Review of the Predators and Parasites of Stony Corals, with

Special Reference to Symbiotic Prosobranch Gastropods'

ROBERT ROBERTSON2

ABSTRA CT: Predators and parasites on the living tissues of stony (scleractinian)corals include bony and carti laginous fishes, asteroids, crustaceans (cyclopoid cope­pods, cirripedes, and brachyuran crabs) , polychaetes, and gastropods (prosobranchsand nudibranchs). These are all facultative predators except the crustaceans andgastropods that are obligately associated (symbiotic) with and feed on their coralhosts. Such symbionts are known in four unrel ated families of crustaceans (Xa rifi­idae, Asterocheridae, Balanidae, and Xanthidae) and four unr elated families ofprosobranch gastropods (Architectonicidae, Epiton iidae, Ovulidae, and Corallio­philidae) . . A fifth prosobranch family includes frequent but not obligate coralassociates that are coral- and possibly also mollu sk-feeders (Muricidae [Dl'llpa,subgenus DmpellaJ). The eolid nud ibranch genus Phestilla (Tergipedidae) in­cludes the only so far identified opisthobranchs definitely symbiotic with corals.Most of the crustacean and molluscan symbion ts live with hermatypic corals inthe Indo-Pacific. Specificity to particular genera or families of corals is low, butthe bright yellow, orange, or pink phases (species? ) of the dendrophylliid aher­matypic coral Tubastraea are host to similarly colored prosobranchs C Epitonitlm" )and a nudibranch (Phestilla melanobrachia) . Adaptations for feeding on coelen­terates are various, but in unrel ated gastropod famil ies similar specializations occur(cuticularized esophaguses and proboscises, ptenoglossate-like radul ar teeth, andtotal loss of radulae) . The most specialized of the coral-dwelling prosobranchsare the coralliophilids ( including MagiltlS), parasites without radulae living bothon and in coelenterates.

COELENTERATES and in particular stony (scler­actinian [madreporarian] ) corals have beenthought to be nearly immune from predators(W ells, 1957, p. 612) and parasites. Nemato­cysts presum ably are a deterrent. However, itit has been discovered, principally in the lastdecade, that various animals do feed on theliving tissues of coelenterates, and that a feware specialized predators or parasites of stonycorals.

FISHES

Bony fishes in twelve famil ies are reportedto feed on corals. Many of these fishes eitherremove the living coral tissues or abrade deadcoral skeletons for their attached or contained

1 Manuscript received May 9, .1969.~ Academy of N atu ral Sciences of Phil adelph ia.

Philadelphi a, Pennsylvania 19103.

43

algae (Cloud, 1959, pp . 398-399, pls, 130­131) . The nine families that definitely includefrequent to occasional facult ative predators onliving corals are the Ephippidae (spadefishes) ,Chaetodontidae (butterffyfishes) , Pomacentridae[or Abudefdufidae] (damselfishes) , Labridae(wrasses) , Scaridae (parrotfishes) , Acan­thu ridae (surgeonfishes), Balistid ae [includingMonacanth idae] (trigger- and filefishes) ,Tetraodontidae [including Canthigasteridae,Lagocephali dae, and Colomesidae] (puff­ers) , and Diodontidae (porcupinefishes)[Quoy and Gaimard, 1824--1825, pp. 201- 202,600- 601 ; Al-Hussaini, 1947, pp . 34--39; Go­har and Latif, 1959; Le Danois, 1959 ; Hiattand Strasburg, 1960, pp. 91, 101, 113-11 4,etc.; Talbot, 1965, p. 456; Randall, 1967, pp.828-830] . The three additional fam ilies thatpossibly include such predators are the Ky­phosidae (sea chubs) [Gerlach, 1960, p. 362] ,

44

Cheilodactylidae [Squires , 1964], and Ostra­ciidae ( trunkfishes) [Hesse, 1924, p. 229;Al-Hussaini, 1947, p. 36] . Several of theoccasionally predatory families (e.g. , the Acari­thuridae) are primarily herbivorous.

A cartilaginous fish feeds on corals in theRed Sea: Gohar and Mazhar ( 1964a, p. 9 )found "parts of corals mainly Styloph ora" inthe stomachs of the nurse shark N ebrins COIl ­

color RiippeU (Orectolobidae). "The teeth aresmall and adapted for snapping the corals andsmall sand-living invertebrates" (Gohar andMazhar, 1964b, p. 149). This nurse shark alsofeeds on fishes and cephalopods.

