Pacific Science (1980), vol. 34, no. 2© 1981 by The University Press of Hawaii. All rights reserved

The Annual Cycle of Oogenesis, Spawning, and Larval Settlement of theEchiuran Listriolobus pelodes off Southern California!

JOHN F. PILGER2

ABSTRACT: Listriolobus pelodes lives in aggregated populations in fine-grained sediments along the mainland shelf from northern California to BajaCalifornia, Mexico. This echiuran forms U-shaped burrows and uses its pro-boscis to feed on the uppermost layer of sediment deposited around the burrowapertures. The bacterial flora of the sediment may be an important food source.Commensals in the burrow include a polychaete, a pinnixid crab, and a smallbivalve.

The annual reproductive cycle of a population off Palos Verdes, California,is defined in terms of coelomic oocyte dynamics, spawning, and larval settle-ment. Small oocytes are released from the gonad through most of the year butfully grown oocytes are present only from mid-fall through spring. It is estimatedthat the coelomic phase of oogenesis lasts about 5 months. Fully grown oocytesare removed from the coelomic fluid in the germinal vesicle stage and accumu-late in the storage organs until spawning. Spawning takes place in winter andspring a(ld individuals are spawned out by summer. An annual influx of smalljuveniles into the population occurs in late winter and spring. The newly settledjuveniles reach sexual maturity when they are 6 months to 1 year old.

echiurans in all aspects except size. In 1970,during an investigation of a large oil spillwhich occurred at Santa Barbara, it wasfound that the number of L. pelodes haddecreased dramatically (Fauchald 1971).Populations of L. pelodes are found in otherareas off the southern California coast(Fauchald and Jones 1976; Green and Smith1975). All of these populations share threecharacteristics: (I) L. pelodes is a dominantmacroinvertebrate, (2) they are highly ag-gregated, and (3) they are located in areascomposed of fine-grained sediments with ahigh organic content.

In spite of its prominence in localizedbenthic communities, surprisingly little isknown about the biology of Listriolobuspelodes. The purpose of this paper is toprovide a compendium of information aboutthe natural history and behavior of Listriolo-bus pelodes and, further, to describe itsreproductive biology in terms of coelomicoocyte dynamics, spawning, and larval set-tlement. Reproductive cycles have beenstudied in related phyla such as the annelids

129

Listriolobus pelodes (Fisher 1946) is a deposit-feeding echiuran found in 18-155 m depthsalong the west coast of North America fromnorthern California to Baja California,Mexico. Barnard and Hartman (1959) de-scribed a unique area of fine-grained sedi-ments dominated by this animal near SantaBarbara, California. The more peripherallylocated members of this population wereconsiderably smaller than the centrallylocated ones. These "small phase" echiuranswere considered to be similar to the larger

1 This research was supported in part by BiomedicalResearch Support Grants RR07012-09, RR07012-10,and 5S07 RR07012-10 from the Division of ResearchResources, Bureau of Health Professions, Educationand Manpower Training, National Institutes of Health.Scientific Contribution No. 42. Catalina Marine ScienceCenter, University of Southern California, P. O. Box 398,A valon. California 90704. Scientific Contribution No.55. Smithsonian Institution, Fort Pierce Bureau-HarborBranch Foundation, Inc. Consortium, Fort Pierce,Florida 33450. Manuscript accepted 4 September 1979.

2 Smithsonian Institution, Fort Pierce Bureau, RouteI, Box 194-C, Fort Pierce, Florida 33450.

130 PACIFIC SCIENCE, Volume 34, April 1980

White'sPoint

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FIGURE I. The collecting site, station 6C, at White's Point, California. Inset of California showing the locationof the White's Point area.

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Echiuran Reproduction off Southern California-PILGER

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FIGURE 2. Regression of body volume against wet body weight of L. pelodes collected from station 6C.

(see Schroeder and Hermans 1975 for areview; Olive 1977, 1978) and sipunculans(see Rice 1975 for a review; Gibbs 1976),but they have never been investigated in theEchiura. It is hoped that this informationwill provide a basis from which furtherstudies of this interesting echiuran willemerge.

