A New Species Of Raricirrus (Polychaeta, Ctenodrilidae) From Wood Collected In The Tongue Of The Ocean, Virgin-Islands

11 Pages·1995·5.4 MB·

by  H K Dean

PROCEEDINGSOFTHE BIOLOGICALSOCIETY OFWASHINGTON
108(2):169-179. 1995.
A new species of Raricirrus (Polychaeta: Ctenodrilidae) from
wood collected in the Tongue of the Ocean, Virgin Islands
Harlan K. Dean
Department ofInvertebrates, Museum ofComparative Zoology, 26 Oxford St.,
Cambridge, Massachusetts 02138, U.S.A. and John Hazen White School ofArts and Sciences,
Johnson and Wales University, 6 Abbott Park Place, Providence, Rhode Island 02903, U.S.A.
Abstract.—Raricirrus variabilis new species (Polychaeta: Ctenodrilidae) is
described from the Tongue ofthe Ocean, St. Croix, Virgin Islands. This deep-
sea species was collected from submerged wood at 4000 m and is an apparent
organic-enrichment opportunist. Taxonomic differences between the genera
RaricirrusandRaphidrilusare discussed. The lifehistorycharacteristics ofthis
species are examined.
Woody plant material is rapidly broken 873), recovered 6 Dec 1980 (Alvin Dive
down in the deep sea by bivalves belonging 1079). Paratypes(MCZ4009) 12 specimens
to the family Pholadidae (Mollusca), sub- from samepanel anddates. Paratype (MCZ
family Xylophagainae. The activities of 401 1) one specimen from wood panel P-2;
these pholads have been shown to provide submerged 17 Dec 1978 (Alvin Dive 873),
a highly concentrated, tractable source of recovered 13 Dec 1980 (Alvin Dive 1082).
organicmaterialthatsupportsacommunity Paratypes (MCZ 4010) 6 specimens from
ofassociatedorganisms(Turner 1973, 1977, wood panel P-12; submerged 17 Dec 1978
1981). Manyoftheseassociatedspeciessur- (Alvin Dive 873), recovered 13 Dec 1980
vive in the deep sea by specifically finding (Alvin Dive 1082). Paratypes (USNM
and exploiting organically enriched sites 170552) 8 specimens from wood panel P-5
(Grassle & Morse-Porteous 1987, Smith & & P-13 wash material; submerged 17 Dec
Hessler 1987, Desbruyeres&Laubier 1988). 1978(AlvinDive873),recovered6Dec 1980
As part ofa long-term study ofsuch wood- (Alvin Dive 1079). Paratypes (USNM
associated communities by Dr. Ruth Tur- 170553) 4 epitokous specimens from 6 Ft.
ner, specimens of an undescribed poly- plank, wild wood; recovered 20 Dec 1978
chaete belonging to the family Ctenodrili- (Alvin Dive 876).
dae were recovered from pholad-riddled Description.—Benthic form: Body elon-
woodpanels and straywood ("wild wood") gatewithwidenedposteriorregion; anterior
retrieved from the deep-sea floor in the andmiddlebodysegmentslongerthanwide,
Tongue ofthe Ocean. This paper describes posterior segments much wider than long
mm mm
Raricirrus variabilis, new species, and fur- (Fig. 1). Holotype 6.75 long, 0.43
ther elucidates the separation oftwo cten- maximum width (modified segments) with
odrilid genera Raricirris and Raphidrilus. 27 setigers (Table 1, specimen S); paratypes
mm mm
1.54-7.59 long, 0.25-0.61 wide,
Raricirrus variabilis, new species with 18-31 setigers (Table 1). Prostomium
Material examined.—St. Croix, Virgin conical, eyespots lacking; nuchal organs
Islands: 17°56.63'N, 64°48.6'W, 4000 m. dorsolateral, appearing as slits or round de-
Holotype (MCZ 4008) from wood panel pressions with what appearto be cilia with-
P-13; submerged 17 Dec 1978 (Alvin Dive in. Prostomium with lateral oral folds; pro-
170 PROCEEDINGSOFTHE BIOLOGICALSOCIETYOFWASHINGTON
stomium,peristomiumandfirstsetigercon-
tinuous dorsally, differentiated ventrally.