INVERTEBRATES

Goreau ( 1964) has described how the largespiny Indo-Pacific asteroid Acanthaster planci(Linn.) feeds on coral tissues, and suddenlyincreased populations of this starfish recentlyhave been devastating corals on the GreatBarrier Reef, Australia, and elsewhere in thewestern Pacific (Barnes, 1966; Chesher , 1969;Paine, 1969 ; Weber, 1969) . Goreau ( 1964)also reviewed some of the other animals thatfeed on corals. The invertebrates are nowknown to include the amphinomid polychaeteH erm odice carnncuiata (Pallas) [Marsden,1962; Glynn, 1963; Marsden, 1963a, 1963b] ,the xarifiid cyclopoid copepods (Gerlach,1960, p. 360, 362; Humes, 1960 and subse­quent papers , including Humes and Ho, 1968),the asterocherid cyclopoid copepod Cholomy­zon (Stock and Humes, 1969), the balanidcirripede Pyrgoma montlculariae Gray [Rossand Newman, 1969], the majid crab M ith­raculus sculpt«: (Lamarck) [Glynn, 1963],and the xanthid crabs Trapezia and T etralia[Knudsen, 1967]. All these inverteb rates defi­nitely feed on the living tissues and mucus ofcorals, either as facultative predators or asobligate parasites (all the crustaceans listedexcept the M ithraCtlIIlS). The barnacle genusPyrgoma, always associated with stony corals,includes nonpa rasitic, semiparasitic and wholl yparasitic species (Ross and Newman, 1969 ) .Excluded from consideration here are the manyother crustaceans associated or "commensal"with corals (Patton, 1966), and the sponges,bivalves, cirripedes, sipunculids, and poly-

PACIFIC SCIENCE, Vol. 24, January 1970

chaetes that bore or live in holes in coral skele­tons. Other amphinomid polychaetes possiblyare like H erm odice in feed ing on corals (Ebbs,1966, p. 547).

GASTROPODS

Among the many marine gastropods thatconsistently are associated (symbiotic) withcoelenterates, there are some living with stonycorals that definitely feed on the living tissues.Since even the existence of such gastropods islittle known among marine ecologists, this pa­per reviews in detail the kinds of gastropodsinvolved and what little is presently known orcan be inferred of their modes of life. Gardi­ner ( 1902, p. 338) seems to be the first tohave observed that a few (unspecified) gastro­pods "make a practice of consuming [coral]polyps, leaving dead tracks over the otherwiseliving colonies."

Many of theeolid nudibranchs, the mostrenowned gastropods that feed on coelen­terates, are able to select and extract undis­charged nernatocysts f rom the coelenterate(mainly hydroid) tissues that they swallow, toposition these in their own bodies (in theircerata), and to use them for their own de­fense against pred ators (Edmunds, 1966, andreferences there in). Risso-Dominguez ( 1964,p. 235) avers "that most groups of coelen­terates . . . have typical and taxonomically welldefined eolid predators." Few eolids symbioticwith stony corals are known so far, and theonly two identified are in the tergipedid genusPhestilla. Th e unidentified bright orange eoliddiscussed and figured by Edmondson ([1933?]1946, p. 184, fig. 97b) as being associatedwith and feedin g on D endr oph yll ia manni(Verrill) [=Ttlbastraea aurea ( Quoy andGaimard )] has been shown by Harris ( 1968 ) ,with help from Dr. Kikutaro Baba, to bePhestilla melanobrachia Bergh , a species wide­spread in the tropical western Pacific and obli­gately associated with Tubastraea and otherdendrophylliids. This large eolid is polychro­mat ic, individuals being orange, pink, or pre­dominantl y greenish-black depending whetherthey have recently been feeding on orange,pink, or greenish-black Tubastraea. (The threedifferentl y colored species of Tubastraea men-

Predators and Parasites of Stony Corals- Ro BERTSON 45

tioned by Harris are believed by Boschma[1953] all to be phases of T . aurea.) Harrissuggests that the pigment in the nudibranch isbiochemically the same as in the coral, andHarris has observed that this Phestilla does notstore nematocysts. Edmondson ([1933?] 1946,p. 184) also mentioned a second unidentifiedeolid with Porites euermanni Vaughan, thenudibranch leaving "smooth patches on thecoral heads where it has destroyed the polyps."Harris informs me (in litt.) that Edmondson'ssecond species was Phestilla sibogae Bergh ,which feeds on Porites exclusively, and thatA eolidia edm ondsoni Ostergaard (1955, pp .133-135, fig. 16, pI. 1) , believed by Oster­gaard to feed on the polyps of Porites com­pressa Dan a, is a synonym. Harris also informsme (in litt.) that he twice has collected a verysmall, as yet unidentified, eolid that feeds ona M ontipora at Singapore, and that at the samelocality a fourth eolid lives on Gonioporu.