METHODS

Specimens of L. pelodes were collectedfrom a depth of 60 m at station 6C of theLos Angeles County Sanitation District,

near White's Point, California (33°42.5' N,118°20' W; Figure I). Supplementary in-formation for certain aspects of this studywas obtained by using large specimens col-lected from the Santa Barbara, California,L. pelodes population which was describedby Barnard and Hartman (1959; 34°23' N,119°38' W). Live animals and sediment wereobtained with a Shipek grab or box corerand maintained in flow-through seawateraquariums in a laboratory at the CatalinaMarine Science Center, University of South-ern California.

Adults of L. pe/odes are poor burrowersand will die if a burrow is not constructed.

.,

132 PACIFIC SCIENCE, Volume 34, April 1980

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ing of aspects of the animal's behavior whichtake place within the burrow.

Diameter of coelomic oocytes was used asthe primary index of gametogenic activity.On a monthly basis from January 1975through December 1976, a sample of coel-omic fluid was withdrawn with a syringe from5 females; 40 oocytes were measured in eachspecimen. The frequency distribution of thesediameters was plotted on a time scale.

Differentiated gametes accumulate in 2pairs of storage organs (modified nephridia)until spawning. These organs become greatlyenlarged by the accumulation of gameteswithin them. A relative decrease in the volumeof these organs can indicate the time ofspawning. For each individual, the 4 organswere measured and their total volume calcu-lated. This volume was divided by the ani-mal's wet body weight to correct for differ-ences in individual size. It was not possibleto make these measurements on the speci-mens from White's Point because they werecollected as part of a County Sanitation Dis-trict study which precluded their dissection .To get some idea of the spawning period,however, data were obtained from specimenscollected from Santa Barbara, California, asreported by Barnard and Hartman (1959) andothers (Pilger 1977).

The size-frequency distribution of echiu-rans in the samples taken at station 6Cindicated the period of larval settlement.Wet body weight was used as an index ofsize. This measurement was found to bedirectly related to body volume (Figure 2)and could be determined accurately andrapidly.

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FIGURE 3. Ventral view of Lislriolobus pelodes. 1m,longitudinal muscle band; m, mouth; n, nephridiopores;nl, anterior nerve loop; p, proboscis; S, setae; vnc,ventral nerve cord on mid-ventral muscle band. Scaleequals 5 mm.

The number of casualties from this problemwas minimized by artificially constructingU-shaped burrows for some, and by main-taining others in glass or plastic tubing andproviding sediment for feeding. Burrows innarrow glass-sided boxes filled with mudfacilitated the observation and understand-

RESULTS

Natural History Observations

The body of Listriolobus pelodes (Figure 3)is subspherical to ovoid and measures up to4 em long and 2 to 3 em wide. A green pig-ment usually is present on the anterior andposterior ends of the body and 8 regularly-spaced longitudinal muscle bands are visiblein the body wall. The mouth is located

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Echiuran Reproduction off Southern California-PILGER 133

ventrally at the base of the dorsoventrallyflattened, highly extensible proboscis. Twohooked setae straddle the ventral midlinebehind the mouth. A pair of nephridioporesopen on each side of the ventral nerve cordposterior to the setae.

Using a box corer, 10 intact Listriolobuspelodes burrows were collected from SantaBarbara, California. Careful examination ofthese burrows showed all of them to beU-shaped with exactly 2 openings to thesurface. Peristaltic contractions of the bodypump respiratory water through the burrow.The anal vesicles (paired hind-gut diver-ticulae) intermittently "inhale" and "exhale"portions of this water.

Listriolobus feeds on deposited sedimentthat surrounds the burrow apertures. Whilefeeding, the body remains within the burrowand the proboscis extends onto the substratewith its ventral side up. The top layer ofsediment is picked up by the proboscis andtransported by ventral cilia to the mouth.Laboratory observations showed that certainareas of sediment are grazed while others aredisregarded. This may indicate that somedegree of qualitative discrimination takesplace in food selection.

