Polychaeta: Syllidae)L

Reproduction and Larval Development of Typosyllis pulchra (Berkeley & Berkeley) (Polychaeta: Syllidae)l

ALBERT E. HEACOX 2

ABSTRACT: The reproductive biology of Typosyllis pulchra from the coast of Washington has been investigated based on observations of animals in the field and stolonization in the laboratory by both field-collected and cultured animals. Like most Syllinae, T. pulchra reproduces by stolonization, i.e., each individual produces 3-4 posterior, detachable, gamete-bearing stolons during consecutive 30-day intervals. Although some regenerating segments are in corporated into the stolons, in this species new stolons consist primarily of stock body segments. Reproductive animals occur in the field from late January through July; maximum reproductive activity is between April and June. Long days apparently promote reproduction, but lunar synchronization of spawning could not be demonstrated. Larval development is described based on light and scanning electron microscopy. Fertilization is external; developing larvae settle within 75 hr. The development of cephalic structures (eyes and antennae) is precocious com pared to other Syllinae that have been studied, and the sequence of para podium formation is unusual.

LITTLE INFORMATION IS AVAILABLE concern amica (Herpin 1925), Typosyllis variegata ing reproduction or larval development of (Cazaux 1969), and Typosyllis prolifera any syllid polychaete; there is almost none (Franke 1979). for species from the northeastern Pacific. This paper describes reproduction and de Most reports on western American syllids velopment in Typosyllis pulchra, based on are limited to descriptions of reproductive field observations on the coast of Wash individuals and contain little or no ad ington and laboratory spawning of collected ditional reproductive data (Pettibone 1954, and cultured animals. MacGinitie 1955, Pettibone 1963, Banse 1972). Brooding has been described in the exogonine Exogone lourei (Woodin 1974) MATERIALS AND METHODS and the eusylline Syllides japonica (Heacox and Schroeder 1978). Collection Larval development has been investigated in a number of syllids; many of these studies Typosyllis pulchra (Berkeley & Berkeley) concern brooding species of Exogoninae, was collected from the rocky intertidal, near Autolytinae, and Eusyllinae. All the Syllinae the Slip Point Light Station, Clallam Bay, studied have been European species: Washington, within the root-rhizome Typosyllis hyalina (Malaquin 1893), Syllis system of the marine angiosperm Phyllo spadix scouleri. Every 6-8 weeks, for a

1 This research was supported by The Lerner Fund period of 18 months, Phyllospadix samples for Marine Research and the Sigma Xi Research were collected, placed in plastic bags, packed Society. Manuscript accepted 19 May 1980. on ice, and transported to the laboratory in 2 Washington State University, Department of Zoology, Pullman, Washington 99163. Present address: Pullman, Washington, for sorting. Water Zoologisches Institut der Universitiit zu Koln, Weyertal temperature was recorded and samples for 119, 5 Koln 41, Federal Republic of Germany. salinity determination were taken at each 245 246 PACIFIC SCIENCE, Volume 34, July 1980

collection. Samples awaltmg sorting were with the exception of Dunaliella and kept in aerated plastic dishpans in artificial Phaeodactylum were macerated in a tissue seawater (Instant Ocean®, density 1.020, grinder and centrifuged before being added ASW) at 10 0 e. The syllids were sorted by to the cultures. Worms were routinely fed hand with the aid of a dissection microscope. once a week, and the water in the bowls was Animals were identified with Banse and changed 24 hr after feeding. Hobson (1974) and checked against the de Worms were determined to be reproduc scriptions of T. pulchra provided by Berkeley tive when gametes were observed in the pos and Berkeley (1948), Hartman (1968), and terior end or when signs of stolonization Banse (1972). (stolon eye spots; swimming setae) were pre sent. Animals showing signs of reproduction within 10 days of collection were considered Maintenance to have been reproductive in the field. Ten to fifteen individuals were kept in Reproductive individuals were separated out 4-inch covered fingerbowls with 150 ml and examined for stolon type, stolon seg ASW and a small amount of sand from the ment number, oocyte size in females, and original biotope. Animals were kept either at number of regenerating posterior segments. 8 ± 1°C with a 12L/12D light/dark cycle or The larval development was followed by at 10 ± 1°C with an 18L/6D light/dark cycle periodically anesthetizing larvae in 7.3 per