The only non-eolid nudibranch so far re­ported to feed on corals is the porostomatousdoridoid Phyllidia bourgini Risbec, found verycommonly on A cropora (also millepores) byVicente (1966, pp . 105, 128) off the south­west coast of Madagascar . The Phyllidiidae havea large muscular pharynx but neither jaws nora radula. Vicente gave no details, and accord­ing to Harris (i n litt.) all the phyllidiids withwhich he is familiar feed on sponges. Vicente'sreport therefore needs confirmation.

The diversity of shell -bearing prosobranchssymbiotic with coelenterates is reflected in thenumber of symbiotic genera now known : 26,in eight families (Robertson, 1966, 1967, andnew cases reviewed or reported herein). Manyof these gastropods are known to feed on theirhosts, which besides stony corals include hy­droids, stylasterine hydrocorals, discophores,siphonophores, gorgonians, soft corals (al cyona­rians) , black corals (antipatharians), zoanthids,and actiniarian sea anemones. Four unrelatedfamilies and nine genera are definitely knownto include species symbiotic with stony (scler­actinian) corals. These families and generaare: Architectonicidae (Philippia) , Epitoniidae(Epitonism, s.l.) , Ovulidae (Jenneria and Pedi­atlaria) , and Coralliophilidae (C oralliopbila ,Quoyllla, Leptoconcbus, Magi lopsis, and Ma­gilllS) . Drupella, a subgenus of Dmpa (Mu-

ricidae), feeds on corals but is not consistentlyassociated.

Architectonicidae ["Solariidae" +Heliacidae}

In the Hawaiian Islands, Pbilippin (Psilaxis)radiata (Reding) lives near Porites lobataDana and has been seen to feed at night onthe polyps (see the following article in thisissue: Robertson, Scheltema, and Adams,1970). Other species of Philipp ia probablyhave similar habits.

Epitoniidae ["Scalidae" + "Scalariidae"}

Many wentletraps live with or forage forthe actiniarian sea anemones on which theyfeed, but a few have other coelenterate hosts.The following five shallow-water species areknown to live with corals : Bpitoninm costa­latnm (Kiener) under Ftmgia sp. in the south­western Philippines (Robertson, 1963, pp . 57­58, pI. 5, fig. 4 [the identification is now defi­nite; I since have seen the holotype in Ge­neva]); Epitonium ul« Pilsbry under Fllngiascutaria Lamarck in the Hawaiian Islands(Bosch, 1965) , and the chrome yellow "Epi­ionium" billeeana (DuShane and Bratcher,1965) [DuShane, 1967] with the brilliantorange and yellow phase of the aherma­typic dendrophylliid Tubastraea tennilamellosn(Milne-Edwards and Haime) [a probablesynonym of T. anrea according to Boschma(1953)] in the Gulf of California. Thisepitoniid is the prosobranch counterpart of thebright orange phase of the nudibranch Phes­tilla melanobrachia discussed earlier . In theMaldive Islands, a closely related, crypticallycolored "Epitonium" lives with the same colorphase of T ubastraea aurea [Harris informs me(in litt.) that he has collected a similarepitoniid with T. aurea at Singapore and inthe Philippines, and with a pink dendrophyl­liid at the Great Barrier Reef, Australia] , anda species similar to but definitely different fromEpitonium uln lives under Fll1lgia jmtaria[Robertson, 1966, ·as "A maea sp." and "Epi­toninm sp." and unpublished observations] .

There have been no direct observations onthe feeding of any of these five species, but

46

Bosch provides good indirect evidence that indarkness Epitonium ult: feeds on the livingtissues of Fll1lgia scntaria. Bosch saw tissuelesions on the coral and found zooxanthellaeand nematocysts in the viscera of the wentle­trap; also "wentletraps placed near coralswhich had been stained with a vital dye (neu­tral red) soon became suffused with the samecolor due to the ingestion of dyed coraltissue." Bosch believed that Epitonium ul« cangrow from a larva to sexual matu rity withinthe remarkably short time of three weeks, andMr. Eric Guinther (unpublished) recently hasconfirmed that this can occur even within twoweeks.

