Table Of ContentReference: Biol. Bull 186: 62-71. (February,
Multiple Modes of Asexual Reproduction by Tropical
and Sea Star Larvae: an Unusual
Subtropical
Adaptation for Genet Dispersal and Survival
WILLIAM JAECKLE
B.
Smithsonian Marine Sunion at Link Port. 5f>12 Old Dixie Highway. Fort Pierce. Florida 34946*
Harbor Branch Occanoxraphic Institution. 5600 Old Dixie Highway. Fort Pierce. Florida 34946. and
Smithsonian Environmental Research Center. P.O. Box 2^. Mgemiier. Maryland 21037-0028
Abstract. Sea star larvae (Echinodermata: Asteroidea). recruit into habitats suitable for postlarval growth, de-
collected from the subtropical Northwest AtlanticOcean, velopment, and survival. Dispersal andsuccessful recruit-
exhibited three distinct modes of asexual reproduction. ment of planktonic larvae regulates, in part, the geo-
A number ofdifferent bipinnariae and brachiolariae re- graphical distribution of many benthic marine inverte-
produced by paratomous cloning of the posterolateral brates (Thorson, 1950; Mileikovsky, 1971; Strathmann,
arms. This morphogenesis was identical to that oflarvae 1974; Jackson and Strathmann, 1981; Roughgarden et
assignable tothegenus Lnidia. A second mode ofasexual til.. 1988). The arrival of competent larvae at suitable
reproduction involves the autotomization ofan anterior habitats is influenced by both abiotic and biotic features
portion ofthe preoral lobe. Primary larvae with preoral of the overlying water column (Pechenik, 1987; Strath-
lobesofvaryingsizesand free-swimming preoral lobesof mann, 1987; Young and Chia. 1987). Potential recruits
various stages of morphological development were si- can be lost to predation (Rumrill. 1990), starvation, and
multaneously collected. The free-swimmingpreoral lobes food limitation (Olson and Olson. 1989, and references
developed complete digestive systems and ultimately as- within), and todispersalaway from appropriatesettlement
sumed the form oftypical bipinnaria larvae. Asexual re- sites (Crisp. 1974; Jackson and Strathmann. 1981; Palmer
production by larvae may also take the form ofbudding. and Strathmann. 1981; Roughgarden et <//.. 1988). The
The released individual is either a blastula- or gastrula- greater the time that is required to complete the larval
stage embryo. Subsequent development to a bipinnaria- life, the more likely, in theory, that a given larva will be
stage secondary larva, with the possible exception ofcoe- lost from recruitment.
lom formation, appears to occur through the events as- Despite the theoretical disadvantages of a lengthy
sociated with normal larval development. These diverse planktonic existence, larvaeofmany marine invertebrates
methods of asexual propagation provide a common are long-lived and potentially able to disperse over large
mechanism toincreasethelength oflarval lifeandamplify geographic distances (e.g., Thorson. 1961; Scheltema,
thenumber ofindividuals. Thusasexual reproduction by 1964, 1966. 1971a. b; Scheltema and Williams, 1983).
larvae should increase the likelihood of genet represen- For example, planktotrophic larvae ofmany phyla (e.g.,
tation in the next generation. Mollusca. Sipuncula. Echinodermata. and Brachiopoda)
havebeen collected fromsurfaceplankton towsinall ma-
Introduction
jor currents ofthe North Atlantic gyre (Scheltema, 1964,
The primary ecological role ofplanktonic invertebrate 1966, 197la. b. 1975; Laursen. 1981; Rice. 1981). Schel-
larvae is to disperse away from parent populations and tema (197la) labeled these larvae teleplanic ("far wan-
dering") in reference to their potential for long-distance
Received 16 August 1993;accepted 22 November 1993. dispersal. Presumably, teleplanic larvae possess morpho-
*Current address.