(Hauenschild 1972). Forty watts of indirect cent MgCl 2 and observing with a compound fluorescent lighting were used to initiate the microscope. light cycle. After the first hour, a step in crease in illumination was provided by the addition of 120 watts of direct fluorescent Scanning Electron Microscopy lighting. Light intensity was also decreased in a similar fashion at the onset of the last Some larvae were placed on 0.45-j.!m mil hour of light to simulate periods of dawn lipore or O.I-j.!m nucleopore filters, covered and dusk, respectively (Gidholm 1969). In with another filter, put in a filter holder, addition, a 15-watt light bulb was on during treated with 1500 NF3 units/ml ASW ovine the dark cycle of the five consecutive days hyaluronidase for 30 min (Atwood, Craw corresponding to the natural full moon of ford, and Braybrook 1975) to remove each month. mucus, and fixed in 2.5 percent glutaral Polychaetes in culture have been main dehyde in 0.2 M phosphate buffer containing tained on a variety of natural and artificial 0.14 M NaCI (pH 7.4). The specimens were foods (Muller 1962, Goerke 1971, Hauen then rinsed in 0.2 M phosphate buffer with schild 1972, Dean and Mazurkiewicz 1975). 0.3 M NaCI (pH 7.4) and postfixed in 2.0

The following foods were offered: frozen percent OS04 in 1.25 percent NaHC03 (pH spinach (Akesson 1967); powdered alfalfa 7.5) (Cloney and Florey 1968). Larvae were (D. Reish, personal communication); frozen then dehydrated through increasing concen Artemia (Hauenschild 1972); Tetramin®, a trations of ethanol, placed in an Omar SPC commercial dried fish food (Reish, personal 900 critical-point device and critical-point

communication); the green alga Dunaliella dried in CO2 (Anderson 1951). After coating (Dean and Mazurkiewicz 1975); the diatom with gold in a Technics V sputtering device, Phaeodactylum; and hyroid polyps (Hamond the specimens were examined with an ETEC 1974). Feeding trials were also made with VI Autoscan scanning electron microscope Tetra® squid flakes and the mussel Mytilus (SEM). californianus. The hydroid polyps Tubularia and Garveia were used in this study because of their abundance in the intertidal zone where T. pulchra was collected. All foods 3NF = National Formulary.

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5 mm

1 mm

FIGURE I. Adult Typosyllis pulchra showing regions of stolon formation and detail of anterior end (parapodia not shown). A, adult T. pulchra (S" segments involved in forming the first stolon; S2' segments involved in forming the second stolon; S3' segments involved in forming the third stolon); B, detail of anterior end (Pv, proventriculus).