All the coral-associated wentletraps arelikely to feed on the soft tissues of their hostsin the same way as the species that feed on seaanemones: by everting a long acrembolic pro­boscis and swallowing large pieces of flesh(such as whole tentacles) that are pinched offand pulled into the esophagus with the radula.

Ovulidae ["Amphiperatidae" +"Pediculariidae"]

This fairly small family , allied to the cowries(Cypraeidae), is probably comprised entirelyof symbionts that feed on coelenterate hosts.Gorgonians and alcyonarians are the hosts ofmost of the genera, and only Jenneria andPedicularia are known with stony corals.

[enneria pttstnlata (Lightfoot) , endemic tothe tropical eastern Pacific and the only livingspecies in the genus, according to D'Asaro(1969, p. 182) "is a hardy species normallyfound in association with the stony corals uponwhich it feeds." Specimens from Panama weretaken live to Miami, Florida, and were main­tained there in aquaria for three years byD'Asaro. There they fed on the ahermatypiccoral Phyllangia americana Milne-Edwards andHaime, and the hermatypic corals Siderastreasiderea (Ellis and Solander) and Porites sp.,showing a marked preference for Phyllangia.The :familial placement of Jenneria has beenin doubt, but D 'Asaro has shown that it be­longs here.

Pedicularia demssata Gould was reported byDall (1889, p. 237) on the ahermatypic and

PACIFIC SCIENCE, Vol. 24, January 1970

colonial caryophylliid coral Solenosmilia vari­abilis Duncan from 450 fathoms off northwestCuba. Pedicularia is known otherwise onlywith stylasterine hydrocorals (the commonesthosts) , gorgonians and unspecified "madre­pores" (Hedley, 1903, p. 343 ; Berry, 1946) .

Muricidae

This is a large family that includes the oys­ter drills . Tropical species in various muricidgenera sometimes occur on living corals. Mostsuch associations are happenstance and tem­porary except in the case of D rup ella, a sub­genus of D rup« restricted to the Indo-Pacific.In Micronesia, D1'1Ipa (D1'1Ipella) rllgosa(Born) and Drupa (Dmpella) cornus Redingboth occur "exclusively on living coral,"D1'1Ipa cornns "most frequently on Porites sp.,but also on Stylophora sp. and Seriatopora sp."[Demond, 1957, pp . 311-312, as M01'1lla con­catenata (Lamarck) and M . elata (Blainville),respectively]. Likewise at the Cocos-KeelingIslands, Indian Ocean, Maes (1967, p. 130)found D1'1Ipa comus "only on living corals,"on both "massive and branching corals of sev­eral species . . . . A large colony was foundon a branching Montipora . . . ." In the CookIslands, D rupa cornns has been collected on abranching Acropora. In some other areas,Drup« comus occurs on substrates other thanlive corals (Cernohorsky, 1969, p. 304) . Inthe Maldive Islands, southern India, Ceylon,and Tahiti, I have personally collected the spe­cies on and under rocks and dead corals onreefs (even under turfs of green algae), butin the Maldives I also found it in colonies inthe clefts of branches of live Pocillop ora.Drup« cor171IS never is far from live coral andperhaps is associated only for feeding. A thirdspecies, Drupa (D mpella) ocbrostoma (Blain­ville ) , less often occurs on corals and livesmainly on and under rocks.

Drnpella radulae are unlike those of allother muricids in having long, slender, basallydenticulate laterals with hooked and usuallybifid tips [Arakawa, 1958, D1'1Ipa 1'1Igosa asDrnpella frag1l1n (Blainville); 1965, p. 117;Cernohorsky, 1969, pp. 303-307, figs. 8-11] .Cooke (1895, pp. 222- 223), Arakawa , andWu (1965, p. 102) have attributed these struc-

Predators and Parasites of Stony Corals-RoBERTSON 47

tural adaptations to specialized feeding habits,and have implied that D rup ella species feedon the living tissues of their coral hosts. Fank­boner (personal communication) has stud iedthe feeding and functional morphology of thegut of Drupe C01'11t1S (or "Momla elata" ). InHawaii it consistently lives on Pocillopora and

.Porites compressa and feeds nocturnally onthe polyps. Th ere is a long pleurembo lic pro­boscis that is cuticularized exteriorly. An en­larged pedal gland secretes mucus masses thatduring feeding are pushed ahead of the mouth.Th e cuticularization and mucus presumablypreven t injury from nematocysts. Fankbonerdescribes the action of the radula. The coraltissue is liquefied extracorporeally by ejectedsalivary secretions; thus the food is ingestedin a fluid state. Unexp loded nematocysts occurin the gut and even the zooxanthellae fromthe coral tissue are digested. The stomach isatypical of stenoglossans. Fankboner foundthat Drup« COr11llS would not feed on FlIngiaor dendrophylliid corals.