Contribution #347 to the Smithsonian Marine Station at Link Port logical, behavioral, and chemical characters and character
and#998 tothe Harbor Branch Oceanographic Institution. states that decrease the likelihood of mortality during a
62
LARVAL ASEXUAL REPRODUCTION 63
W
longdispersal phase. Theselarvaeoften possessexpansive Nand 79.6 toca. 27.3 Nand 78.8 W)andat various
locomotory and feedingappendages, longelaborations of locations in the territorial waters ofthe Commonwealth
the body, and poorly calcined structural elements (i.e., of the Bahamas, chiefly in the area between the Berry
shell) (Scheltema, 197la, b; Wilson, 1978; Domanski, Islands(ca. 25.5 N, 77.5 W), Eleuthera Island (ca. 25.5
1984). These features are thought to decrease the rate of N, 76.8 W), and Andros Island (ca. 25 N, 77.5 W)
sinking and increase the volume ofwater cleared during and offGrand Bahama Island (ca. 26.5 N; 78.8 W). All
feeding. In addition to structural alterations, changes in plankton samples were taken usinga 3/4-m diameter net
the physiological state ofthe larvae may also allow foran with a 202-j/m (pore size) netting that was towed either
extended planktonic existence. Teleplanic larvae are horizontallyorvertically. Seastarlarvaeweresorted from
thought to enter a metabolic steady-state (i.e., growth the total catch as soon as possible after collection and
stasis), where the energy demands ofmetabolism covary placed in seawater that had been filtered through a bag
with the amount of ingested foods (Scheltema, 1966; or string filter (ca. 5-j/m pore size). Larvae that were
Pechenik el a/., 1984). If the total energy cost of larval maintained in the laboratory were held in finger bowls at
development is fixed for a species (Hoegh-Guldberg and 21-25C and fed a mixture ofDunaliella tertiolecta and
Manahan, 1991), then the flexibilitytovarydevelopment Isochrysisgalbana (Tahitian strain). Each day the dishes
and metabolic rates with nutrient availability may be a were inspected for newly released secondary larvae and
prerequisite for a long larval life. embryos. All asexually produced individualswerepooled
Yet adaptations that increase the likelihood that the and maintained in thesame mannerastheprimarylarvae.
genet (i.e., a genetically discrete individual) will persist With thesoleexception ofthelarvaofaspeciesassignable
can take a different and novel form. Bosch (1988) and to the genus Luidia (Bosch et al., 1989, see below), the
taxonomic classification ofthe examined larvae remains
Bosch el al. ( 1989) reported that oceanicbipinnaria larvae unknown.
ofLiiidiasp. (Ph. Asteroidea: Or. Paxillosida)reproduced
Bipinnaria larvae, brachiolaria larvae, and asexually
asexually by paratomouscloningoftheposterolateral lar-
produced individuals were processed in two ways for
val arms. Upon release, the secondary embryos morpho-
logically resemble late-stagegastrulae and rapidly assume amnorapthoomlyo,gilcaravlaeinwsepreceteioxna.miFnoredexlaivmeionratfiixoendoifnlHaorlvlalangdreorsss
the form ofyoung bipinnaria larvae. Bosch et til. ( 1989) fluid (Galigher and Kozloff, 1971) for 24 h, dehydrated
recognizedthattheabilityofa larvatoreplicateitselfmay withanascendingethanol series,andexamined usingboth
serveto lengthen the lifespan and sizeofeachgenet. These a compound and a dissecting microscope. For studies of
consequences ofasexual reproduction by larvae may en- external and internal surfaces, larvae and embryos were
(hnhfaauabncmicitbleaietttrsahteoibnfylgilk(aler1olv)niaghie-ondotcidhrsaeottaafsmniscaunecgycdetsishusseprfevudrilusvarrelae)ttcoriauomninedttmoeamfnumttlohtrieinpptlhloaiyrbicvenancgltohtlmiihf-cee wdf1riehxir.eeeddseimurnoisaiu1lnnl%gytOeCddseOhOyo:4dnarisnasttteeuhibdetsh,wetrirctasonheasaitewtetiahdotanenwroifltlo,uhriadda.nisdgTtiohcllreldiet-dsipcpwaaeallctl-ieapormdieinfnutoms-r
petence. mixture, and then examined using a Novascan 30 scan-
Further sampling has revealed that asexual reproduc- ning electron microscope.
tion by oceanic asteroid larvae in the tropical and sub-
tropical Western Atlantic Ocean is restricted neither to a
member ofthe genus Litidia nor to modifications ofthe Results
posterolateral larval arms. Plankton samplestaken in the
FloridaCurrentoftheGulfStreamand from theterritorial Field-collected bipinnaria and brachiolaria larvae ex-
waters ofthe Commonwealth ofthe Bahamas contained hibited three forms of asexual reproduction. Asexually
a number of different bipinnaria (with and without de- produced individuals were either ( 1) released as late gas-
velopingjuveniles) and brachiolaria larvae that were re- trula-stageembryosorearly bipinnaria larvae fromeither
producing asexually by one ofthree distinct modes. The or both posterolateral arms ofprimary larvae (Figs. 1, 4,
potential for asexual reproduction has now been found 6), (2) developed from an autotomized anterior region of
in representatives ofat least two different asteroid orders thepreoral lobe(Figs. 8-9), or(3)released from theapical
(reBsoesncths,a1n98u8n;usBuoaslchdeelveall.o.pm19e8n9t;alpraedsaepnttasttiuodny)toanfdurtrhepe-r tliipkseocfotnhdeitairomns(oFfipgsr.im2a,ry3,la1r4v,ae1i5n).abBlaassetudlao-nortghaestmruolra--
the existence and lifetime ofthe genet. ipthioslaosgysuamneddctohlaotraetaicohnopfatttheerntshroefetmhoedeexsamoifnaesdexulaarlvaree,-
production is exhibited by different species.