Fecal pellets (0.5 x 1.0 mm ellipsoids) re-main in the burrow for a while after theirrelease. The combined effect of the watercurrents from the body's peristaltic contrac-tions and the "exhalations" from the analvesicles intermittently expels the pellets fromthe burrow. The feces accumulate on thesediment around the burrow apertures andgive rise to the hummocky topography of anL. pelodes bed (R. Given, personal com-munication). Since these pellets typically arereingested after a short exposure on thesediment, a rapidly regenerating food re-source is implied (e.g., bacteria and associatedmicroorganisms) .

The proboscis is highly extensi ble and largespecimens of L. pelodes have been observedto feed on the sediment as far as 20 cm fromthe burrow aperture. L. pelodes intermit-tently turns around in its burrow, thusfeeding on the sediment surrounding bothburrow apertures. These observations in-dicate that up to 0.25 m2 of substrate surface

is available for feeding by individual echiu-rans and imply that in dense L. pelodespopulations (approximately 100 individuals'm- 2) all of the sediment surface is regularlygrazed. Clearly, the potential impact of thepresence of L. pelodes on sediment reworkingand the trophic structure of the benthiccommunity is great.

At least 3 commensal organisms werefound to be living in the burrow of Listrio-lobus pelodes: the polychaete Hesperonoelaevis (Hartman 1961), the pinnotherid crabPinnixa schmitti, Rathbun 1918, and thebivalve Mysella tumida (Carpenter 1864).Although there does not appear to be anydirect interaction between these commensalsand the echiuran, the burrow may affordthem some protection, and nutritional benefitmay be derived from the water and asso-ciated organisms which are pumped throughit (Fisher and MacGinitie 1928). A peritri-chous ciliate was discovered in the coelomicfluid of a few specimens and a helminthparasite was found embedded in the pro-boscis musculature of another. Neither ofthese was identified further.

Oogenesis

Echiuran oogenesis may be divided into 3distinct phases. The oocytes begin theirdifferentiation in the gonadal phase. Theyenter the second, or coelomic, phase whenthey detach from the gonad and continuetheir growth in the coelomic fluid. Finally,as germinal vesicles, they enter the storagephase when they are removed from thecoelomic fluid and accumulated in the modi-fied nephridia.

In Listriolobus pelodes the gonad is situatedon the ventral blood vessel in the posteriorregion of the body (Figure 4). The bloodvessel is attached to and follows the ventralnerve cord posteriorally. Near the rectum thevessel separates from the nerve and attachesto the intestinal caecum. The germ cells arisefrom the tissue surrounding the blood vesselin this region.

Small primary oocytes (5-7 f.lm) are re-leased from the gonad in clusters of 20 to 30cells (Figure Sa). One to 3 of these cells begin

134

av

PACIFIC SCIENCE, Volume 34, April 1980

FIGURE 4. Dorsal view of the posterior internal anatomy of L. pelodes showing the location of the gonad. a, anus;aI', anal vesicles; bl', blood vessel; cg, ciliated groove; g, gonad; i, intestine; ie, intestinal caecum; vnc, ventral nervecord. Scale equals I mm. Adapted by permission of the Smithsonian Institution Press from United States NationalMuseum Proceedings, Volume 96, "Echiuroid Worms of the North Pacific Ocean," by W. K. Fisher, April II, 1946,pages 215-292, Figure 12. Washington, D.C.: U.S. Government Printing Office, 1948.

to differentiate and are distinguishable bytheir increased diameter (Figure 5b). Theremainder do not differentiate but remainattached to the definitive oocytes. When anoocyte reaches a diameter of 40 11m itseparates from the cluster to continue differ-entiating as a single cell (Figure 5c). Uponattaining a diameter of about 100 11m theoocytes are selectively removed from thecoelomic fluid by the long coiled nephrosto-

mal lips (collecting threads). These threadslead to the nephridia (storage organs) whereoocytes are stored until spawning. Theoocytes are spawned in the germinal vesiclestage.

Gametogenic Cycle

The data presented in Figure 6 show theannual cycle of coelomic oocyte growth in

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Echiuran Reproduction off Southern California-PILGER 135

cFIGURE 5. Coelomic oocytes from L. pe/odes. a, a cluster of small primary oocytes recently released from the

gonad. Scale equals 10 Ilm. h, two differentiating oocytes still attached to the cluster of small cells. Scale equals 10Ilm. c, a coelomic oocyte that has dissociated from the cell cluster and is undergoing the remainder of oogenesis as asingle cell. Scale equals 20 Ilm.