Drup ella possibly also feeds on prey otherthan corals. As mentioned earlier , the occur­rences with corals are inconsistent. Th ere arepresumably reliable observations of them feed­ing on mollusks. Drupe C01'11US was reported byRisbec [193 2, as Ricinuls chaidea (Duclos) , aname that has been misapplied to male D rupecomus according to Cernohorsky ( 1969, pp.304-305) ] to have dr illed a small oyster, anda group to have attacked and partly eaten aliving Strom bus without drilling it. Accordingto Taylor ( 1968, pp . 157, 173), but withoutdetails, Drupe ocbrostoma is also mollusciv­orous.

Coralliophilidae CMagilidae" +"Rapidae"J

This fairl y small family, supposedly derivedfrom the Muricidae, is reputed invariably tolack jaws and radulae (Ca rus, 1837, p. 197;Th iele, 1929, p. 300; Abbott, 1958, pp. 65­67 ; Gohar and Soliman, 1963 , p. 106 ; W ard,1965, p. 447). Excepting several species ofCoralliophila living with gorgonians and zoan­thids, Rbizocbilus with antipa tharians, Latiaxiswith gorgonians (and other hosts?) and Rapaembedded in alcyonarians, all coralliophilids

on which there is any information as to modeof life occur with stony corals. Various speciesof Coralliopbila and the genera Qtl0y"la,Magilopsis, Leptoconcbus, and Magiltls arehost-specific to stony corals (Leptoconcbus pos­sibly also to millepores). The four coral­specific genera are restricted to the Indo-Pacificand are derived from Coralliophila-like ances­tors that lived externally on corals and hadregularly coiled shells. Qtloyttla has a limpet­like shell adapting it for external life oncorals; Magilopsis and Leptoconcbus are ovoidand bore holes into corals, and MagiltlS be­comes uncoiled and is sessile inside corals.

The coral-dwelling species of Coralliopbilaare all external, either on branched corals orin crevices on massive corals (often at the edgeof a living colony) . The coral substrate be­neath them is always scarred (the foot appearsto secrete a thin layer of calcium carbonatebeneath it ) , and they appear never to movefrom their scars as do limpets. Incrusting or­ganisms (vermetids, etc.) occasionally attachthem to their coral substrates, and the gastro­pods still thr ive when th is happens. C. viola­cea (Kiener r.s the most abundan t Indo-P acificspecies, has been reported on Porites at theCocos-Keeling Islands, Ind ian Ocean (Maes,1967, p. 133, pl. 2, fig. B) , in Micronesia(Demond, 1957, p. 315), and at ClippertonIsland in the eastern Pacific (Hertlein and All i­son, 1960, p. 16). I have personally collectedCoralliopbila violacea in the Maldive Islandson massive Porites. The species is not specific toPorites, however. At Tahiti , I collected it ontwo genera of corals (unfort unately not col­lected or identified) . At the Cocos-KeelingIsland s, Indian Ocean, Coralliopb ila erosa(Reding ) lives on branching Acropora andMontipora [Maes, 1967, p. 133, pl. 2, fig. C,as Coralliophila dejormis (Lamarck) , a syn­onym of C. erosa according to Abbott ( 1958,p. 66) ] . At Barbados, W est Indies, Coralli­ophila abbreuiata ( Lamarck) lives on MOI/ ­tastrea annnlaris (Ellis and Soland er ) [Ward,1965] . At Great Abaco, Bahama Island s, Ihave personally collected Coralliopbiln abbre-

3 Abbo tt (1 958, p. 66 ) has suggested that this isa synonym of Coralliopbila erosa (R eding) , but heseems to have lumped at least two species.

48

viata singly, in pairs, and in colonies on andunder Acropora palmata [(G. Fischer)?] (La­marck) and under and near the edge of matsof Diploria clivosa (Ellis and Solander) . In thecollection of the Academy of Natural Sciencesof Philadelphia, there are specimens of Coral­liophila abbr eviata from the Florida Keys andGuadeloupe that were also with Acropora pal­mata, and at British Honduras I collected itwith Favia fragttm (Esper). Coralli ophila cari­baea Abbott (1958, pp . 66-67) lives mainlywith gorgonians, but at Great Abaco (BahamaIslands) I have also found it on and underlive and dead .corals (Acrop ora palmata andDiploriacliv osa, the same hosts as for Coral­liophila abbre viata in the area).