Body of larger specimens brownish gray,
prostomiumbrownposterodorsally,firsttwo
setigers and posterior body region gold
brown across dorsum; smaller specimens
uniformly pale tan to cream color.
Branchial filaments greatly elongate (ap-
proximately 60% oftotal body length) with
club-like ends (Fig. 2), emerging postero-
dorsal to notopodia. Branchial filaments
fragileandeasilylostorbroken(incomplete
branchiaeonsetigers5, 7and8inholotype),
branchial scars on other segments not dis-
cernible; anteriormost occurrence observed
at setiger 2, posteriormost on last setiger
anteriorto the modified segments ofan ep-
itokous individual. Heart body a reddish
brown convoluted tube (Fig. 1) extending
for a variable (range shown in parentheses)
number of segments (4-11) beginning on
setiger 4 (4-6).
Notosetae and neurosetae emerging di-
rectly from body wall, lateral in anterior
region, becoming ventrolateral elsewhere.
Notosetae ofthree kinds: four to six capil-
laries finely serrate distally, usually one (1-
3)muchlonger(ca. %bodywidth)thanoth-
ers; shortpectinatesetaewithnarrow,wide-
ly spaced teeth (Fig. 3A) beginning in an-
terior half of body, grading into coarsely
pectinate falcigers in the midbody region
(Fig. 3B),andcoarselyserratesetae(Fig. 3C)
posterior to the modified setigers. Neuro-
setae three to six pectinate falcigers (Fig.
3D) increasing in length posteriorly; 1-2
straight, coarsely serrate setae (similar to
those ofposteriornotopodia) in the setigers
posterior to the modified setigers (Fig. 4).
Figs. 1-2. Raricirrusvariabilis,newspecies. 1.Dor- A pair of modified segments present as
salviewofholotype(specimen S). B = branchiae, HB first two segments of broadened posterior
= heart body, MS ^ modified segments, N = nuchal mm
organ,O=oocytes,OF=oralfold,S=enlargedspine, regioninallbutseveral smaller(<2.73
ST = reproductive stylet, SV = seminal vesicle. Scale long) individuals (Table 1). Modified seg-
bar = 1.0 mm. 2. Distal end ofbranchia (specimen ments distinct dorsally (Fig. 6), with one
MCZ4011). Scale bar = 100 ^m. pair of large, curved notopodial spines
emerginganterolaterally from second mod-
ified segment (holotype with only a single
spineonrightside),fittingintodeepgrooves
onposteriorventralsurfaceoffirstmodified
VOLUME 108, NUMBER 2 171
AB
CD
Fig. 3. SetaeofRaricirms variabilis, newspecies. A-C. Notosetae: A. Shortpectinatefalcigerwiththebases
ofseveralcapillary setae from anteriorregion. B. Coarselypectinatefalcigerfrom midbodyregion. C. Coarsely
serratefalcigerfromregionposteriortothemodifiedsegments.D. Pectinateneuropodialfalcigersfrommidbody
region. Scale bars = 10 ixm.
172 PROCEEDINGSOFTHEBIOLOGICALSOCIETYOFWASHINGTON
Figs. 4-7. Raricirrus variabilis, new species. 4. Coarsely serrate neuropodial falciger from region posterior
tothemodifiedsegments. Scalebar= 50tim. 5. Posteriorregionofepitokousindividual(specimenW), ventral
view.GP=genitalpore,SO=sphericalorgan.Scalebar=500/um.6.Modifiedsegmentsofepitokousindividual
(specimen W), dorsal view. Scale bar = 500 /u.m. 7. Reproductive stylet(specimen R). Scalebar = 50nva.