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136 PACIFIC SCIENCE, Volume 34, April 1980

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E 20E .,- ,X " " 0.82 g), but lackedcoelomic gametes altogether, were sometimespresent in the samples but could not be sexed.The samples contained a greater percentageof individuals lacking coelomic gametes inwinter (26 percent) and spring (29 percent)than in summer (2 percent) and fall (11 per-cent). This indicates that in many individualsthe coelomic gamete population became de-pleted in winter and spring. This was pro-bably due to the accumulation of fullydifferentiated gametes in the storage organsprior to spawning (see Gamete Accumulationand Spawning below). By summer, the coelo-mic gamete population in most of the indi-viduals had been replenished with smallgametes released from the gonad. These datasuggest that the gonad of L. pelodes may haveundergone a period of quiescence which wasobscured by slight asynchrony in the popula-tion and the sampling bias described above.To test such a hypothesis would requireexamination of the gonad and careful repeti-

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Echiuran Reproduction off Southern California-PILGER 137

tive monitoring of the coelomic gametepopulation in single individuals over time.

Duration 01' OogenesisThe entry of oocytes into the coelomic

fluid during the summer defines periods ofoocyte growth which can be used to estimatethe duration of oogenesis (Figure 6). In May,June, and possibly July, 1975, small oocyteswere released into the coelom. The first ofthese became fully differentiated by October,indicating that the duration of oogenesis wasroughly 5 months (May to October). In asimilar manner, the oocytes that reachedmaximum diameter in October 1976 areassumed to have been released into thecoelomic fluid in April or May of that year.Thus, the term of oocyte growth was estimat-ed as having been 5-6 months. Estimatesfrom oocytes released at other times duringthe year are not practical since the growthof discrete size classes could not be followedwith certainty.

Oocytes that have reached maximum dia-meter are removed from the coelomic fluidand accumulated in the storage organs fromOctober through May.

Gamete Accumulation and Spawning

Annual fluctuations of the storage organvolume in specimens collected in differentyears from Santa Barbara, California, werepooled and are shown in Figure 7. The dataindicate that the storage organs are smalland empty in summer. The volume increasessharply in fall and continues through mid-winter as more and more gametes becomefully differentiated and are removed from thecoelomic fluid. The steady decline in storageorgan volume noted throughout the springis assumed to be the result of spawning. Bysummer the animals are spawned out and thestorage organs are empty again.

Juvenile Settlement

During late winter and early spring 1975,a large influx of very small juveniles «0.25 g)appeared in the population at White's Point

(Figure 8). These were assumed to be recentlysettled individuals. By April and May theyaccounted for as much as 75 percent of thepopulation (by numbers). With time theseindividuals grew and appeared in progressive-ly larger size classes or died. The number ofindividuals in the smallest size class remainedvery low from fall 1975 through early spring1976. Another influx of juveniles occurred inMay and June 1976. This settlement involvedfewer individuals than the one in 1975, wasrestricted to a narrower time-frame, and wasrecognizable as a distinct size class for ashorter time.

Growth to Sexual Maturity

The growth of newly settled juvenilesduring their first year can be predicted fromthe data presented in Figure 8. Since thepopulation size frequency distributions arenoticeably skewed by the influx of newlysettled juveniles, changes in the arithmeticmean weight for the entire population are apoor indication of growth during the firstyear. In this case, fluctuation of the mostfrequent size class (i.e., the mode) moreadequately represents the weight changes ofindividuals in these small size classes.

Growth of newly settled juveniles in thepopulation is seen graphically as a progres-sion of the modal size class toward heavierweight classes. The difference in weight of themodal class in the 12 months followingsettlement gives an indication of juvenilegrowth during the first year. In July 1975, themodal class was 0-0.25 g and comprisedindividuals which had settled in the precedingfew months. By January 1976, this class hadincreased to 0.75-1.0 g and was still quitedistinct. In June-July 1976, the mode for theindividuals which had settled in 1975 wasabout 1.50 g. Thus, in the 12 months follow-ing their settlement in 1975, the juvenileL. pelodes had attained a weight of approx-imately 1.5 g.