Materials and Methods
The most common method of asexual reproduction
Larvae were collected from surface waters (<60 m in observed was the differentiation ofeithera single orboth
depth)ofthe FloridaCurrentoftheGulfStream (ca. 27.3 posterolateral arms to become modified into secondary
64 W. B. JAECKLE
CO
co
' -
;
Figures 1-6. Light micrographsofasexual reproduction via paratomouscloningand buddingby field-
collected bipinnariaand brachiolaria larvae.
LARVAL ASEXUAL REPRODUCTION 65
larvae (Figs. 1, 4). This mode ofasexual propagation was forms are present (Fig. 1 1) and close examination ofthe
originally described by Bosch cl al. (1989) for larvae as- site of autotomization does not reveal any evidence of
signable to the genus Luiilia. In addition to bipinnariae mechanically induced tissue damage (Fig. 12). Collected
ofLitiiliasp., a numberoffield-collected brachiolaria lar- alongside larvae exhibiting preoral lobes ofvarious sizes
vaealso underwentasexual reproduction bymodification were a number 01 free-swimming preoral lobes that de-
oftheposterolateral larvalarms(Fig. 4; notethat members velopedacompletedigestivesystem (apparently from lar-
of the order Paxillosida do not develop a brachiolaria- val ectoderm) 1-2 days after collection (Figs. 8, 9). The
stage larva). Although the brachiolar complex was not newly released individuals retain aportion ofthecoelomic
well formed in anyasexually reproducing larva, each pos- system ofthe primary larva from which the remainderof
sessed a pair of arms on the ventral face of the preoral the secondary larva's coelomic system is presumed to be
lobe that contained an extension of the anterior larval derived (the assumed site ofautotomization is depicted
coelom; hence these are here considered to be brachiolar in Fig. 7). Secondary larvae retain the normal anterior-
arms (Fig. 5). Secondary larvae from both bipinnariae posterior polarity of the primary larvae. Although sec-
and brachiolariae are generally released as late gastrulae ondary larvae are initially asymmetrical about the
orearly bipinnariae. Many attached secondary larvae de- anterior-posterior axis (with the preoral lobe being dis-
veloped a ciliary band, and the primordium of the proportionately large; Fig. 8), their posterior region pre-
circumoral field is evident (Fig. 6). In some exceptional sumably grows at an accelerated rate and these larvae as-
individuals, primary larvae were collected with fully sume the proportions oftypical bipinnariae (Fig. 9).
formed secondary bipinnaria larvae still attached. A third method of asexual reproduction was infre-
Asexual reproduction exhibited by oceanic asteroid quently observed and involved the release and subsequent
larvae may also involve the apparent autotomization of development of a small apical portion of a larval arm.
the anterior portion of the preoral lobe. A number of The initiation oflarval budding(Figs. 2. 3)coincideswith
morphologically identical bipinnaria larvae of similar an accumulation of mesenchyme-like cells in the distal
body size (here defined as the distance between the pos- tip ofthe arm (Figs. 3, 13). The tip ofeach budding arm
terior margin ofthe larval body and the posterior margin becomes swollen and rounded (Figs. 4, 13). The tissue
ofthe preoral lobe) were obtained from a single plankton linking primary larvae to their secondary embryos (Figs.