segment (Fig. 5). Three specimens (includ- (Fig. 5, SO). Spherical structure appeared
ingholotype)withapairofenlarged, straight empty or sometimes contained diffuse,
spines in notopodia of 1-2 setigers anterior coarse-grained material when examined in
to modified segments. Median pore ob- squash preparation. Pygidium roundedwith
served on ventral surface ofsecond modi- dorsoterminal anus.
fied segment (Fig. 5, GP), associated with a Oocytes observedscatteredin severalan-
medial spherical area within first modified terior setigers ofseveral benthic specimens
segment or segment immediately anterior (numerous 10-25 Mm diameter oocytes in
VOLUME 108, NUMBER 2 [73
setigers5-9ofholotype);thesesetigersoften 18-22 in largerindividuals. The number of
thin-walled and delicate. Straight cuticular setigers posterior to the modified segments
stylet (Fig. 7) with narrow lumen present (character 6) was variable (2-9 in benthic
from five to nine setigers (five in holotype) forms, 9-11 in epitokes), but generally
anterior to modified segments in several ranged from five to seven in larger benthic
specimens, associatedwithalarge sac(sem- individuals.
inal vesicle) of what were revealed to be Thevariabilityinthedistributionofsetal
spermatozoain squash preparation (Fig. 1). types displayed in the benthic form ofRar-
Presenceanddevelopment ofmodified seg- icirrus variabilis made the characterization
ments apparently unrelated to presence of ofbody regions based on setal characteris-
either observable oocytes or a stylet and ticsimpossible. Thegreatestnumberofcap-
seminal vesicle. illarynotosetae(character7)occurredinthe
mm
Epitokes. —Specimens 6.67-20.64 firstorsecondsetigerwithfromfourto sev-
mm
long, 0.73-2.07 wide, 28-35 setigers en capillaries per setal bundle, from one to
(Table 1). Midbody region brown-gray, three ofthese capillaries much longer than
clearly differentiated from light cream col- the rest. Subsequent notopodia possessed
ored and much narrower posterior setigers. from one to five capillaries with a single
Capillary setae more numerous in notopo- elongate capillary per setal bundle. The an-
dialbundles(5-16)andwithagreaternum- teriormost occurrence ofnotopodial pecti-
ber(2-9) ofelongate capillaries (ca. % body nate falcigers (character 1 1) was usually at
width) than in benthic specimens. Noto- setigers 3-9, althoughthe firstoccurrenceof
podial falcigers lacking; straight, coarsely such setae was at setigers 10-13 in several
serrate setae present posterior to the mod- specimens. Coarsely serrate notosetae
ified segments. Neurosetae similar to those (character 12) were usually present begin-
of benthic individuals but with a greater ningimmediately posteriorto the modified
number of falcigers (maximum of 8-10). segments and were absent in most of the
mm
Heart body extending through five to eight smaller individuals (<3.20 long) ana-
setigers starting at setigers 8-10. The body lyzed. Several specimens possessed serrate
cavity of two epitokous specimens (Table notosetae in the last setiger anterior to the
U
specimens andX)containednumerous modified segments.
1,
oocytes from setigers 6-8 to the first seg- Similarcoarsely serrate neurosetae (char-
ment anterior to the modified segments. acter 15) were present in all but three ofthe
Maximum diameter of these oocytes was smaller individuals and were commonly
approximately 140iimandeachoocytecon- found only in the posterior setigers. Several
tained a round germinal vesicle in the nu- specimens had coarsely serrate neurosetae
cleus, and was filled with coarse, yolky ma- in from one to five setigers anterior to the
terial. modifiedsegments. Enlarged, curved spines
Other material.—While trends in mor- ofthemodifiedsegments(character 16)usu-
phological characters are apparent. Table 1 ally occurred either as a single or double
illustrates thegreat morphological variabil- pair. Several ofthe specimens with well de-
ity expressed by this species. The anteri- veloped modified segments either lacked
ormost occurrence ofthe heart body (char- enlarged spines or possessed only a single
acter 4) in benthic forms was in setiger 4, spine.
