BULLETIN OF MARINE SCIENCE, 47(1): 182-191, 1990

DISTRIBUTION OF INDO-PACIFIC MYZOSTOMA AND HOST SPECIFICITY OF COMA TULID-ASSOCIATED

Mark J. Grygier

ABSTRACT About 113 of Myzostoma. induding at least 26 undescribed ones, are recorded from the non-austral parts of the Pacific and Indian Oceans. Most of these are Pacific; only seven species are Indian Ocean endemics and 12 occur in both oceans. Three Indo-Pacific species also confidently occur in the Atlantic. The most diverse collections have been made in the Philippines (30 species), Japan (27), the Moluccas (26), Queensland (20), and the N orthem Territory (17). The distribution of some species-groups and of 21 relatively well- sampled species is analysed. Some North Pacific species are amphiboreal or have amphiboreal affinities. The species assemblages in Japan, Micronesia, and the Northern Territory overlap comparatively little with the widespread Indo-West Pacific fauna of the Indian Ocean, Phil- ippines, Moluccas, Queensland, and Fiji. Worldwide, 136 comatulid species are known to be myzostome hosts (70 new records), but taxonomically they are not distributed evenly. The Comasterida, Mariametrida, and some subfamilies of the Antedonidae are the most prone to infestation. Usually one to three but up to seven myzostome species infest a given comatulid species. Some well-sampled myzostomes are host-specific at the species, , or family level, but others have up to 10 taxonomically diverse hosts. Therefore, myzostomes may be only partly reliable biological tags for populations.

The Myzostomida are obligate commensals or parasites of echinoderms, par- ticularly of . Their usual textbook status as a class of or an aberrant group ofpolychaetes is by no means a consensus among zoologists (e.g., Jagersten, 1940b). Most species are known from single or very few finds, so, apart from occasional regional faunal lists, there has been little biogeographical analysis ofmyzostomes since Graft's (1884) monograph. Wagin (1970) briefly commented on this subject and its connection with myzostome phylogeny, based on just a few species. My recent study of a large quantity of previously un worked myzo- stome material has increased the number of biogeographically useful species, es- pecially in the Indo-Pacific. A more precise estimate of the extent of host specificity among myzostomes is also now possible.

METHODS

The geographical and host distributions of previously studied myzostomes were compiled from the literature; comatulid host names are as given by Clark (1921) except when modified by the revisions of Rowe et al. (1986) and Hoggett and Rowe (1986). Types of about 60, mostly Indo-Pacific species of Myzostomida were examined. Unidentified myzostomes totalling over 300 lots were examined from worm and crinoid collections at the National Museum of Natural History (Smithsonian Insti- tution), the Smithsonian Oceanographic Sorting Center, the Allan Hancock Foundation, the Zoological Museum in Copenhagen, the Swedish Museum of Natural History, the Uppsala University Zoological Museum, the British Museum (Natural History), the Naturhistorisches Museum Wien, the Australian Museum, the South Australian Museum, and the Northern Territory Museum of Arts and Sciences. Additional, unworked material remains at many of these museums as well as at the Queensland Museum and the Western Australian Museum; the hosts have been noted in these cases, but unex- amined myzostomes are not included in the biogeographical analysis. Since myzostomes were most often found loose in jars with crinoids, host identities must be regarded as circumstantial, not proven. The following sets ofIndo-Pacific species of Myzostoma are considered synonyms (Grygier, in prep.): M. fissum, striatum; M. furcatum, adhaerens; M. wyvillethomsoni, circinatum; M. echinus, pottsi.

182 GRYGlER: DISTRIBUTION AND HOST SPECIFICITY OF MYZOSTOMIDA 183 insigne. probably labiatum; M. wheeleri, terminale. The austral regions of the Indian and Pacific Oceans are not considered in this study, and the Indonesian seas and the Arafura and Timor Seas are treated as Pacific.