...... !' • '1 ". 248 PACIFIC SCIENCE, Volume 34, July 1980

RESULTS immature animals (less than 50 segments, or 10 mm), many of which were probably over Description and Life Cycle looked during sorting. Water temperature in the field reached a low of 8°C in December. Adult Typosyllis pulchra have 76-110 se The water temperature gradually began to tigers and are 15-25 mm long and 0.5 mm increase in early March and reached a high wide, excluding parapodia and setae (Figure of 12°C in late July and August before be lA). Although Clallam Bay specimens fit the ginning its decline. During the peak repro general descriptions of Berkeley and Berke ductive period, water temperature was about ley (1948) and Banse (1972), they differ con 100e. sistently in some characteristics (Figure IE). For instance, the proventriculus begins in Stolon Formation setigers 9-11 and extends through 5-7 seg ments (rarely 8, Figure IE); Banse indicates Stolonization can first be recognized by a it is 8 or 9 segments long. The dorsal cirri are posterior color change-to blue or purple in slender and alternately long and short. Long females and to white or light pink in males cirri on midbody segments have 35-40 due to the accumulation of gametes. Stolons annuli, considerably fewer than the 50-70 consist of 22-30 setigers and have a chaeto recorded by Berkeley and Berkeley. Banse syllis head type (Malaquin 1893, Schroeder (1972) concludes that the "heavily pig and Hermans 1975) (Figures lA, 2). The mented papilla" of Berkeley and Berkeley is latter consists of a prostomial cleft, two pairs a small but distinct occipital flap. However, of eyes, a single pair of antennae, and a in Clallam Bay animals the pigmentation single pair of tentacular cirri. Laboratory may be almost completely lacking. Living produced and field-collected stolons are specimens vary from the "chocolate brown" similar in size. seen by Berkeley and Berkeley through In the laboratory, mature animals repro green-brown, bright green, blue-green, and duce by the sequential production of three or yellowish brown. Such variability occurs four stolons during consecutive 30-day peri even within the laboratory-reared offspring ods at 100e. Ten days after the release of the of a single pair of animals. previous stolon, gametes can again be seen Adults occur in the field throughout the in the 10-12 posteriormost segments; these year, although the percentage of adults and segments will be incorporated into the newly the number of reproductive individuals fluc forming stolon. Within 5 days of the first tuate. Between December and August only appearance of gametes, two pairs of eye adult individuals were found in the samples. spots form on a segment near the anterior Reproductive animals were first seen in late end of the sequence of gamete-bearing seg January and were found until July. Early in ments. The segment bearing the eye spots the reproductive season, stolonizing worms will become the head of the stolon. Between comprise 10-20 percent of the collected day 15 and day 25, the stolon changes little adults; the percentage gradually increases externally. Shortly after day 25, bundles of through the spring until May and June when capillary swimming setae erupt from the reproductive animals make up 40-60 percent notopodia of each stolon segment except the of a collection. Animals collected after July head and the 3-4 terminal segments. These were never reproductive in the field, and bundles of about 20 setae attain their full adults collected in August and September length (3 mm) within 48 hr. Soon thereafter showed high mortality when maintained in the stolon commences swimming move the laboratory. The number of animals col ments, which are independent of the stock. It lected, as well as the percentage of adults, eventually breaks free, swims to the surface, declines from late summer through October. and spawns. The scarcity of worms in the fall is believed Before stolonization is complete, the stock to be due to the higher proportion of small, begins to regenerate new posterior segments.

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FIGURE 2. Scanning electron micrograph ofstolon chaetosyllis head (A, antenna; E, eye; Tc, tentacular cirrus).

