro- or both amplectic individuals aggressively habitats. An alternative is that they orient exclude other conspecifics from their im- to specific landmarks they have learned are mediate vicinity. In my large stock favorable microhabitats rather than in the aquarium where 15 to 30 animals were general direction of the shore. It is unknown beneath each rock, amplectic pairs were if landmark orientation is important in their observed frequently in the open areas of the nocturnal movements. Barnes (1932, 1935) cage. Apparently, population density was suggested that L. baudiniana, when sub- too high to permit aggressive exclusion of merged in seawater, orient away from the other animals, so the pairs moved to a less diffuse light of the open ocean, hence to- crowded open area. I found only two am- wards land. plectic pairs in nature, perhaps because When on land, Ligia orients down a slope they become more secretive during amplexus (Barnes, 1932), and thus remains close to and copulation. Those observed in the field water. Perttunen (1961) found L. italica were seen at night during their active oriented to areas of darkness and high period. humidity. This, too, would result in occupa- When food was placed in a small stock tion of areas near the water. Orientation aquarium with newly hatched juveniles, 1- to to a specific type of microhabitat is necessary 3-days-old, individuals fought at the food because Ligia tends to lose water in drier site in the same manner as adults. When a areas (Edney, 1951, 1954; Mayes and small piece of food was introduced, all move- Holdich, 1975). ments (leg beating, antennal beating, uropod Attraction to conspecifics may be another shakes, and attempted biting) appeared less influence on choice of shelter. Although coordinated than those of adults. Allee ( 1926) and Friedlander ( 1965) demonstrated that the tendency to aggregate DISCUSSION is important with regard to water conserva- tion in the more terrestrial genera of isopods, The above data suggest that several fac- one would not necessarily expect Ligia to be tors are important in spatial orientation of aggregative. Because Ligia is so restricted Ligia exotica. Object orientation, or orienta- to wet areas, behavioral mechanisms for tion to dark, contrasting areas, probably locating the immediate supralittoral zone guides the animals to rocky areas on the should be more important than other mecha- shore. My field observations suggest that nisms for reducing cutaneous water loss. L. exotica move with the tides, and they Although reduction of desiccation could be are frequently found trapped in air pockets a minor function of aggregative tendencies undcr rocks surrounded by water on an in- coming tide. These animals are subject to in Ligia, I suggest the following to be a drowning after prolonged submersion in more essential function. My observations on seawater (Hewitt, 1907; Tait, 1917; Barnes, L. exotica, and those of Barnes (1932) on 1932), and, being clumsy swimmers, are L. baudiniana and of Abbott (1939) on L. highly susceptible to by inshore occidentalis, suggest that the animals move FARR: BEHAVIOR OF UClA EXOTlCA 665 seaward with the ebbing tide as areas farther for growth and begin to produce eggs, and inland dry up, and move inland with the second, males must be larger than females incoming tide that covers their shelters with to reach the ground and be ambulatory dur- water. No shelter is permanent, and they ing amplexus. I suggest further that in must continually seek new habitats just competing for females, larger males have above the tide line. As individuals find new the advantage. Because males do fight for areas by the above orientational mechanisms females, copulating pairs minimize interfer- and by random movement, other conspecifics ence by separating from the group. Thus, can orient to those animals already under a amplectic pairs are usually found separated suitable rock. Thus, orientation to con- from aggregates of conspecifics. specifics could facilitate the search for In summary, Ligia exotica is attracted to favorable microhabitats. The tendency to conspecifics. Conservation of water does not aggregate could also facilitate finding mates, seem to be a function of this tendency to but this would be a result of, not a selection aggregate, as shown for more terrestrial pressure for, actively seeking conspecifics. genera (Allee, 1926; Friedlander, 1965; Because Ligia occurs in very high population Warburg, 1968), because Ligia is already densities, finding a suitable mate would ap- restricted to wet habitats. Orientation to pear never to be a serious problem. conspecifics facilitates finding new shelter Ligia tends to seek out conspecifics, but quickly as the tide changes and is merely appears to compete for food and mates. All an additional cue to those environmental species of Ligia studied to date feed pri- parameters already known to influence their marily on algae exposed by the ebbing tide location of favorable habitats. (Nicholls, 1931a; Barnes, 1932; Abbott, 1939; Carefoot, 1973a). Apparently, most ACKNOWLEDGMENTS feeding is restricted to nocturnal periods of I