Based on the examination of several hun-dred individuals of various sizes, the smallestindividual in this study having differentiatinggametes in the coelomic fluid weighed 0.82 gand was assumed to have been about 6

138 PACIFIC SCIENCE, Volume 34, April 1980

801975 Jan.

n=44Feb.

n=50Mar.

n= 71Apr.

n=119

40

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FIGURE 8. Relative size frequency distributions of L. pelodes collected from January 1975 through September1976 at station 6C. The size classes are in 0.25 g increments of wet body weight.

months old. Thus, it is hypothesized thatL. pelodes juveniles from White's Point reachsexual maturity when they are 6 months to Iyear old.

DISCUSSION

Listriolobus pelodes was first describedfrom the stomach of flounders (Fisher 1946)

and at White's Point it is known to be themain food item of the dover sole, Microsto-mus pacificus (Lockington 1879; J. Allen,personal communciation). The bat ray,Myliobatis californicus, Gill 1865, is a sus-pected predator also since it is present withL. pelodes at White's Point and it is knownto eat other echiurans elsewhere (Fisher andMacGinitie 1928).

Listriolobus pelodes uses its proboscis

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Echiuran Reproduction off Southern California-PILGER 139

to feed on sediment deposits in a manner simi-lar to that described for Echiurus echiurus(Gish~n 1940), Ochaetostoma erythrogrammon(Chuang 1962), and Bonellia viridis (Jaccariniand Schembri 1977a, 1977b). Since L. pe/odesfeeds on sediment in some areas while leavingother areas undisturbed, it is hypothesizedthat the proboscis is able to discriminatequalitatively between different sedimenttypes. Jaccarini and Schembri (1977b) re-reported that Bonellia viridis has a feedingpreference for nutrient-rich fine sediments.The sensory structures that are involved inthis discrimination have not been described.Recent evidence indicates that this type ofselectivity is not restricted to adults sinceechiuran larvae show similar substrate pref-erences at the time of settlement (L. Suer,personal communication; see also Pilger1978).

Risk (1973) stated that the burrow ofListri%bus pe/odes is a gallery consisting ofas many as 4 openings to the surface. Thisstudy has shown, however, that the burrowsare U-shaped with exactly 2 openings to thesurface. U-shaped burrows with only 2 open-ings have also been described for the mud-dwelling echiurans Urechis caupo (Fisher andMacGinitie 1928) and Echiurus echiurus(Gislen 1940). Bonellia viridis, on the otherhand, lives in rock burrows having multipleopenings (Schembri and Jaccarini 1978), butthese dwellings are formed by the action ofUpogebia de/tura; B. viridis is only a second-ary resident that makes few, if any, modifica-tions to the burrow system (Schembri andJaccarini 1978).

The location of the gonad is known onlyin a couple ofechiuran species. Spengel (1879)described the gonad of Bonellia viridis,Rolando 1821, as being an area of differen-tiating peritoneal cells surrounding the post-erior part of the ventral blood vessel. Morespecifically, the gonad covers the blood vesselwhere it extends from the intestine to theventral nerve cord and a little farther anter-iorally. In Lissomyema me/lita (Conn 1886)the gonad surrounds a posterior muscle bandwhich "extends from the intestine to theventral nervous chord." Conn (1886) clearlydescribed the gonad as being in the same

location as in Listri%bus pe/odes but inter-preted the underlying structure as being mus-cular rather than vascular. The associationof L. pe/odes' gonad with the posterior ventralblood vessel corresponds well with what isknown in these 2 other echiuran species.However, the location of the gonad inechiurans which lack a vascular system(e.g., Urechis caupo) remains an enigma.