In mode of life, Qttoyttla is similar to Coral­li ophila. Q!,oyttla substrate scars are smoothperipherally (opposite the shell) and level,and minutely but deeply furrowed under thefoot. These numerous furrows bear no relationto the microstructure of the coral skeleton , andthey tend to anastomose and parallel one an­other. The foot appears to be permanently at­tached. According to Maes (1967, pp . 133­134, pI. 2, fig. D), Qttoyttla madre porarnm(Sowerby) " is apparently restricted to coralsof the family Pocilloporidae" ; she recorded itfrom Madagascar with Seriatopora and at theCocos-Keeling Islands , Indian Ocean, found itonly with two species of Pocillopora. Qtt oyttlamadrep orarnm also occurs "imbedded in" Po­cillopo ra in the eastern Pacific at ClippertonIsland (Hertlein and Allison, 1960 , P: 16). Ihave personally collected it in the MaldiveIslands on Pocill opora branches and in theclefts between branches. In the Academy collec­tion there are also specimens of Qttoy!tla ma­dr eporamm collected on Pocillopora at NewCaledonia, Fiji, the Cook Islands , and the Pa­cific coasts of Mexico and Nicaragua. However,Demond ( 1957, p. 316) records Qttoy!tla tna­d rep orarum in Micronesia with M ontipora(A croporidae) as well as Poeillopora andStylophora (Pocilloporidae) . Qtt oy!tla m ono­donta (Blainville) is recorded in Micronesiawith Pocillopora, Seriatop ora, St ylophora, andbranching Porites (Demond, 1957, p. 316) ,and in the Seychelles with Porites nigrescensDana (Taylor, 1968, p. 169, as " Q!,oyala" ) .Maes (1967, pp. 133-134, pI. 11, figs. B-C)

PACIFIC SCIENCE, Vol. 24, January 1970

has shown how Q!loYllla develops differentgrowth forms depending on the species of hostcoral. Qll oyttla madre porarum probably is anecotypic form of Q. monodonta (the sculpturaldifferences mentioned by Demond are incon­stant) .

The three genera dwelling internally incorals are closely related. Leptoconcbus hasbeen thought to be juvenile M agilus, but Goharand Soliman ( 1963) have shown that sexualmaturity occurs in both Leptoconcbus andM agilopsis. Adult L eptoconcb us supposedly al­ways lacks an operculum while both M agil opsisand M agillls retain an operculum (Carus, 1837,figs. 5-6, a1 ; Gohar and Soliman, 1963, p.104) . The possibility that Ma gilllS is a growthform of Lep toconcbus and/or M agilopsis is stillnot excluded because the MagilllS form mightdevelop only in fast-growing corals. Accordingto Gohar and Soliman (1963) , both Lepto­concbu s and M agil opsis bore mechanically intoliving coral skeletons . A burrow is connectedto the exterior only by a small opening op­posite the anterior siphon of the gastropod,which is always situated apex down . ProfessorJohn W . Wells has observed ( in litt.) thatLeptoconcbns burrows are usually at one endof a stomodaeal slit (i .e., near the mouth ofa polyp). M agilops is lamarckii (Deshayes) isrecorded in A cropora at the Tuamotus and inGoniastrea retijormis (Lamarck) in the Ma­rianas (Morrison, 1954, p. 14; Demond, 1957,p. 317; Cloud , 1959, pp . 391-392, pI. 129,figs. D-E), and in Cyphastrea and rarely M on­tipora in the Red Sea (Gohar and Soliman,1963). From Madagascar , there are specimensof Ma gilopsis lamarckii in the Academy col­lection that were found in a massive Porites.L eptoconcbns cmningii Deshayes is recorded(erroneously? ) in M illepora at Mauritius(Martens, 1880, p. 238) , and in Favia stelli ­gera (Dana) and Goniopora in the Red Sea(Gohar and Soliman, 1963) . Leptoconcbusglo bulos«: Sowerby is recorded in Goniastreaand Echinopora in the Red Sea (Gohar andSoliman, 1963, as Leptoconcbus "gl obosusDeshayes") .