usuallyextendingthrough 9 segmentsto se- Three of the four epitokous individuals
tiger 12(from4-6to7-14);inepitokesfrom examined were much largerthan any ofthe
8-10 to 13-16. Modified segments (char- other specimens and possessed a greater
acter 5) were absent in some smaller spec- number ofsetigers than any ofthe benthic
imens and present in the region ofsetigers individuals examined (Table 1). The heart
'
174 PROCEEDINGS OFTHEBIOLOGICALSOCIETYOFWASHINGTON
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VOLUME NUMBER
108, 2 175
body of the epitokous specimens did not (14-20 mm) than thebenthic form with the
occuruntilsetiger8-10, extendingtosetiger elongatecapillarysetaeonly75%ofthebody
13-16. Modifiedsetigerswerepresentatthe width.
sameorslightlymoreposteriorsetigersthan Etymology.—The specific name refers to
in the benthic form, but the number ofse- the variability in the distribution of setal
tigersposteriortothese segmentswasgreat- types.
er in the epitokous specimens (9-12).
Discussion
Epitokousindividualspossessedagreater
number ofcapillary notosetae along with a The family Ctenodrilidae is now com-
greaternumberofelongatecapillariesinthe prised ofthe subfamilies Ctenodrilinae and
anterior and midbody setigers. Notopodial Raphidrilinae,eachwithtwodescribedgen-
pectinate falcigers were absent in the epi- era.ThegeneraCtenodrilusClaparede, 1863,
tokous specimens while serrate notosetae andAphropharynxWilfert, 1974,areunited
were present only in the segments posterior within the subfamily Ctenodrilinae bytheir
to the modified segments. Coarsely serrate lack of branchial filaments while the sub-
neurosetae were found only posteriorto the family Raphidrilinae consists ofthe genera
modifiedsegmentswiththeexceptionofone Raphidrilus Monticelli, 1910, and Raricir-
epitokous individual with such neurosetae rus Hartman, 1961, both possessing bran-
presentinthesegmentimmediatelyanterior chiae. Morphological differences between
to the modified segments. Raricirrus and Raphidrilus are slight, how-
Remarks. —Raricirrus variabilis differs ever, and there has been some doubt as to
from R. maculatus Hartman, 1961, and R. whethertheirseparationisjustified(seedis-
beryli Petersen & George, 1991, in the pos- cussion in Petersen & George 1991).
session ofa more anteriorly situated heart Based on the descriptions ofRaphidrilus
body, the presence ofpectinate notopodial nemasoma, an analysis ofthe type material
falcigers in the benthic stage, the presence ofRaricirrus maculatus and the analysis of
ofa seminalvesicleandreproductive stylet, specimens ofRaricirrus beryli, Petersen &
and the apparent absence ofan asexual re- George (1991) retained separation of Ra-
productive mode. Raricirrus variabilis and phidrilus and Raricirrus and identified sev-
R. maculatus share the presence ofa mod- eral morphological characters that could be
ified region with large curved spines in at useful in differentiating these two genera.
least some specimens, although that ofR. These characters include the position and
maculatus is a apparently single modified extentoftheheartbody, the structureofthe
segment while that ofR. variabilis is com- nuchal organs, the structure ofthe head re-
posed oftwo segments incompletely sepa- gion,andthepresenceofaregionwithmod-
rated dorsally. Raricirrus variabilis differs ified setae.