Scant information is available on thereproductive rhythms ofechiurans other thanL. pe/odes. From this study and the parenthe-tical remarks by others on 3 additionalechiurans, it is known that gamete produc-tion is seasonal in some species, and in atleast 1 other species it is continuous. Hiraiwaand Kawamura (1936) mentioned that eggproduction in Urechis unicinctus occurs dur-ing winter off Japan. The oogonia of Ikedo-soma gogoshimense first appear in the coelo-mic fluid in May and June and differentiationcontinues into winter (Sawada and Ochi1962). Urechis caupo off southern California,on the other hand, produces gametes con-tinuously (MacGinitie 1935) and contains alloocyte size classes in the coelom simultane-ously throughout the year (Gould 1967).

Miller and Epel (1973) attempted to deter-mine the time course of oogenesis in Urechiscaupo by radioactive labeling and subsequentmonitoring of coelomic oocytes. This ap-proach failed because it required that theanimals be retained in the laboratory for anextended period and Urechis caupo is not ableto maintain oogenesis during such a treat-ment. Das (1976) calculated the rate ofribosome production for different oocytestages and, considering the total amount ofribosomal material in a fully differentiatedU. caupo oocyte, predicted that oogenesiscontinues for 135 days. The value determinedfor Listri%bus pe/odes in this study (5-6months) is considerably longer; the methodsused in this study were also cruder than thoseused by Das. It is not possible to evaluatesuch differences without more specific infor-mation about the process of oogenesis inL. pe/odes.

Assuming continuous gamete productionin Urechis caupo, Gould-Somero (1975) rea-soned that the frequency of each oocyte size

140

class is proportional to the relative amount oftime an oocyte spends in that particular sizerange during oogenesis. Her data suggest thatthe rate of oocyte growth varies duringoogenesis. Specifically, the larger oocytesseem to grow faster than the smaller ones.Since gamete production by the gonad of L.pe/odes may not be a continuous event, thereasoning used by Gould-Somero (1975)cannot be applied here. It can be argued,however, that differential oocyte growth mayoccur in L. pe/odes, since a preponderance ofsmall oocytes was present in the coelomicfluid during several months of the studyperiod though there never was a month whenlarge ones prevailed.

The accumulation of ripe oocytes in thestorage organs of L. pe/odes takes place infall, winter, and part of spring. Spawning, onthe other hand, is limited to the springmonths. Thus, it is probable that at least thefirst batch of oocytes produced in the repro-ductive season remain in the nephridia for afew months before they are spawned. Themetabolic requirements of these oocytes maybe low since growth is negligible during thisphase. From November through Marchspecimens can be obtained routinely whichcontain large quantities of gametes in thestorage organs. This observation is in con-trast to the situation in the Sipuncula wheregametes are rarely found stored in thenephridia (Rice 1975).

Judging by the conditions of the storageorgans, Fisher (1946) noted that a specimenof L. pe/odes that was collected in June hadrecently spawned. His observation corre-sponds with the period defined by the presentstudy. The only other information on echi-urans available for comparison concernsUrechis caupo. This echiuran is reported toundergo partial or complete spawning in latesummer (Ricketts and Calvin 1962) despitethe fact that its gamete production is con-tinuous.

In studying the L. pelodes population atSanta Barbara, Barnard and Hartman (1959)stated that "mature individuals are thosemeasuring 25 mm or longer." According totheir data (Table 6, p. 13), these individualsshould weigh about 6 g. Personal observa-

PACIFIC SCIENCE, Volume 34, April 1980

tions ofechiurans from the same area (though13 years later) reveal that the lower weightlimit of sexual maturity is closer to 0.8 g.

Fisher (1946) noted that his smallestsexually mature specimen was just 7 mm long.Since individuals of that size usually arecontracted as small spheres (Pilger, personalobservation), the volume of his specimenprobably was about 0.2 ml and weighedabout 0.2 g (see Figure 2). Barnard andHartman's data support this conversion(1959: 13, Table 6). Fisher's observation isinconsistent with the findings of this studythat sexually mature individuals weigh atleast 0.8 g. A possible reason for this differ-ence is that Fisher's specimen probably wasone of the "small phase" individuals whichhad been loaned to him by Hartman (Fisher1946, pp. 238-239). If this is true, thencaution must be exercised in extending thereproductive information in the present studybeyond populations of normal-sized indivi-duals.

