Gastropod Egg Capsules and Their Contents From Deep-Sea Hydrothermal Vent Environments

22 Pages·1991·9.2 MB·English

by  R G Gustafson

Reference: Bio/. Bull. 180: 34-55. (February. 1991)
Gastropod Egg Capsules and Their Contents From
Vent Environments
Deep-Sea Hydrothermal
R. G. GUSTAFSON, D. T. J. LITTLEWOOD, AND R. A. LUTZ
Institute ofMarine and Coastal Sciences, Rutgers University, New Brunswick, NewJersey 08903
Abstract. Eggcapsules from three different prosobranch Introduction
gastropods were retrieved from the Galapagos Rift and Active hydrothermal vent systems accompanied by
Juan de Fuca Ridge deep-sea hydrothermal vent fields. dense benthic fauna occurat several widely separated sites
The morphology ofthese capsulesand theirexcapsulated along active oceanic ridges in the eastern Pacific, from
embryos and larvae are described and illustrated. Based 48N along the Juan de Fuca Ridge, to 22S along the
on their capsule type and the protoconch morphology of East Pacific Rise. Known hydrothermal fieldson theJuan
their contained larvae, 29 lenticular capsules from the de Fuca Ridge are separated by as much as 100 km,
Galapagos Rift could be attributed to a provisionally de- whereasseparation alongtransform faultson the East Pa-
scribed neogastropod turrid, Phymorhynchus sp. But 3 cific Rise indicates that vent fields are at least 100 km
inflated, triangularcapsules from theGalapagos Rift,and apart in this region (Crane, 1985; Grassle, 1986). Local
56 different egg capsules from the Juan de Fuca Ridge, vent habitats appear to be transient, with populations
each shaped like an inflated pouch, could not be unam- being susceptible to intermittent establishment and ex-
biguously assigned to a member ofthe known vent gas- tinction (Lulzeial., 1985;J. F. Grassle. 1985; Lutz, 1988).
tropod fauna. The mode of development and potential Despitetheirapparentgeographic isolationand ephemeral
fordispersal isinferredfrom eggcapsuletype, thenumber nature, vent areas are characterized by the remarkable
ofembryos percapsule, and protoconch characters com- similarity oftheir faunal assemblages (Lutz, 1988). Fun-
parable to those ofconfamilial shallow-water gastropods damental biological questions remain regarding both the
mannerin which these ephemeral habitatsarecolonized,
forwhichthetypeofdevelopment isknown. Thesecriteria
and acomparison tothe knownjuvenileshell morphology and the mechanisms of organism dispersal and rates of
gene flow between discrete areasofhydrothermal activity
ofPhymorhynchus sp., suggest that, after encapsulation, associated with contiguous and non-contiguous oceanic
this speciesdevelops planktotrophically and iscapable of
ridge systems.
long-range dispersal. Similar evidence suggests that the Becauselaboratorycultureofdeep-seaorganismsisdif-
larvae contained in the inflated triangular capsules from ficult (Turneret ui, 1985), many ofourperceptionsabout
the Galapagos Rift may also develop planktotrophically the development and larval dispersal ofvent biota have
afterhatching;butthelarvaeinthepouch-likeeggcapsules been, by necessity, inferred from analyses ofegg size, fe-
from the Juan de Fuca Ridge probably develop non- cundity, and morphology oflarval structures retained on
planktotrophically without a dispersal stage. These de- juvenile and adult specimens. Gastropod mollusks have
velopmental patterns are characteristic ofshallow-water been widely used forsuch studies, becausea record ofthe
members ofthe systematic groups to which these species larval developmental pattern can be inferred from the
belong, indicating, as previous studies have shown, that morphologyofthe initial shell, comprisingtheProtoconch
vent gastropods can persist in these patchy, ephemeral I in non-planktotrophic speciesand, also, the Protoconch
environments in the absence of unique adaptations al- II shell stages, in planktotrophic species (Powell, 1942;
lowing dispersal between active hydrothermal sites. Thorson, 1950;Shuto, 1974; Robertson, 1976: Jablonski
and Lutz, 1980).