Immediately after stolon separation, four or tures. The long-day cycle (l8Lj6D) is similar five newly formed segments can be seen at to natural light conditions in the field during the posterior end of the stock. In all, about the late spring peak reproductive period; at ten segments are regenerated. This means lOoe, it proved suitable for raising larvae the worm must use additional stock seg and maintaining reproductive worms. ments to form the subsequent stolon Nonreproductive adults (determined by size) (average, 25 ± 3 segments, Figure lA). taken from the field and subjected to these conditions often became reproductive even if Culture Results collected in the late fall or winter. Once animals had become reproductive, they Animals that were determined to be repro would remain so for at least two consecutive ductive in the field could be kept in their stolonizations. reproductive condition by either the short The step increase following the initiation day, low-temperature cycle or the long-day, of the light seemed to stimulate stolon re high-temperature cycle. However, the short lease. Most stolons were found to separate, day regime neither brought nonreproductive swim, and spawn soon after the end of the winter animals to maturity nor did it main dawning period, but detailed records were tian reproductivity in the laboratory cul- not kept. Although a few stolons would 250 PACIFIC SCIENCE, Volume 34, July 1980 begin swimming later in the day, none were TABLE I found to separate and swim during the dusk FOOD AND FEEDING RESPONSE or dark portions of the cycle. The artificial lunar cycle produced no FOOD RESPONSE recognizable synchronization of stolon re lease or spawning. Both field-collected and Duna/ie//a lerlio/ecla (Chlorophyta) * Phaeodacly/um Iricornulum (Diatomacae) * laboratory-reared animals appeared to Tubu/aria sp. (Hydrozoa) spawn randomly. This apparent randomness Garveia sp. (Hydrozoa) may be an artifact of the relatively small Arlemia (adults, frozen) (Crustacea) + number of animals in the laboratory at any Myli/us ca/ifornianus (Bivalvia) Powdered alfalfa one time. Usually, no more than two or Tetramin@ + three animals spawned on anyone day, and Tetra@ squid flakes + reproduction was evenly spread over the Spinach (frozen) entire month. *Although no positive feeding response was observed, some larvae were Potential food items were placed on the raised through adulthood on this alga. bottom of the culture dishes, and responses were recorded. A positive response was re corded when an animal approached the food, everted its proboscis, and the pro stages are always found on the bottom of the ventriculus exhibited a pumping movement. culture bowls. It appears that the eggs sink The results are summarized in Table 1. soon after fertilization. A number of animals were raised solely on the two algae; however, these cultures always Cleavage through Gastrulation contained a number of protozoa and occa sionally some other small animals that could Fertilization produces a very thin fertiliza also have served as food items. After the tion membrane. Within 15 min, two polar initial testing, cultures were generally fed on bodies are released; they remain within the a combination of Dunaliella, Phaeodactylum, fertilization membrane for a time. No polar Artmeia, and both Tetra® products. bodies were ever observed attached to the This light-temperature regime and feed embryo after the four-cell stage. Cleavage ing schedule allowed the maintenance of is spiral, holoblastic, and unequal. Polar adults and the culture of larvae. Worms were lobe formation, reported in some syllids successively raised from larvae through three (Schneider 1914, Allen 1964), was never ob generations. The third generation did not served. Early blastulae are found as soon as reproduce as expected, however, and the 4 hr after fertilization, spinning on the cultures eventually died out. bottom of the culture dishes. An equatorial band of cilia penetrates the fertilization membrane; hatching does not occur. Gastru Spawning and Fertilization lation is by epiboly and occurs within the Spawning takes place near the water sur next 4 hr. face, usually within the first hour after stolon release. There is no obvious mating behavior Trochophore such as has been observed in Autolvtus (Gidholm 1965). Both male and female game The first trochophore larvae can be ob tes are shed through nephridiopores at the served after 24 hr and are nearly spherical base of each parapodium. Freshly spawned (90 x 100 ).lm). They have a long apical tuft, oocytes float on the surface for about 24 a telotroch composed of several short cilia, hr if they remain unfertilized. A similar ob and a single pair of eye spots. The eyes are servation was made by Herpin (1925) for reddish, bean-shaped structures located on Syllis amica. Fertilization also appears to the dorso-lateral surface midway between take place at the surface, but early cleavage the prototroch and the apical tuft. Just an-

,. Reproduction and Larval Development of T. pulchra-HEAcox 251 A

Sp 50um

50 pm

FIGURE 3. A, late trocophore larva with equatorial prototroch (AT, apical ciliary tuft; E, eye spot; Sp, Iight colored spot; T, telotroch); B, metatrochophore larva (S, spinelike protrusion; Sp, light-colored spots). 252 PACIFIC SCIENCE, Volume 34, July 1980