SUMMARY

I. LiSlriolobus pelodes lives in U-shapedburrows which it fashions in soft muddybottoms off southern California. Theproboscis is a highly extensible structureadapted for feeding on the uppermostlayer of sediment around each of theburrow apertures. Some degree of nutri-tional discrimination may take place. Theability of these echiurans to feed regularlyon large areas of the sediment surfaceimplies that the impact of their presenceon the trophic structure of the benthiccommunity is great.

2. The gonad of L. pelodes surrounds themost posterior portion of the ventralblood vessel. Early in oogenesis clustersof primary oocytes detach from the ovaryand differentiate in the coelomic fluid.When an oocyte reaches 40 /lm diameterit separates from the cell cluster andcompletes oogenesis as a single cell. Fullygrown oocytes are selectively removedfrom the coelomic fluid and accumulatedin the modified nephridia (storage organs)

•

Echiuran Reproduction off Southern California-PILGER 141

until spawning. The oocytes are spawnedin late prophase of the first meioticdivision but complete their maturationprior to syngamy.

3. Gametes are released by the gonad duringmost of the year but fully grown oocytesare present only in late fall, winter, andspring. The duration of oogenesis isestimated to be 5-6 months.

4. Spawning takes place over an extendedperiod from late winter through springand individuals are spawned out bysummer.

5. Juvenile recruitment occurs in late winterand spring. Newly settled juveniles becomesexually mature when they are 6 monthsto I year old.

ACKNOWLEDGMENTS

This work was part of a doctoral disserta-tion submitted to the Department of Biology,University of Southern California, LosAngeles. The advice, encouragement, andfriendship of Drs. Kristian Fauchald andRussel Zimmer have been invaluable through-out this study. The following people contri-buted in many ways: Dr. Robert Given,Richard Beckwitt, James Coyer, Jack Engle,Greg Hageman, Fred Piltz, and BruceThompson. I thank the Los Angeles CountySanitation Districts and their staff for pro-viding ship time, information, and theirlarge collection of L. pelodes. The supportof Dr. Mary E. Rice and the facilities of theSmithsonian Institution, Fort Pierce Bureau,are gratefully acknowledged. Ms. June Jonesskillfully typed the manuscript. My wife,Patty, contributed immeasurably and de-serves special thanks for her efforts.

LITERATURE CITED

BARNARD, J. L., and O. HARTMAN. 1959. Thesea bottom off Santa Barbara, California:biomass and community structure. Pacif.Nat. I: 1-16.

CHUANG, S. H. 1962. Sites of O2 uptake

in Ochetostoma erythrogrammon Leuckartand Ruepell (Echiuroidea). BioI. Bull.123: 86-93.

CONN, H. W. 1886. Life history of Thalas-sema. Studies BioI. Lab. (Johns HopkinsUniv.) 3:351-401.

DAS, N. K. 1976. Cytochemical and biochem-ical analysis of development of Urechiscaupo oocytes. Amer. Zool. 16: 345-362.

FAUCHALD, K. 1971. The benthic fauna inthe Santa Barbara Channel following theJanuary, 1969 oil spill. Page 426 in BioI.and Oceanographical Survey of the SantaBarbara Channel Oil Spill 1969-1970,vol. 1, BioI. and Bact. Allan HancockFoundation, University of Southern Cali-fornia, Los Angeles.

FAUCHALD, K., and G. F. JONES. 1976.Benthic macrofauna. In Final report onthe southern California baseline studiesand analysis (FY 1975-1976). Preparedby Science Applications, Inc., La Jolla,Calif., for the Bureau ofLand Management(U.S. Department of the Interior).

FISHER, W. K. 1946. Echiuroid worms of thenorth Pacific Ocean. Proc. U.S. Nat. Mus.96: 215-292.

FISHER, W. K., and G. E. MACGINITIE. 1928.The natural history of an echiuroid worm.Ann. Mag. Nat. Hist. 10:204-213.

GIBBS, P. E. 1976. Notes on the reproductivecycles of several Golfingia species (Sipun-cula). J. Mar. BioI. Ass. U.K. 56: 909-915.

GISLEN, T. 1940. Investigations on the ecologyof Echiurus. Lunds Univ's. Arsskr. n. ser.36. 10: 1-36.

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