The mode oflarval development in recent (Rodriguez
Received 14 August 1990; accepted 30 November 1990. Babio and Thiriot-Quievreux, 1974; Bandel, 1975a, b, c,
34
HYDROTHERMAL VENT EGG CAPSULES
1982; Bouchet, 1976a, b; Scheltema. 1978; Bouchet and (Vol) provides an index to the developmental type ofa
Waren, 1979b; Rex and Waren. 1982; Scheltema and marine prosobranch gastropod. A specieswith morethan
Williams. 1983; Lutz ctal., 1984, 1986;Turnerand Lutz, three whorls and a D/Vol value less than 0.3 suggests
1984; Turnerctal.. 1985;Colman ctal., 1986; Lutz, 1988; planktotrophicdevelopment. A D/Vol valuebetween 0.3
Lima and Lutz, 1990) and fossil (Jung, 1975; Scheltema, and 1.0 with less than three volutions indicates a species
1978, 1981; Jablonski and Lutz, 1980, 1983; Bouchet, with either planktotrophic or non-planktotrophic devel-
1981;Hansen. 1982, 1983;Jablonski, 1986)prosobranch opment, whereas a D/Vol value between 0.3 and 1.0 and
gastropods has been classified as either planktotrophic or less than 2.25 volutions suggests a species with a non-
non-planktotrophic based on criteria oflarval shell mor- planktotrophic larvaltype. AD/Vol valuehigherthan 1.0
phology formulated by Kesteven (1912). Dall (1924), would suggest a species with direct development (Shuto,
Powell (1942), Thorson (1950), Robertson ( 1971, 1976), 1974). However, Pawlik ct al. (1988) have shown thatthe
Rodriguez Babio and Thiriot-Quievreux (1974), Shuto criteria ofShuto ( 1974) cannot accurately predict the ac-
(1974), Sohl (1977), and Jablonski and Lutz (1980, 1983). tual mode ofdevelopment in a majority of cancellariid
Prosobranch species with larval shells having 1.5 to 9 gastropods.
whorls, a distinct fine sculpture, a brown coloration in The type ofsculpture or ornamentation on the proto-
contrast toawhiteorgrayadult shell, anarrowhigh spire, conch has been widely used to infer the mode ofdevel-
a clear difference between the Protoconch I and Proto- opment in prosobranch gastropods (Thorson, 1950;
conch II, and possibly a projection on the outer lipofthe Shuto, 1974; Bandel, 1975a, b, c, 1982; Lima and Lutz,
larval shell which interdigitates with the velum [("sinu- 1990). Planktotrophy has been indicated forthose larvae
sigera" larvae in terminology of Robertson (1976)] are with protoconchs possessingafine reticulateorcancellate
categorized as planktotrophic. Species with larval shells pattern, oblique radial ribs or both, whereas a smooth or
having 0.5 to 1.5 whorls, simple or no ornamentation, simply sculptured protoconch suggests that the larvaeare
the same coloration as the teleoconch, a large bulbous non-planktotrophic (Thorson, 1950; Shuto. 1974; Bandel.
apex, and no evidence ofseparation between the Proto- 1975a, b, c, 1982). A well developed protoconch orna-
conch I and Protoconch II are categorized as non-plank- mentation is thought to strengthen the shell, a benefit to
totrophic. In thegeneral terminologyofThorson's (1950) planktotrophic larvae spending lengthy periods in the
"apextheory."shellsoftheplanktotrophictypearetermed plankton (Bandel, 1975a; Jablonski and Lutz, 1980). Two
multispiral or polygyrate and shells ofthe non-plankto- recent reviews of poecilogony, or intraspecific variation
trophic type are termed paucispiral. in the mode of larval development, found no evidence
Although these criteria allow differentiation between for the occurrence of this phenomenon in prosobranch
planktotrophic and non-planktotrophic larvae, recent gastropods, indicating that the form ofthe protoconch is
culturing oftrochoidean archeogastropods demonstrates a species-specific character (Hoagland and Robertson,
thatthepresenceofapaucispiral protoconch isinsufficient 1988; Bouchet, 1989). Nevertheless, the species variability
evidence on which to discriminate between a planktonic ofprotoconch and teleoconch morphologies ofcultured
and a non-planktonic larval existence (Hadfield and meso- and neogastropods led Lima and Lutz (1990) to
Strathmann, 1990). Offour trochoideans cultured, Had- stress the need for caution when inferring type ofdevel-
field and Strathmann (1990) found two with pelagic de- opment from shell morphology alone.