tow taken in the Florida Current ofthe GulfStream. Al- 3, 14) regresses and the connection is lost. The newly
though the body size was similar among individuals, the released secondary individual is in a developmental state
size ofthe preoral lobe ranged from complete (Fig. 7) to that is morphologically similar to either a blastula-stage
absent (Fig. 10), with individuals intermediate between (Fig. 15) or an early gastrula-stage embryo (Fig. 16). The
the two extremes also present (Fig. 1 1 ). The loss of the apical surface ofthese cells is lined with microvilli, and
anteriormost portion ofthe larval body is probably not each cell possesses a cilium (not shown). Secondary em-
an artifact ofthe collection method because intermediate bryos have a blastocoelic space ofvariable size (Figs. 14-
Figure I. Light micrograph ofa bipinnaria larva ofLuiilia sp. (ventral view) reproducing asexually
through paratomous cloning ofthe posterolateral arms. Note the difference in appearance between the
posterolateralarmsandotherlarvalarms(L).Thesecondarylarva(C)ofthelarvalleftsideisnearthepoint
ofrelease from the primary larva. The anterior extension ofthe anterior coelom (CO) has extended well
intothepreoral lobe. E esophagus:S stomach;arrowhead ciliary band:scalebar = 65^m.
Figure2. Lightmicrographofabipinnarialarva(ventralview)intheearlystagesofasexualreproduction
viabudding. Thoselarvalarmsthatappeartobedevelopingbuds(B)differinappearancefrom nonbudding
larval arms(L). E esophagus;J developingjuvenile; M mouth; scalebar = 316fim.
Figure3. Light micrographoftheright ventralsideofalarvareproducingasexuallybydevelopingbuds
(B). CO rightsomatocoel; S stomach; scalebar = 48^m.
Figure 4. Light micrograph ofa brachiolana larva reproducing asexually via paratomous cloning of
both posterolateral arms. Thedevelopingsecondary larvae(C)differinappearance from otherunmodified
larval arms. Examination ofthe preoral lobe reveals an extension ofthe anterior coelom (CO) into an
evagination ofthe epithelium, producing a brachiolar arm (BR). S stomach; arrowhead ciliary band;
scalebar = 65^m.
Figure5. Light micrograph ofthebrachiolararm depicted in Figure4clearlyshowingtheextensionof
theanteriorcoelom (CO) intothe brachiolararm (BR). Scalebar = 29^m.
Figure6. Lightmicrographofasecondaryindividualproducedbyparatomouscloningoftheposterolateral
arms.Thedevelopingarchenteron(A)andthebeginningoftheoral vestibule(*)arevisibleinthisspecimen.
Arrowheads ciliary band ofboth the primary and the secondary larva;scalebar = 39^m.
66 W. B. JAECKLE
Figures 7-12. Light micrographs ofprimary and secondary larvae thatare involved in orthe resultof
autotomization ofthepreoral lobeofbipinnana larvae.
Figure7. Lightmicrographofaleftlateralviewofafully formedbipinnanalarvashowingthevestibule
(*). mouth (M), stomach (S). and intestine (I). Within the preoral lobe (P). the anterior extension ofthe
coelom (CO) is clearly. e\ident. The assumed plane ofautotomization is the area suggested by the space
between the open arrows. Arrowheads ciliated band: scalebar = 88/jm.
Figure 8. Light micrograph ofa left side view ofa developing secondary larva released through the
autotomization ofa preoral lobe. The digestive system is nearly fully formed. I intestine; S stomach:
mouth vestibule (*): scalebar = 70^m.
Figure9. A light micrograph ofa right side view ofa secondary larva that is moredeveloped than the
individual depicted in Figure 8. Theciliated band(arrowhead) isclearly differentiated from the othercells
ofthe larval epithelium. I intestine: S stomach; scalebar = 100fim.
Figure10. Lightmicrographshowingaventralviewofabipinnarialarvathathasautotomizeditspreoral
lobe. L larval arm; M mouth; scalebar = 158^m.
LARVAL ASEXUAL REPRODUCTION 67
16, 20) and within the blastocoel there can be a variable larvae, which possessstructural, physiological, and repro-
number of mesenchyme-like cells (Figs. 14-16, 20-21). ductive characteristics to prolong larval life, can disperse
Ifthe secondary embryo is released in a blastula-likecon- greatdistancesand recruit intohabitatsfarfromthesource
dition, thecellsofonesideofthesecondaryembryobegin population (Scheltema, 1971a. b).
to invaginate into the blastocoelic cavity (Fig. 16), ulti- Discussions ofthe ecology ofteleplanic larvae largely
mately resulting in the formation ofa gastrula-like sec- center on the velocity of the prevailing ocean currents
ondary embryo (Fig. 17). Development ofthe mesoderm and the adaptations (e.g.. increased size of the feeding
of the secondary larva has not been directly observed. structures, decreased weight of inorganic structural ele-
Thuscoelomicdevelopment could occureitherfrom out- ments, and growth stasis) that increase the probability of
pocketingsofthedevelopingarchenteron or from the pool survival (e.g., Scheltema, 1966; Pechenik et at., 1984).