would like to thank the following people for .low tide, since they are mostly nocturnally their assistance in collecting animals and record- active (Nicholls, 1931a, 1931b; Abbott, ing data: C. Ashton, K. Brockman, J. Byers, J. 1939; Edney, 1953; Wilson, 1970; Mayes, Byers, T. Byers, R. Dime, and M. Redig. The and Holdich, 1975), and thus, food is avail- study benefitted greatly by my discussions with D. able only for limited periods of the day. Adkison, C. D'Asaro, P. Hamilton, and W. Herrn- kind. T. E. Bowman and D. Adkison aided me in Nicholls (1931b) reported that L. oceanica identification of specimens. The project was sup- feeds voraciously, "passing a continuous ported by EPA Grant No. R804458010 to Dr. stream through its alimentary canal, the C. N. D'Asaro, Faculty of Biology, University of feces containing nearly as much undigested West Florida. as indigestible food." Food is possibly a limiting factor in the environment, and as LITERA TURE CITED Ligia occurs in very high population densi- Abbott, C. H. 1918. Reactions of land isopods ties, competition for food manifested as to light. J. Exp. Zool. 27: 193-246. aggression is not unlikely. --. 1939. Shore isopods: niches occupied, In the only other report of aggression in and degrees of transition toward land life with special reference to the family Ligydidae. isopods, Kjennerud (1950) mentioned Proc. 7th Pacific Sci. Congr. 3: 505-511. briefly that larger male /dothea neglecta Allee, W. C. 1926. Studies in animal aggrega- may successfully displace a smaller male tions: causes and effects of bunching in land from amplexus with a female. Male Ligia isopods. J. Exp. Zoo I. 45: 255-277. Barnes, T. C. 1932. Salt requirements and space are characteristically larger than females orientation of the littoral isopod Ligia in Ber- (Carefoot, 1973b; Hewitt, 1907), and muda. BioI. Bull. 63: 496-504. Carefoot (1973b) suggested two possible --. 1934. Further observations on the salt requirements of Ligia in Bermuda. BioI. Bull. explanations for the disparity in size. First, 66: 124-132. at some point, females cease to utilize food --. 1935. Salt requirements and orientation 666 BULLETIN OF MARINE SCIENCE, VOL. 28, NO.4, 1978

of Ligia in Bermuda. III. BioI. Bull. 69: 259- Mayes, K. R. and D. M. Holdich. 1975. Water 268. exchange between woodlice and moist environ- Batschelet, E. 1972. Recent statistical methods ments, with particular reference to Oniscus for orientation data. Pages 61-91 in S. Galler, asel/us. Compo Biochem. Physioi. A, Compo K. Schmidt-Koenig, G. Jacobs, and R. Belle- Physioi. 51: 295-300. ville, eds. Animal orientation and navigation. Nicholls, A. G. 1931a. Studies of Ligia ocean- N.A.S.A., Washington, D.C. ica. I. A. Habitat and effect of change of en- Carefoot, T. H. 1973a. Feeding, food prefer- vironment on respiration. B. Observations on ence, and the uptake of food energy by the moulting and breeding. J. Mar. BioI. Assoc. supralittoral isopod Ligia pal/asii. Mar. BioI. U. K. 17; 655-673. 18: 228-236. 1931b. Studies on . II. 1973b. Studies on the growth, repro- The process of feeding, digestion, and absorp- duction, and life cycle of the supralittoral tion, with a description of the structure of the isopod . Mar. BioI. 18: 302-311. foregut. J. Mar. BioI. Assoc. U. K. 17: 675- Edney, E. B. 1951. The evaporation of water 708. from woodlice and the millipede Glomeris. Perttunen, V. 1961. Reactions de Ligia ita/ica 1. Exp. BioI. 28: 91-115. F. it la lumiere et it l'humidite de l'air. Vie et 1953. The temperature of woodlice in Milieu 12: 219-259. the sun. J. Exp. BioI. 30: 331-349. Tait, J. 1917. Experiments and observations on 1954. Woodlice and the land habitat. Crustacea. Proc. Roy. Soc. Edinburgh 37: BioI. Rev. 29: 185-219. 50-94. 1968. Transition from water to land in Waloff, N. 1941. The mechanisms of humidity isopod . Amer. Zooi. 8: 309-326. reactions of terrestrial isopods. 1. Exp. BioI. Friedlander, C. P. 1965. Aggregation in Olliscus 18: 115-135. asel/us Linn. Anim. Behav. 13; 342-346. Warburg, M. R. 1968. Behavioral adaptations Gunn, D. L. 1937. The humidity reactions of of terrestrial isopods. Amer. Zool. 8; 545- the , Porcellio scaber. J. Exp. BioI. 559. 14; 178-186. Wilson, W. J. 1970. Osmoregulatory capabili- Herrnkind, W. F. 1968. Adaptive visually-di- ties in isopods: and Ligia rected orientation in Uca pugilator. Amer. pallas;;. BioI. Bull. 138: 96-108. Zool. 8: 585-598. Zar, J. H. 1974. Biostatistical analysis. Pren- 1972. Orientation in shore-living ar- tice-Hail, New Jersey. 620 pp. thropods, especially the sand fiddler crab. Pages 1-59 in H. E. Winn and B. L. Olla, eds. DATEACCEPTED:August 22, 1977. Behavior of marine animals, vol. 1: inverte- brates. Plenum Press, New York. ADDRESS: Faculty of Biology, University of West Hewitt, C. G. 1907. Ligia. L. M. B. C. Memoirs Florida, Pensacola, Florida 32504. PRESENT AD- 14: 1-37. DRESS: Institut fiir Biologie, G esellschaft fiir Kjennerud, J. 1950. Ecological observations on Strahlen- und UmweltforscJumg, Ingolstiidter Idothea lleglecta. Univ. Bergen Arb. naturv. Landstraf3e 1, D-8042 Neuherberg bei Miinchell, R. 1950(7): 47 pp. West Germany.