from R. beryli in lacking the ciliated region Petersen & George (1991) had used the
anterior to the mouth opening and on the anteriormost occurrence ofthe heart body
ventral surface ofthe first two setigers. as a distinguishing character for the genera
Epitokous individuals of R. maculatus Raphidrilus and Raricirrus. That ofRaphi-
have not been encountered while a single drilus nemasoma has been reported to first
immaturemaleepitokeofR. berylihasbeen appear at setiger 4 while that of the two
described (Petersen & George 1991). The previouslyknownspeciesofRaricirrusdoes
epitoke of R. beryli was smaller (11 mm) notoccuranteriorto setiger8 or9 (Peterson
than the benthic form, with elongate cap- & George 1991). Unfortunately this gener-
illarysetaeapproximately 150%ofthebody alization does not hold true forR. variabilis
width. The epitokous individuals ofR. var- as the heart body begins at setiger 4 (4-6)
iabilis are (with one exception) much larger in the benthic specimens taken from the
176 PROCEEDINGSOFTHE BIOLOGICALSOCIETYOFWASHINGTON
wood panels and does not appear until se- (Schlotzer-Schrehardt 1987, 1991). This
tigers8-10intheepitokousindividualsfrom variability in the morphology ofnuchal or-
the wild wood. The heart body of poly- gans within a species as well as a lack of
chaetes has been viewed as being of he- knowledge regarding nuchal organ variabil-
matopoietic function (Kennedy & Dales ity within a family orgenus precludes their
1958) however, more recent work has in- use (at the light microscope level) in differ-
dicated that this organ could also have a entiating between these two genera.
protective function. Vovelle et al. (1995) Petersen&George(1991)alsoreferredto
notedchemicaldifferencesintheheartbod- the shape and arrangement ofthe head as
ies of specimens of Raricirrus beryli col- perhaps beingofpossible taxonomic signif-
lectedadjacentto andaway from the North icance. Theprostomium, peristomium,and
Sea oil platforms indicating a possible role first setiger ofRaricirrus beryli and R. ma-
inthedetoxificationofhydrocarbonsinthis culatusare described by Petersen & George
polluted environment. While the anterior- (1991)asformingasingle"visualunit"with
most occurrence ofthe heartbody seems to all these segments united along the dorsal
be a valid specific character and may pos- surface. In the figures ofMonticelli (1910)
sibly be related to the ability ofa species to and Sokolov (1911) the prostomium and
cope with its environment, it is not useful peristomium oiRaphidrilus nemasoma ap-
in the differentiation ofgenera. pear to be united dorsally while the first
Sokolov (1911) described the nuchal or- setigeroussegmentisclearlyseparatedfrom
gansofRaphidrilusasoften-closedslitswith these segments. The prostomium, peristo-
short cilia extending from the base of the miumandfirstsetigeroussegmentofR. var-
pit while Petersen & George (1991) de- iabilisarealsouniteddorsallyandthischar-
scribedthoseofRaricirrusasbareovalareas acter may be ofutility in the separation of
surrounded by fields ofcilia. The majority RaphidrilusandRaricirrus. Furtheranalysis
ofspecimens ofR. variabilisexaminedpos- of material belonging to the genus Raphi-
sessedslit-likenuchalorganswithnovisible driluswould be required to substantiate the
ciliation ofthe surroundingprostomial sur- use ofthis morphological character in sep-
face when viewed using scanning electron aration ofthe two genera.
microscopy. Several specimens that were Raricirrus variabilis is placed within the
observed under the dissecting microscope genus Raricirrus, rather than Raphidrilus,
had the rims oftheir nuchal organs widely primarilyduetoitssetalcharacteristics.Ra-
expanded, exposing what appeared to be a phidrilus nemasoma is described as pos-
uniformlyciliated surfacewithin. The mor- sessing only capillary notosetae and neu-
phologyofthenuchalorgansofR. variabilis rosetae with the exception ofseveral mod-
is more similar to that described for the ified segments possessing thick spines
genusRaphidrilusthanforRaricirrus. How- (Monticelli 1910, Sokolov 1911).Raricirrus
ever, while the ultrastructure ofnuchal or- variabilis, aswellastheothertwo described
gans has been utilized in the recognition of species in thisgenus, possesses both serrate
possible phylogenetic relationships among capillariesandcoarselyserratesetaeintheir
polychaetefamilies (Purschke 1986), the use notopodia.R. variabilisdiffersfromtheoth-
of their gross morphology as a taxonomic erspeciesinthepossession ofshort, coarse-
character at the generic level is question- ly serrate falcate spines (Fig. 3A) in the an-
able.Nuchalorgansmaybeeversible(Whit- teriornotopodiawhileR. maculatusandR.