terior to the eyes is a pair of light-colored reach 200 Jlm in length and change shape. spots in the area that eventualIy gives rise to Both these changes are due in part to the the lateral antennae (Figure 3A). narrowing of the episphere, which may be During the next 24 hr, the larvae elongate due in part to yolk consumption. The larvae slightly and taper at the posterior end, prior now appear to have a head and neck. The to segment formation and initiation of the prototroch has disappeared, and only a few metatrochophore stage. cilia project laterally in the region of the eyes. Several additional spines have also ap peared in place of the apical cilia, as well as Metatrochophore along the lateral portion of the head and The slightly more elongate (115 Jlm) meta neck region. By this time the purplish yolk trochophore can be recognized by a pos has disappeared; the larvae are translucent. terior segment separating the episphere and The pharynx is 60 Jlm long and occupies pygidium. The apical tuft becomes a diffuse most of the head and neck region; move band of cilia bordering the anterior end of ments of this organ indicate that the animal the episphere. Within this apical band there begins feeding at this time. Two budlike are also two spinelike projections, which caudal cirri are now present on the have been regarded as tactile by Herpin pygidium. (1925). The prototroch is stilI prominent; it divides the episphere transversely into ap Setigerous Larvae proximately equal halves. EventualIy, the anterior half will develop into the pros The first setigerous larva (Figure 4) is tomium, while the posterior half of the about 300 Jlm long and appears early in the episphere will become the peristomium. third week. The first pair of parapodia ap Posteriorly the pygidial segment has some pears as fleshy lateral outgrowths from the short cilia, two spines, and two light-colored second larval segment following the epi spots. The latter are similar in size and shape sphere. Each parapod is supported by a to those anterior to the eyes. The pygidial blunt aciculum and contains a single simple cirri arise near these spots. The mouth is a notoseta (Figure 5). Soon afterward, one transverse slitlike opening, surrounded by compound seta appears in each parapodium, cilia, and located in the center of the ventral followed shortly thereafter by a second surface of the episphere. At this stage the (Figures 5, 6). Two lateral antennal buds pharynx and the gut are well developed, but now appear on the head region. In addition, there is no indication that the larvae have the median antenna is beginning to form begun to feed. A great deal of yolk is still between the eyes. Toward the end of the present. The neurotroch is a 20-Jlm wide third week the second pair of eyes forms. ventral band of cilia that extends posteriorly They are smaller than, and posterior and from the mouth to near the end of the medial to, the first pair. The caudal cirri are pygidium. not quite 35 Jlm long. The metatrochophore adds a second seg By the fourth week another segment with ment and settles within 75 hr of fertilization, pm"apodia is added, and both median and when it is about 130 Jlm long (Figure 3B). lateral antennae elongate. At the end of the The apical cilia are more diffuse, and a fourth week parapodia form on segment one second pair of spinelike protrusions projects and a fourth segment begins to appear. In laterally (one near each eye). Although the the fifth week larvae are 375 Jlm long and prototroch is still present, the gliding motion have four well-developed eyes, a median an exhibited by these larvae is due to the tenna with five or six articles, and lateral neurotroch. Each segment has two or three antennae with one complete article. The epi spines that protrude in a posterolateral sphere cannot be differentiated into an an direction. terior prostomium and a posterior peris During the subsequent 48 hr, the larvae tomium. The peristomium forms in the neck Reproduction and Larval Development of T. pulchra-HEAcox 253

100 ~m

FIGURE 4. One setiger larva (CC, caudal cirrus; MA, median antenna).

2~m

FIGURE 5. Illustration of larval setae on parapod of a one setiger larva. region and becomes a presetigerous segment six. A second pair of tentacular cirri has with a pair of tentacular cirri. The next three formed on the peristomium, and the first has segments have well-developed parapodia (al two to three articles. The prostomium has though those of segment one are smaller) developed small palps. Growth proceeds by and setae, and the better-developed para the addition of segments at the posterior podia have rudiments of dorsal cirri. until the adult number of 80-100 segments is Segment four is beginning parapodium for reached in 6-9 months, at which time mation, but setae are absent. The caudal animals become sexually mature. cirri include two articles (Figure 7). By the eighth week the larvae consists of 6-10 setigers and begin to resemble adults. DISCUSSION The more anterior setigers are well devel oped and their dorsal cirri have up to ten Reproduction articles. The median antenna has eight or ten Correlation of field observations and labo articles, and the lateral antennae have up to ratory cultures makes possible the prediction 254 PACIFIC SCIENCE, Volume 34, July 1980

FIGURE 6. Scanning electron micrograph of larval compound seta.