ofmesenchyme-like cells that preexist within the blasto- Thorson (1961) believed that "long-distance larvae seem
coel and accumulate at the distal tip ofthe archenteron only to occurin special groups ofprosobranchs and crus-
(Figs. 15-18, 20-21). As development proceeds, the cells taceans" and doubted that echinoderm larvae were ca-
oftheouterepithelium become thinner in profile and the pable of transoceanic dispersal. Thorson did, however,
embryo elongates (Figs. 16-18). The developing archen- note the observations of Mortensen (1921; p. 147-149)
teron comes in contact with the outer epithelium and a on an ophiopluteus larva (Ophioplutcus opulentiis) that
secondary opening, the mouth, is formed. Theentire pro- apparently released a benthicjuvenile and then returned
cess (from release to a feeding individual) requires 24- tothewatercolumn. This larvasubsequently regenerated
36 h. In addition toelongation, thedevelopingindividual both the ciliary bands and the posterior digestive system
develops the ciliated bands and overall morphology ofa and ultimatelyassumedthemorphologyofanormal larva.
bipinnaria larva (Figs. 18, I1)). Thorson suggests that "some tropical ophiurans and per-
haps some tropical asteroids may have chances to cross
Discussion even the widest ocean basins, provided that Mortensen's
observations on the 'budding larval polyps' holds true."
A majorityofmarineinvertebratesproduceplanktonic The resultsofpreviousstudies(Bosch, 1988; Bosch etal.,
larvaethatremain inthewatercolumn forvariableperiods 1989) and the present study reveal that asexual repro-
oftime. This obligate dispersal period allows for (1) re- duction by echinoderm larvae exists and is not restricted
cruitment into sympatric populations, (2) maintenance solely to the ophiurans.
ofgeneticcommunication between allopatric populations, All modes of asexual reproduction described in this
and (3) colonization of new or recently opened habitats report involvea serial dedifferentiation and redifferentia-
(e.g., Thorson, 1946, 1950; Scheltema, 1971a, b; Milei- tion oflarval tissue. In all three modes the primary de-
kovsky, 1971; Crisp, 1974, 1976; Chia, 1974). Dispersal velopmental cycle (egg-* embryo larva) isoverlapped
increasesthe probability that a species will persist in both by a new developmental series (primary larval tissue
ecological and geologic time scales (Jablonski and Lutz, secondary embryonic tissue secondary larval tissue).
1983). However, these positive benefits of a planktonic In secondary larvae produced by all observed modes of
larval stage are countered by the increased likelihood of asexual reproduction, it appears that the "endodermal"
larval mortality with extended time in the plankton regionsare derived from the primary larva'sdifferentiated
(Vance, 1973, 1974; Strathmann, 1974, 1985; Jackson ectoderm. Further, theconcordancebetween theposition
and Strathmann, 1981: Young and Chia, 1987; Rough- ofthe putative mesenchyme-like cells and the coelomic
garden el at.. 1988). Much recent work on the ecology of cavitiesinsecondary larvae, producedeitherby paratomy
invertebrate larvae has been centered on coastal larval orbudding, suggeststhat these cellsare responsible foror
forms(e.g., see Young, 1990). Dispersal away from neritic assist in the production ofthese mesodermal structures.
watersbylocalcirculation patternssignificantlydecreases The process ofasexual reproduction differs among the
the likelihood ofsuccessful recruitment for coastal larval three modesdescribed in this report. Thesedevelopmental
forms (Roughgarden et ai. 1988). In contrast, teleplanic differences, coupled with the fact that larvae from at least
Figure 11. Lightmicrographofabipinnarialarvawithapreoral lobe(P)ofintermediateheight(dorsal
view, plane offocus is midfrontal). The connection between the left and-right anterior coeloms (CO) is
visibleimmediately anteriortothemouth (M). Scalebar = 62^m.
Figure 12. Light micrograph ofa higher magnification view ofthe larva shown in Figure 10. The
M
smooth surface ofthe site ofapparent autotomization is denoted by the arrowheads. mouth: scale
bar = 91 nm.
68 W. B. JAECKLE
17
13
rCnO
'
15
>
*
16
LARVAL ASEXUAL REPRODUCTION 69
Figures 20-21. Scanning electron micrographs ofthe exterior and interior surfaces ofnewly released
secondaryembryos.