tle & Zahid 1974) with associated retractor beryli both have long, natatory capillaries
muscles (Purschke 1986) and may vary in in their "dispersal" forms (Petersen &
morphology at reproductive maturity, per- George 1991). Thefinelypectinatefalcigers,
haps exhibiting sexual dimorphism grading to coarsely serrate forms posted-
VOLUME 108, NUMBER 2 177
orly, arecharacteristic ofallthree speciesin Sea oilfields (Moore 1991, Petersen &
the genus. George 1991).Raricirrisberylihasalsobeen
Based on the analysis ofRaricirrus var- collected by A. Norrevang in shallow (5 m)
iabilis, the generic diagnosis for Raricirrus waters in Skopun Harbor in the Faroes, a
Hartman, 1961 emended by Petersen & harbor without any apparent elevated hy-
George 1991,isfurtheremendedasfollows: drocarbon input (Petersen 1994 pers.
Raricirrus Hartrmin, 1961, emended. comm.). Based on strong association with
Type species. —Raricirrus maculatus high concentrations ofcertain components
Hartman, 1961, by monotypy and original of the aromatic fraction of hydrocarbons,
description. Moore (1991) hascharacterizedR. berylias
—
Z)/a^«05/5. Raphidrilinae with prosto- apolychaeteindicatorspeciesforsediments
mium not obviously delimited from peri- containing pollution levels of hydrocar-
stomium and setiger 1 dorsally; with or bons. The epitokes and/or larvae ofR. var-
without ventral cilia on peristomium and iabilis are most likely attracted to sites in
first few segments; last 6-9 setigers shorter the deep sea with high concentrations of
and wider than preceding ones, forming a organic material such as decaying wood.
distinct posteriorregion. Branchiae simple, The largest eggs observed in female epi-
filamentous, maybeclublikedistally. Heart tokes (Table 1, specimen U) ofRaricirrus
body in variable number of anterior and variabiliswereapproximately 140ixvaindi-
middle segments. Notosetae serrate capil- ameter. While any determination ofmode
lariesandcoarselyserrateformsposteriorly, ofdevelopmentbasedonegg size shouldbe
some species also with short pectinate fal- done with great caution (Bridges 1993), it
cigers; neurosetae falcate and finely pecti- isprobablethatthisspecieshaseitherdirect
nate anteriorly, grading to coarsely serrate developmentorashortlecithotrophiclarval
forms posteriorly; simple curved spines mode ofdevelopment. Assumingthatthese
sometimes replacing most orall normal se- eggs approximate egg size at maturity, their
tae in 1 or 2 modified posterior segments diameter compares favorably with those of
of some species. With or without seminal the unknown species of Raphidrilus {Ra-
vesicle and reproductive stylet. phidrilus nemasoma (sic)) studied by Qian
Remarks.—Raricirrus variabilis is an ex- & Chia (1989). By following the develop-
ample of an opportunist in the deep sea ment ofnewly fertilized eggs, Qian & Chia
whichsurvivesbyfindingandexploitingor- found that the eggs ofRaphidrilus sp. de-
ganically enriched sites (Grassle & Morse- veloped directly into free-crawling pre-
Porteous 1987). The two previously de- adults. Similarly the eggs of R. variabilis
scribedspeciesinthegenusarealsoreported may produce preadults through direct de-
from environments with elevated levels of velopmentsubsequenttodeep-seadispersal
organic carbon being most positively cor- bytheepitokousbodyform. Bridges(1993),
related with elevated levels of hydrocar- for example, has reported a lecithotrophic
bons. Raricirrus maculatus is known from mode ofdevelopment for a morph ofStre-
an area close to an industrial waste dis- blospio benedicti with eggs 100-200 ixm in
charge site in fine sediments that are con- diameterand itis also quite possible, based
taminated with heavy metals and chlori- upon egg diameter, that R. variabilis may
natedhydrocarbons (Hartman 1961, Peter- also have a lecithotrophic mode of devel-
sen & George 1991). Raricirris beryli was opment rather than direct development.
firstreportedatlowdensitiesfrom a sewage Additionally, dispersal may also be accom-
sludge dumping ground and at very high plished by some type of asexual dispersal
densitiesin fine sedimentswith high hydro- form similar to that reported for R. beryli
&
carbonconcentrationsfromnorthernNorth by Petersen George (1991).