100 pm

FIGURE 7. Three-setiger larva (LA, lateral antenna; Te, tentacular cirrus). of an annual history for Typosyllis pulchra. been reported to breed all year (Schroeder Most larvae are spawned in the spring and, and Hermans 1975), most have a distinct after a short period of swimming, settle, reproductive season. Synchronization of metamorphose, and develop into adults reproduction within this short reproductive during the subsequent 8 months. Once ma season has been correlated with a number of turity is reached, the adult produces stolons environmental factors, including a spring during three or four consecutive 3D-day peri plankton bloom (Thorson 1946, Barnes ods. After the final spawning, the adults die. 1963), temperature (Orton 1920, Okada Although a number of polychaetes have 1941, Dales 1950, Bhaud 1967, 1972), the Reproduction and Larval Development of T. pu/chra-HEAcoX 255

lunar cycle (Clark and Hess 1940, Korringa ductive season, but higher temperature may 1947, 1957, Hauenschild 1960, Hauenschild, be needed to support peak reproduction. Fischer, and Hoffman 1968), and salinity This response to increasing day length ap (Aiyar 1931, 1933, Smith 1964, Akesson pears to be very sensitive; animals respond 1970). to very slight changes in day length. Temperature has been shown to influence While temperature and day length may maturation in several polychaetes. Durchon regulate breeding season, the proximate (1959) has shown that stolonization and causes for synchronized spawning are gametogenesis in Syllis amica can be induced thought to be, in some cases, lunar or tidal if worms are maintained for a month at cycles. The laboratory population of temperatures higher than those in the field. Typosyllis pulchra released stolons and Higher laboratory temperatures have also spawned in the early morning hours of the been shown to accelerate maturation in artificial light cycle. Changes in light in Glycera dibranchiata (Simpson 1962) and tensity, which occur at dawn and dusk, in Hydroides dianthus (Turner and Hanks 1960, duced swimming in stolons of Autolytus ed Leone 1970). The effects of day length are wardsi (Gidholm 1969). No response to the still virtually unknown. Sarvala (1971) in change in light intensity at dusk was ob dicates that spawning of Antinoella sarsi at served in T. pulchra; most started swimming different localities corresponds to the at dawn. Changes in light intensity may also breakup of arctic ice, which varies light and be implicated in the swarming of the epigam temperature. However, Sarvala feels that ous eusylline syllids Pionosyllis lamelligera light intensity or day length is more impor and Eusyllis blomstrandi. These swarms tant than temperature. Garwood (unpub seemed to be influenced by the presence of lished, from Olive and Clark 1978) has direct sunlight; they disappeared when the found that moderately long days accelerate sun was obscured by a cloud (Herpin 1925). the growth of vitellogenic oocytes while long Typosyllis prolifera can be entrained to an days inhibit vitellogenesis in Harmothoe im artificial lunar cycle. Animals spawned bricata. Early oocytes seem not to be af throughout the month, but the greatest fected. Franke (1979) has shown that both number of worms spawned just prior to the day length and temperature affect stolon artificial full moon (Franke 1979). However, production in Typosyllis prolifera. The lar no more than 10 percent of this laboratory gest number of stolons is produced under population spawned on a given day. If a conditions of high temperature (20°C) and similar response were given by T. pulchra, it long (18-hr) days. Decreasing temperature may have gone unobserved because of the (to l20 C) or shortening day length (to 10 hr) small number of animals kept in the labo reduces stolon formation about 50 percent; ratory. Lunar synchronization of spawning low temperatures and short days inhibit thus cannot be discounted. reproduction. Temperature and day length were not Larval Development changed independently for Typosyllis pulchra. However, winter animals would Larval development in Typosyllis pulchra become reproductive when maintained at is similar to that in other syIIids, especially higher temperature (10°C) and long days (16 the Syllinae (Malaquin 1893, Herpin 1925, hr). Stolons and gametes can first be seen in Cazaux 1969, Franke 1979). The differences the field population during late January, relate primarily to the timing and duration before water temperature begins to rise. of larval stages, the precocious development Peak reproduction is not reached until both of cephalic structures, and the sequence of day length and temperature have increased. parapodium formation. Differences in the This situation is similar to that of T. pro timing of larval development are probably lifera (Franke 1979). Increasing day length related to the temperatures at which larvae may be responsible for initiating the repro- were raised. 256 PACIFIC SCIENCE, Volume 34, July 1980