In form and habit , M agilus antiqnns Mont­fort ( the only species in the genus ) is the mostspecialized coral symbiont among prosobranchs.The juvenile shell is coiled and remarkably

Predators and Parasites of Stony Corals- RoBERTSON 49

variable in size and shape, while the th ickadult shell is an uncoiled, irregular tube deeplyembedded in a living coral skeleton but withthe aperture at the surface. The coiled apexand par t of the tube become completely cal­cified internally, while distally the apertu rekeeps pace with growth of the surroundingcoral (Carus, 1837; Lamy, 1924) . M agi/lISantiquns has been collected together withM agilopsis lamarckii in Goniastrea retif ormisin the Marianas (Demond, 1957, pp . 316- 317,fig . 25; Cloud, 1959, p. 392, pI. 129, figs. A­B). In the Academy collection there are speci­mens embedded in Platygyra and/or Leptoriafrom Mauritius and the Bismarck Archip elago.Carus ment ioned ( 1837, pp. 195- 196) thatRlippell found M agillls in the Red Sea onlyin a coral closely related to "Maeandrina phry­gia" [M adrepora phrygia Ellis and Solander] ,the type species of Leptoria. All these coralhosts are in the family Faviidae, but theserecords are too few to make it certain thatM agilllS is host-specific.

There are divergent opinions as to the foodand mode of feeding of coralliop hilids, espe­cially of those living internally in corals. Whileaccepting that the external coralliophilids "feedsuctorially on coral tissues," Morton (1958,p. 95) also believed that M agilils is "evidentlya ciliary feeder." Gerlach has extended thisidea to Leptoconcbus (Gerlach, 1960, p. 360,fig. 4, as "Leptoconcba" [wrongly reidentifiedin the 1961 translation as a Magilopsis ]),classifying this as a suspension feeder takingzooplankton. The se ideas can be traced back toYonge ( 1932, p. 274) , who stated of a pre­served M agillls:

It proved impossible to determine the mode offeed ing. Radula and jaws are absent, but there isno certain ind ication of a ciliary feedin g mechanism.Examin ation of the living animal might reveal this .N o sign of a style-sac or a gastric shield was foundin the alimentary canal (n ot very well preserved),and th is indicates that the animal is pro bably not aciliary feeder. As shown later, all the Gastropodaknown to feed by ciliary currents possess sty les. I tis possible that the animal may possess a suckingpharynx and feed on the tissues of the coral, or takezooplankton seized by the tent acles of the po lyps. Astudy of the feeding and other habits of M agi/usand of the other members of the family Cora lliophi li­dae wou ld be of the grea test interest.

There is still no direct information on the food

and feeding of the three genera living in­ternally in corals. In their excellen t study ofthe anatomy and mode of life of Magilopsisand Leptoconcbns, Gohar and Soliman (1963,pp. 106, 108) did not observe feedi ng, coulddetect neither animal nor plant remains in thegut, but concluded that these species "areprobably not ciliary feeders."

In the best study published to date on thefeedin g of any prosobranch symbiotic withcorals, W ard ( 1965) concluded that the salivaof Corallioph ila abbreviata aids in penetrationof the coral epidermis, and that the muscularproboscis is used as a pump to ingest the zo­oxanthellae-containing soft tissues. Earlier , De­mond ( 1957, p. 315) had hinted that C.violacea is nutrit ionally dependent on livingcorals, and Keen ( 1958, p. 370) had statedexplicitly that QlIoYllla madreporarum feedsupon corals.

In view of the anatomical uniformity ofcoralliophilids and in the absence of any director anatomical evidence of ciliary feeding, I be­lieve that they all feed suctorially on theirhosts and the mucus thereon. Even the externalcoralliop hilids are stationary and have a limitednumb er of polyps within reach of their pro­boscises. Coralliophilid proboscises are greatlyextensible, and the hosts show little or no signof injury other than for the substrate scars andburrows. Coralliophilids thus would seem welladapted parasite s, injuring their hosts butslightly. (Ward believes, however, that Coral­liophila abbreviata contr ibutes to the destruc­tion of M ontastrea annularis at Barbados.)

In all coralliophilids, the sexes are separateand the males have a penis. According toGohar and Soliman ( 1963, p. 112 ) , fert iliza­tion in M agilopsis and Leptoconcbus is internal,and (peculiarly) the "spermatozoa are shed inthe surrou nding water and gain access to thefemale with the ingoing current." Th e un­attached, saccate egg capsules of coralliophil idsare unique among prosobranchs in being re­tained in or near the mantle cavity. So far asis known, the veligers are all planktotrophic.Th e only information on settlement is Goharand Soliman's tantalizin g observation ( 1963, p.123) that Leptoconcbus and M agilopsis vel­igers, set free on the surface of a living coral,"remained in their position for some days un-

50

affected, although directly lying on the flour­ishing coral polyps. Th e coral did not kill nordevour the larvae. . . . Th e polyps tended toclose the mouth open ings when the larvae camenearby."