78 PROCEEDINGSOFTHE BIOLOGICALSOCIETY OFWASHINGTON
Two body forms were recognizedinRar- productive stage for R. variabilis (although
icirrus variabilis, a "normal" benthic form thepossibilityexiststhattemporallyrestric-
and a form similar to what Petersen & tive sampling could have missed such an
George (1991) identified as an epitokous asexual stage if it were a seasonal event).
phase for R. beryli. They considered this This species seems to have adapted a dif-
bodyform asan epitoke because itwas sex- ferent reproductive strategy in the exploi-
ually mature with the body usually packed tation of its patchily distributed resource.
withgametes. TheepitokousformofR. var- Many specimens ofthe benthic form ofR.
iabiliswaslooselyorganizedwithmuchfree variabilis contained both developing eggs
movementofthenumerouslargeeggswith- and sperm and were evidently hermaph-
in the interioroftheworms. This mayhave roditic. Hermaphroditism has often been
been an artifact ofpoor fixation or may be associated with patchy, unpredictable en-
indicative ofthe transient nature ofthis life vironments (Petraitis 1991) and may allow
stage with the individuals reduced to little R. variablis to enhance its exploitation of
morethaneggcontainers. TheepitokeofR. widelyscatteredpatchesoforganic material
variabilis differs from the one immature on the deep-sea floor. The benthic form
male epitoke ofR. beryli described by Pe- could function as both genders or as the
tersen&George(1991)inthatitscapillaries genderwhichwouldmaximizereproductive
are only 0.75 times the body width while success under existing environmental con-
thoseofR. beryliwereabout 1.5 timesbody ditions similar to the strategy proposed for
width. Capitella capitala by Petraitis (1991).
Petersen & George (1991) also described Once established on a patch of suitable
athirdbody form theyreferredto asa "dis- organicresource,thebenthicformofR. var-
persal"formwhichhadcapillaries2-4times iabilis may engage in sexual reproduction,
the body width but with no obvious ga- maximizingitsreproductivesuccessthrough
metes. Petersen & George (1991) hypothe- its hermaphrodism. The resultant free-liv-
sized that this dispersal form may disperse, inglarvaewouldincreasethepopulationsize
settle and then develop into spawning epi- at the home site although at a reduced rate
tokes. There were no specimens ofi?. var- when compared to the exploitation of a
iabilis recovered, from the wood panels or comparable resource in shallower waters.
the piece ofwildwood, thatwere analogous Some ofthe benthic individuals could de-
tothedispersalphaserecognizedforR. ber- velop into the epitokous form, either as a
yli. routinepercentageofthepopulationasseen
Manyspecimensofthetwoshallow-water inDedocaceria caulleryiOersted(Gibson &
species, R. beryli and R. maculata, exam- Clark 1976) or perhaps in response to de-
inedbyPetersen&George(1991)displayed teriorating resource, as a means ofcoloniz-
evidenceofregenerationsubsequenttofrag- ing suitable habitat elsewhere.
mentation. Both of these species seem to
rely on asexual reproduction as a means of
Acknowledgments
exploiting their high organic, high hydro-
carbon content, environment. Following Thesepolychaeteswerecollectedanddis-
colonization ofa patch of suitable habitat sected from wood panels as part of R. D.
by some type ofdispersal form, asexual re- Turner's studies of deep-sea wood-boring
productionwould providea means ofrapid communities,aprojectsupportedbytheOf-
population growth in order to better utilize fice of Naval Research, Contract no.
the available resource (Schroeder & Her- NOOO14-84-0258 withHarvardUniversity.
mans 1975). The SEM pictures were taken with an ABT
There was no evidence ofan asexual re- 55 SEM generously provided by R. Prezant