velopment of7 d or more and two with entirely benthic The most reliable method for determining develop-
life histories, although all four produced veliger larvae mental mode from protoconch morphologies is to com-
and had similar inflated paucispiral protoconchs. Al- pare confamilial or congeneric species with known de-
though the mode oflarval development in shelled opis- velopmental histories (Scheltema, 1978; Jablonski and
thobranchs may also be reflected in the larval shell mor- Lutz, 1980, 1983). In the case ofdeep-sea prosobranchs,
phology, this relationship has not been demonstrated thecomparison mustbemadewith taxonomicallyrelated
throughout the group (Rex and Waren, 1982). shallow-water species, the assumption being that similar
Ockelmann (1965) formulated criteria distinguishing protoconch morphologies result from similar life history
between planktotrophic and non-planktotrophic devel- patterns in shallow and deep seas (Colman et a/.. 1986).
opment in a wide range of bivalves based on relatively Based on the above larval shell criteria, the majority of
precise dimensions ofthe prodissoconch I and II, but the vent gastropods are believed to have non-planktotrophic
only effort to establish similar criteria forgastropod pro- development and to have limited larval dispersal capa-
toconchswas based on data from comparatively few spe- bility (Lutz et a/., 1984, 1986; Turner et al, 1985), al-
cies (Lima and Lutz, 1990). Nevertheless, Shuto (1974) though lowtemperaturesencountered in thedeepseamay
has shown that, given a complete Protoconch I and II, extend the period available fordispersal ofswimmingbut
the ratio of the maximum diameter (D; in mm) of the non-feeding veligers(Turneretal., 1985). Thisabundance
whole protoconch to the number ofwhorls or volutions ofnon-planktotrophy may, in part, beduetothe factthat
36 R. G. GUSTAFSON ET AL
Table I
DS\' "Alvin"Jivenumber, dale, location, latitude/longitude, anddepthojdive* in whichgastropodeggcapsules wereretrieved
Dive* Date Location Latitude; Longitude Depth (m)
1418
HVDROTHERMAL VENT EGG CAPSULES
table II
.IvcniKcdimensions(mean standarddeviation) i>lhydrothermal vei
gastropodeggcapsulescollectedon specificdives o/AST ".ilvin"
Numberojspecimenscollectedoneach diveareinparentheses
Galapagos Rift LenlicularEggCapsules
38 R. G. GUSTAFSON ET AL
Early trochophore and veliger larvae in various stages
' ofdevelopment were present in capsules collected during
"Alvin" Dives 1528, 1529, and 1531 (Figs. 6-11): one
capsulecollectedduring Dive2031 contained 1052 veliger
larvae, all with a fully formed Protoconch I (Figs. 12-14).
All other lenticular capsules collected during Dive 2031
were empty. No nurse eggs were observed in lenticular
egg capsules.
The following is a chronological reconstruction ofde-
velopmental stages found in a number oflenticular cap-
sules from theGalapagos Rift. The earliest stage encoun-
tered, a late prototroch, was approximately 175 ^m in
length by 100 /um in width (as measured from electron
micrographs), with a prominent apical plate, short pre-
trochal region, prototroch. long post-trochal region,
mouth, andveryearly larval shell (Figs. 6-10). Theapical
plate lacked an apical ciliary tuft while the prototrochal
cilia appeared to be ofthecompound type and 15-19 //m
in length (Fig. 7). The posterior-dorsal shell field(see Eys-
terand Morse, 1984, forterminology) had already invag-
inated in the earliest specimens obtained, and some shell
secretion had commenced (Figs. 8-10).