DISCUSSION AND CONCLUSIONS

The living tissues of both hermatypic andaherma typic stony corals are subject to preda­tion and parasitism by a surprising variety ofanimals, including bony and cartilaginousfishes, asteroids, crustaceans, polychaetes, andgastropods. Most of these are facultative pred­ators, but some of the crustaceans and gas­tropods consistently live with and feed on themucus and living tissues of their hosts. Thesesymbionts are all shallow-water, tropical spe­cies; many are Indo-Pacific in distribution.Th ere are preferences for suitably shaped coralhosts and for particul ar genera or families, butoutright host-specificity is uncommon. Oth erpossible predators and parasit es of corals in­clude turtl es, echinoids, pycnogonids, and pro­tozoans.

Among prosobranch gastropo ds, a few spe­cies in the Architectonicidae, Epitoniidae, Ovu­lidae, Muri cidae, and Coralliophilidae areknown definitely to feed on corals, and byextrapolation most other species in these fam­ilies living with corals can be assumed to doso. Among opisthobranch gastropo ds, a feweolids are coral symbionts (notably the tergi­pedid genus Phestilla); there is also a doubtfulreport of one doridoid nudib ranch (PhyllidiabOl/rgini) feeding on corals. These gastropodsrange from foraging predators that crawl inquest of their coral pr ey to sedentary or sessilesyrnbionts with corals-notably the coralli­ophilids, which feed parasitically on coralpolyps without seriously injuring them.

Coelenterate-feeding gastropods show a va­riety of structural modifications of the radulaand of the anterior end of the gut. Ovulidsand some architectonicids have taenioglossateradulae that are little changed , but other archi­tectonicids, epitoniids, and janthinids haveradular teeth each usually with a hooked and1- to 3-pointed distal end. Drnpella has astenoglossan radula with remarkably elongatelateral teeth , likewise hooked distally. Both

PACIFIC SCIENCE, Vol. 24, January 1970

coralliophilids and phyllidiids lack radulae andjaws, and feed suctorially. Both architectonicidsand epitoniids have an elongate, invaginableproboscis and a cuticularized esophagus whichmay prevent injury from nematocysts (Robert­son, 1970) . The proboscis of D rupella (Murici­dae) is cuticularized exteriorly.

Otter believed (19 37, p. 348) that a "layerof living [coral] polyps catches and devoursas food all free-swimming larvae . . . whichhappen to come near them." It has beenclaimed that this is wrong in the case of

.veligers of the two coralliophilid genera thatbore into corals; these larval and postlarvalgastropods are said not to be eaten, and neitherdo they kill the polyps while beginning to boreand to feed. Philippia postlarvae, on the otherhand, have no immunity to predation by corals(Robertson, Scheltema and Adams, 1970).

ACKNOWLEDGM ENTS

This work was supported by N ational ScienceFound ation Grant GB-7008. I thank Dr. JohnS. Garth (A llan Hancock Found ation , LosAnge les, California) and Dr. James C. Tyler(Academy of Natural Sciences of Phil adelphi a)for help with literatur e on crustaceans andfishes, respectively. I also thank Mr. Peter V.Fankboner (University of Victoria, BritishColumbia) , Mr. Larry G. H arris (Universityof California, Berkeley) , and Dr. E. AlisonKay (University of Hawaii) for unpublishedinformat ion.

ADDENDUM (ADDED IN PRESS)

A tenth family of fishes definitely includ espredators on stony coral polyps, the Blenniidae(comb tooth blennies) . Nea r Elat, Israel (Gulfof Aqaba) , Cirripectns sp. and M eiacanthm sp.have this habit (t este Dr. Lev Fishelson, Tel­Aviv University, August 1969).

The latest literature on the population ex­plosion of the asteroid A cantbaster planci in­cludes Chesher (1969) and Fischer (1 969).

Although not strictly a predator or parasite,the newly described Indo-Pacific mytilid bi­valve Fl/ngiacava eilatensis Soot-Ryen ( inGoreau et al., 1969) lives in chemically exca­vated cavities in fungi id corals, and "the long

Predators and Parasites of Stony Corals-RoBERTSON 51

siphons open into the coelenteron where food,consisting probably to a significant extent ofsymbiotic zooxanthellae discharged from thetissues of the coral, is collected."

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