Although the larvae of the Typosyllis metatrochophore larva apparently develop pulchra swim, it is not known whether the in a normal sequence, in Typosyllis pulchra larvae actually contribute to the plankton. the parapodia develop in an unusual se No syllid larva is known to have an extended quence. As with Syllis amica (Herpin 1925) phase of pelagic development. Extensive and T. variegata (Cazaux 1969), the first pair sampling by Thorson (1946) and Bhaud of parapodia forms on the second segment (1972) has shown few syllids to be present in behind the episphere. In T. pulchra this hap the plankton. pens prior to external signs of peristomium The development of cilia, which precedes formation. This is different from T. prolifera, the swimming larval phase, appears to be where Franke (1979) shows the first setiger related to the reproductive strategy of the ous larva with parapodia on the first postep subfamily. All Syllinae and most Eusyllinae isphere segment. In T. pulchra an additional fertilize eggs in the sea and have a relatively segment forms and develops parapodia long swimming phase; larvae develop cilia before parapodia develop in the first post early during development. In Typosyllis episphere segment. Neither Herpin nor pulchra, cilia develop during the blastula Cazaux make clear the fate of the first post stage; other Syllinae develop cilia at least episphere segment. In S. amica and T. prior to the trochophore stage (Malaquin variegata this larval segment may give rise to 1893, Herpin 1925, Cazaux 1969). The the peristomium. Cazaux clearly shows the Exogoninae and some Eusyllinae [e.g., best-developed parapodia immediately pos Parapionosyllis gestans (Cazaux 1969)], terior to the peristomial segment in older which brood their young until some seti setigerous larvae. The episphere of T. gerous segments form, have neither cilia nor pulchra gives rise to both prostomium and a swimming phase. In contrast, T. prolifera peristomium, while all the setigerous seg larvae are ciliated but lack a swimming ments originate from the former hyposphere. phase; early development takes place within This indicates a fundamental difference be an extraembryonic membrane (Franke tween the peristomium and the setigerous 1979). Allen (1964) indicates that the preco segments. cious development of larval cilia in Autolytus fasciatus, when compared to other auto Iytids, represents a probable swimming stage. ACKNOWLEDGMENTS Larval cilia also seem to be responsible for the formation of certain larval structures. The author wishes to thank Paul Spinelike processes, found in the apical Schroeder, Howard Hosick, and Stacia ciliary band of Typosyllis pulchra and many Moffet (Department of Zoology, Washing other syllids (Malaquin 1893, Herpin 1925, ton State University) for their advice, sug Okada 1930, Dales 1950, Allen 1964, gestions, and criticisms. Additional thanks Cazaux 1969), are not found in the ex are extended to Karl Banse (Department of ogonines. Allen (1964) indicates that these Oceanography, University of Washington) structures in Autolytus fasciatus are tufts of and Fred Piltz (The Allan Hancock cilia. Foundation, University of Southern Development of head structures in Typo California) for confirming the species identi syllis pulchra is somewhat precocious. The fication, to Joyce Lewin (Department of median antenna, the lateral antennae, and Oceanography, University of Washington) the second pair of eyes differentiate in the for supplying the algal cultures, to John first setigerous larva. These structures are Singleton (Graphics, Washington State already well developed by the three- and University) for his illustrations, and to four-setiger stage, when they are first ap David Bentley and Joyce Davis (Electron pearing in other Syllinae (Cazaux 1969). Microscope Center, Washington State Although segments in the presetigerous University). Reproduction and Larval Development of T. pulchra-HEAcoX 257

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M5f"±ti . i¥ 5..£ Reproduction and Larval Development of T. puichra-HEACOX 259

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