The next observed stage ofdevelopment was a veliger
larva, which had a bi-lobed velum, a mouth leading into
the stomadeum, a foot primordium a protruding knob
located immediately posterior to the mouth an oper-
culum. and a more developed larval shell (Fig. 1 1). This
was a very early veliger because the body was still much
too large to be withdrawn into the shell.
One capsule collected during Dive 2031 (Figs. 12-14)
contained late Protoconch I larvaethatwerealmost ready
to hatch. The embryonic shells ofthese specimens had a
maximum diameterof234^m(asmeasuredfromelectron
micrographs). The larval shells ofthese larvae had a fine
reticulate sculpture formed ofspiral raised ridgesrunning
in thedirection ofgrowth, and crossed by regularlyspaced
perpendicular riblets (Figs. 12-14). An uncalcified oper-
culum was present at this stage (Fig. 13).
Galapagos Rift inflated triangular egg capsules
mm
Three specimens of an egg capsule 4.1 0.9 in
mm mm
length by 1.3 0.3 in width by 3.0 0.5 in
height and shaped like an inflated triangle were found
attached to basaltic substrates during a series of"Alvin"
dives at the Galapagos Rift in 1985 (Figs. 15, 16; Table
II). Capsules were attached by a basal membrane that
barely extends beyond the limits ofthe capsule chamber
Figure3. (A)ApicalviewoflenticulareggcapsulefromtheGalapagos (Fig. 16). A lateral ridge extended up from either end of
Riftwithindividualembryosvisiblethroughtransparentcapsulewall.Ar- the long axis of these capsules to meet at the capsule's
row markstheescapeaperture. Scalebar = 5 mm.bm, basal membrane. slightly off-center apex (Figs. 15, 16). Except for the
(mBe)mLbartaernael.viAerwroofwlemnatrickuslartheeggecsacpaspueleapweirtthurpee.riSpchaelrealbeaxrte=nsi5onmomf.ba(sCal) prominent lateral ridge, thesurfacesofthesecapsuleswere
Groupoffourlenticularcapsulesdrawn asthey appeared attachedtolo- smooth. Capsules fixed in 10% buttered formalin and
cation markerin Figure 1. priortofixation. Scale bar = 5 mm. subsequentlystored in ethanol, ranged incolorfrom white
HYDROTHERMAL VENT EGG CAPSULES
Figures4-5. Scanningelectron micrographsoflenticulareggcapsulewall fromGalapagos Rit't. Figure
4.Cross-sectionofcapsulewall.Scalebar = 10nm.ow.outercapsulewall;iw.innercapsulewall;si.spongy
layer. Figure 5. Cross-section through the escape aperture chamber. The outer surface ofthe capsule is
towardsthetop. Scalebar = 100/im.
toyellowish-whitetoalmost orange. Thecapsulewall was two wing-like extensions forming a saddle-shaped struc-
composedofwhatappeared tobeonespongy-fibrouslayer ture around the central oval escape aperture (Fig. 23B).
(Fig. 17). In most cases an amorphous, poorly fixed, orange em-
Each capsule contained several hundred early veliger bryonic mass, containing an indeterminate number of
larvaeapproximately 165 /urn in length by98 /urn in width, embryos, occupied the capsule chamber (Figs. 22, 23C).
as measured from electron micrographs. Larvae in all In othercases, from onetosix, but most often five, larvae
three capsules were at the same relative stage of devel- were observed through the capsule walls. The Juan de
opment and were characterized by a bi-lobed velum, an Fuca Ridge egg capsule wall consisted of two compact
apical sensory region with cephalic cilia, a mouth, a foot dense layers: an outer and an inner layer separated by a
primordium with attached operculum, and an early Pro- sharp boundary (Fig. 24).