Figure 20. Scanningelectron micrograph ofablastula-stageindividualthat hasbeenbrokenopen.The
epithelium (E) iscomposed primarily ofciliatedcolumnarcells, but circularholessuggestthat at least one
othercell type ispresent. The blastocoelicspace is filledwith cells: in this micrograph small spherical cells
(S)are notable. Scalebar = 28^m.
Figure 21. Scanning electron micrograph ofthe basal face ofthe outer epithelium ofa blastula-stage
embryo. Present are mesenchyme-like cells (M) and smaller spherical cells (S). The inner surface ofthe
epithelium islinedwith a fibrous meshwork. Scale bar = 9jim.
Figures 13-19. Lightand scanningelectron micrographsthat depict thesequenceofeventsduringthe
processofasexual reproduction by budding.
Figure 13. Light micrograph showingtheroundedappearanceofthearmapices(B)andtheassociated
accumulation ofcells(*). Scalebar = 58^m.
Figure 14. Light micrograph ofabud nearthetimeofreleasefrom theprimary larva. Thesiteofbud/
larvajunction isdesignated bythearrow. Scalebar = 38^m.
Figure 15. Light micrograph ofa released bud in a blastula-likecondition. In thisindividual, the cell-
freeblastocoel(b)issmallandtheblastocoelicspacecontainsalargenumberofcells(*). Scalebar= 33urn.
Figure 16. Light micrograph ofa free-swimming secondary embryo undergoing gastrulation. The de-
velopingarchenteron (closedarrow)isformed bytheinvaginationoftheepithelium intotheblastocoel(b).
Blastopore BL; scalebar = 25Mm.
Figure 17. A light micrograph showing a fully formed gastrula-stage secondary embryo produced by
asexual reproduction bybudding. Thewell-developed archenteron (filled arrow) leadsfrom theblastopore
(BL) into the blastocoel (b). The accumulation ofcellsatthe apex ofthearchenteron (*) is seen in many
individualsand maybeinvolvedintheformationofthecoelomsofthesecondarylarva.Scalebar=27nm.
Figure18. Alightmicrographofadorsalviewofanewlyformedsecondary bipinnarialarva.Theciliated
band (arrowhead) has formed and the primordium ofthe coelomic system ofthe secondary larva (CO) is
clearlyevident attheanteriorextent ofthedevelopinglarval gut(filled arrow). Scale bar = 23>im.
Figure 19. Scanningelectron micrograph ofa fully formed secondary bipinnaria larvathat developed
from a bud released from a primary larva. Anus A: mouth M; ciliated band (filled arrow): scale bar
70 W. B JAECKLE
twoordersare reproducingasexually(members ofthe or- (R/V SeaDiver). Special thanksareextendedtoDr. Mary
der Paxillosida (e.g., Liiufm) do not develop a brachiolar Rice and her staff(Woody Lee, Sherry Reed, and Hugh
complex), suggest that asexual reproduction represents an Reichardt) for collecting and allowing the author to ex-
adaptation to a prolonged planktonic existence. However, amine plankton samples taken for her research program.
the factor or factors that regulate the production ofsec- Dr. Sid Bosch (SUNY, Geneseo) and Ms. Elizabeth Balser
ondary larvae remain obscure. (Clemson University) are acknowledged for their stimu-
Despite the theoretical advantages of persistence and latingdiscussionsaboutthedevelopmentofasteroidechi-
amplification ofthegenet, asexual reproduction may have noderms. Ms.Julianne Piraino(Smithsonian MarineSta-
a negative impact on the primary larvae. All forms of tion at Link Port) helped prepare the scanning electron
asexual reproduction require a relatively small percentage micrographs. The work was support by a Smithsonian
ofthe total larval soma, but may significantly reduce the Postdoctoral fellowship to W. Jaeckle and by NSFgrants
effectiveness of larval feeding. In paratomous cloning OCE-8916264(toC.M. Youngand K.J. Eckelbarger)and
(mode 1), each posterolateral arm iscompletely modified OCE-91 16560 (to C.M. Young).
to produce a secondary larva. Although this arm pair is
at the posterior margin of the larval body, it may con- Literature Cited
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food particles captured. Hart (1991) reported that the Bosch, I. 1988. Replication by budding in natural populations ofbi-
posterior region ofthe body ofbipinnaria larvae ofDer- pinnarialarvaeoftheseastargenusLiiidiu. Pp. 789 in Echinuderm
maslerias imbricata accounted fornearly aquarterofthe Biology:ProceedingsojtheSi\thInternationalEchinoderm Confer-
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