toconch I (Figs. 18, 19). Velar compound cilia were ap- Examination of the amorphous yolk mass present in
proximately 30 urn long. The early protoconch wasover- most capsules revealed that some larval shell had been
laid by a membrane that obscured a sculpture ofradially secreted, butstructural detailswere indeterminable. Nurse
arranged rows of short tubercules intersected by weak eggs may have been present, but fixation was too poor
concentric raised ridges or lines (Figs. 19-21). Distal to forthistobedetermined. However, moreadvanced larvae
this membrane, the sculpture consisted ofparallel raised werepresent in a fewcapsules, which revealeda paucispi-
ridges runningin thedirection ofgrowth, crossed by radial ral protoconch that was large and bulbous and lacked
riblets, and forming a cancellate or net-like pattern (Fig. ornamentation other than that due to weak growth lines
19). Nurse eggs were not present in the three inflated tri- (Figs. 25, 26).
angular egg capsules.
Discussion
Juan de Fuca Ridge egg capsules Although some archeogastropods embed their eggs in
Fifty-six orange egg capsules, each shaped like an in- a benthic gelatinous mass orribbon, the majority ofshal-
mm
flated oval or pouch and measuring 3.6 0.5 in low-water archeogastropods do not produce benthic egg
length, 1.3 0.3 mm in width, and 3.6 0.7 mm in capsules(Fretterand Graham, 1962;Hyman, 1967; Rob-
heightwerecollectedduring"Alvin" Dives 1418 and 1419 ertson, 1976; Webber. 1977; Bandel, 1982; Fretter, 1984;
on the Endeavour Segment ofthe Juan de Fuca Ridge in Soliman, 1987; M. F. Strathmann, 1987). Therefore, egg
1984 (Tables I, II). Each capsule was attached to the sub- capsulesdescribed in thispaper from hydrothermal vents
strate by a flattened basal membrane (Figs. 22, 23). A are most likely the spawn ofprosobranchs ofthe higher
lateral ridge rose abruptly from the thin basal membrane orders Mesogastropoda or Neogastropoda. Various au-
mm
at either end ofthe capsule. About 2 above the sub- thors (Anderson, 1960; Amio, 1963; Bandel, 1976a, b;
stratum, the ridges at either end ofthe capsule split into Soliman, 1987) have stressed that thegeneral form ofthe
Figures6-10. ScanningelectronmicrographsofearlytrochophorelarvaeremovedfromGalapagosRifl
lenticulareggcapsules. Figure6. Ventral view showingapical plate (ap). prototroch (pt), and mouth (m).
Scalebar = 25nm. Figure7.Apical viewshowingapical plate(ap)andprototroch(pt).Scalebar = 20/im.
Figure 8. Early protoconch at extreme posterior end. Scale bar = 10 /im. Figure 9. Right lateral aspect
showingapical plate(ap). prototroch (pt), and protoconch (pc). Scale bar = 25 urn. Figure 10. Left lateral
aspectofdifferentspecimentothatshown in Figure9. Scaleasin Figure9. ap.apical plate;pt, prototroch:
pc, protoconch.
40
Figures 11-14. Scanningelectron micrographsofearlyand lateveligerlarvaeextracted from lenticular
eggcapsules from the Galapagos Rift. Figure II. Early veliger larva showing apical plate (ap), velum (v),
mouth(m). footprimordium(f),operculum(o).andprotoconch(pc).Scalebar= 25p.m. Figure 12.Apical
view ofProtoconch I in larva near hatching. Scale bar = 50urn. Figure 13. Apertural view ofProtoconch
1 in larvanearhatching.Scalebar = 25jim. o.operculum. Figure 14.Ventral viewofProtoconch I in larva
nearhatching. Scalebar = 50MHI.
41
42 R. G. GUSTAFSON KT AI.
Figure 15. LightmicrographofconvexsideofGalapagosRiftinflated
triangulareggcapsulewithembryosvisiblethroughthetransparentcap-
sulewall. Arrows mark the lateral ridges. Scalebar = 1 mm. bm. basal
membrane.
oothecae in different gastropod taxa is characteristic of
the species, and in some cases, of higher orders ofclas-
sification, and may be valuable in taxonomy. It should
benoted, however,thatsimilarcapsulesmaybeproduced Figure 16. (A) View ofthe convex side ofGalapagos Rift inflated
triangulareggcapsulewithindividualembryosvisiblethroughtransparent
by taxonomically diverse species, while in other cases in- membrane.Arrowsmarkthelateralridges.Scalebar= 1 mm.(B)Apical
terspecific variation in capsule morphology is insufficient viewofGalapagos Rift inflatedtriangulareggcapsule. Arrowsmarkthe
to differentiate closely related species (Kohn. 1961). lateral ridges. Scalebar = 1 mm. bm. basal membrane.
Galapagos Rift lenticular egg capsules
eggswith amean sizeof192.1 13.5 nm by 136.2 10.1
eMsucrFailpcaeitdtaaepene,erdtFularesenctiaiorcleualrkainridoeawgegn,cafanrpdsoumTluetrshrewiindteahoe.gaaDcseitnmrtoerpnaolsldiyoflnaomscialatineedds ncfamrpo.smuTlthehiissfracogarpmeseuDslievwee(l2l2304w3i^t1hmaonmudraxwcioitumhnuttmhoefdsi1ia0zm5ee2toeflral)ravraavneadeinfbrooontmeh
otherstatisticspertainingtoselectedlenticulareggcapsules
from these families are presented in Table III. The only
memberofthesefamiliesknowntooccurattheGalapagos
Rift hydrothermal vents is a large turrid, provisionally
described as Phymorhynchus sp. (Waren and Bouchet,
1989). A similarspeciesoccursat 13N and 21 N on the
East Pacific Rise(Turnerela!., 1985; Warenand Bouchet,
1989). Both the six egg capsules described by Turner el
al. (1985) and the five "lens-shaped" egg cases described
by Berg (1985) as characteristic ofturrids, as well as, the
lenticular egg capsules described in this paper, may all
belong to Phymorhynchus sp. from the Galapagos Rift.
Differences in reported average size between these three
groupsofcapsulesisnotunexpected, becausecapsulesize
in neogastropods is proportional to adult size. Capsule
size is also correlated with female foot width; the capsule
is formed and manipulated by the foot duringdeposition
(Robertson, 1976; Shimek, 1986).
Berg(1985)estimatedthat"lens-shaped"oothecaefrom Figure 17. Scanningelectron micrograph ofcross-section ofsingle-
the Garden ofEden and Mussel Bed hydrothermal vent layeredspongycapsulewallofinflatedtriangulareggcapsulefromGal-
sites along the Galapagos Rift contained from 500-1000 apagos Rift. The outersurfaceistowardsthetop. Scalebar = 5 ^m.
HYDROTHERMAL VENT EGG CAPSULES 43
Figures 18-21. Scanningelectron micrographs ofveligerlarvae extracted from inflated triangularegg
capsulesfrom Galapagos Rift. Figure 18. Lateral ventral view showing velum (v). apical plate(ap). mouth
(m). foot primordium (f). andearly protoconch (pc). Scalebar = 25 urn. Figure 19. Lateral viewshowing
cancellate or net-like early protoconch (pc) sculpture and obscuring membrane (me). Scale bar = 25 urn.
o.operculum: v. velum. Figure 20. Apical viewofearly protoconch. Scalebar = 20urn. Figure 21. Dorsal
viewofearly protoconch. Scale bar = 20^m.
capsules with larvae in earlierstagesofdevelopment ( 175 Although the basal diameter oflenticular egg capsules
/um in length by 100 ^m in width). The absence ofnurse described herein (14.8 X 14 mm) is larger than the 2-6
mm
eggs further suggests these capsules were laid by a turrid, ofnormal turrideggcapsules, itisnot unprecedented.
because nurseeggsare unknown intheTurridae(Table III). Egg capsules of the turrid Mangelia plicosa are 30-33