BIOGEOGRAPHICAL RESULTS Regional Species Diversity. - Up until now, 88 species of Myzostoma (synonyms excluded) have been described from the Indo-Pacific. I have rediscovered 39 of these and found at least 26 undescribed species in this region; the status of 9 other forms is unclear, although they are treated as separate species here. Thus, to date there are about 113 Indo-Pacific species known, and more are present in the unworked material. In the Indian Ocean, which has not been extensively sampled, seven species are endemic: M. costatum, rubrofasciatum. costatum sensu Boulenger (1913), moebianum, gopalai, gardineri, an undescribed species. Five of these represent single finds. Myzostoma excisum, supposedly from the Caribbean and Indian Ocean, is most likely based on damaged individuals of two species whose identities are unclear. Twelve species occur in both the Indian and Pacific Oceans: M.jissum, lobatum, echinus, plicatum, crosslandi, bocki, furcatum, chelonium, attenuatum, willemoe- sU,two undescribed species (details for most of these given in Table 1).Myzostoma willemoesii is found in the Atlantic as well. The identity of M. carinatum, also recorded from all three oceans and one of the troublesome costatum-group (see below), must be considered questionable. Myzostoma jissum, lobatum, attenu- atum, crosslandi, and willemoesii have very broad east-west distributions (Table 1), but M. echinus, bocki, and new species 10 only range westward to the Indian Ocean coast of Australia. The remaining species are Pacific endemics except for M. gigas and M. ingolfi, which are principally known from the North Atlantic. Pacific regions that have been extensively sampled for myzostomes usually show a high diversity (Fig. 1). The Philippines, especially Bohol and the Sulu Archipelago, have 30 species. Japan, especially east-central Honshu and the Goto Islands, has 27, and the Moluccas, especially Aru and the Kei Islands, have 26. Queensland, especially the Torres Straits and Lizard Island, has 20 species, and the Northern Territory 17.Fiji and vicinity have yielded 9 species, and Micronesia (namely Belau, Saipan, Truk, and Enewetak) 8. There has obviously been undersampling in China and Indo-China (6 species), the remainder of the Indo-Malayan Archipelago and Malay Peninsula (5), and Polynesia (5). None have been recorded from Hawaii, French Polynesia, or New Zealand. Low diversity along the South and Central American coasts (no species) and the west coast of North America (3) is probably due to the very low crinoid diversity there. Distribution of Species-Groups. - Myzostoma is a large, heterogeneous genus. This is not the place to divide it formally, but it is possible to discuss the distribution of some recognizable species-groups. The crosslandi-group includes species with moderately to very elongate bodies that have a dentate or scalloped margin instead of the usual 10 pairs of marginal cirri, and with the lateral organs very close to the margin; some have transverse ridges. This group includes M. crosslandi, nanseni, sulcatum, elongatum, folium, taeniatum, membranaceum,fasciatum, maculatum, possibly a few other described species, and several undescribed ones. It is strictly Indo-West Pacific, occurring in the Red Sea, Kyushu, Hong Kong, the Philippines, the northern and southern Moluccas, the Northern Territory, the Great Barrier Reef, and Fiji. 184 BULLETIN OF MARINE SCIENCE, VOL. 47, NO. I, 1990

Table 1. Indo-West Pacific species of Myzostoma known from at least three collections or from two widely separated locales, with collection localities, based on literature and own data

Species Collection localities elongatum Philippines: Bohol, Manila Bay; SW of Fiji elegans Bohol; Banda Ids.; Fiji longimanum Japan: Goto Ids., Vraga Strait, Sagami Bay, off Ose Zaki (Honshu) polycyc!us Philippines: J010, Mindoro; Torres Straits; SW of Fiji willemoesii Philippines between Negros and Siquijor; Arafura Sea; Kei Ids.; SW of Fiji; Ker- madec Ids.; Cape of Good Hope; off East London, South Africa; Bahamas: Great Bahama Bank, Great Abaco chelonoidium Japan: Sagami Bay, Vraga Channel, offOmai Zaki (Honshu); Flores Sea chelonium Sagami Bay; Andaman Sea longicirrum Philippines: Gulf of Davao, Zamboanga, near Siasi, Jolo; Singapore furcatum Madras; Moluccas; Kei Ids.; Solomon Ids.; Philippines: Visayan Sea, E Sulade Is.; Lizard Is. bocki Japan: Sagami Bay, Misaki; Hong Kong; between Fremantle and Geraldton, Western Australia crosslandi Red Sea: VI Shubuk, near Eilat, Ras Buska (Sinai); E of Halmahera; Fiji echinus (s.l.) Holothuria Bank, NW Australia; Japan; Formosa Straight; NE tip of Sulawesi; Torres Straits; Lizard Is.; Viti Levu, Fiji; SW of Fiji coriaceum N of Jolo; Moluccas; Kei Ids.; Lizard Is.; Fort Denison, Queensland ambiguum Bohol; Moluccas; Marsegoe Is. offCeram; Great Banda Is.; Lizard Is.; Fiji; Enewetak attenuatum northern Bay of Bengal; Andaman Sea off Phuket, Thailand; Maldives; Singa- pore; Malaysia; Ta Bui Is., Indonesia; Cootamundra Shoal, Timor Sea; Lizard Is. lobatum Bohol; Eilat, Israel fissum Zanzibar; Bombay; Travancore State, India (now part of Kerala); Madras; Red Sea (near Eilat); Western Australia: Houtmann Abrolhos Ids., Cape Boileau; Northern Territory: several localities; Cauda Nhatrang, Vietnam; SW of Fiji; Palau sp. 10, n. sp.? near Siasi, Sulu Archipelago; Port Essington, Northern Territory; Murion Is., Ex- mouth, Western Australia sp. 31, n. sp. Gulf of Davao; Queensland: Lizard Is., Heron Is. sp. 47, n. sp. off Hong Kong; Sulu Sea; Amboina, Indonesia sp. 83, n. sp. Lizard Is.; Fiji; Koror, Palau

The platypus-group, consisting of M. platypus, aruense, ijimai, and probably an undescribed species, is distinguished by ventral processes and very broad, flat parapodial bases and lateral organs, and by the habit of living in cysts or in the mouth of the host crinoid. This is also an Indo-Pacific group found in the Red Sea and in the Pacific as far north and east as Japan, Enewetak, and the Great Barrier Reef. The costatum-group includes flat-bodied, round or oval species with a radiating pattern of dorsal ridges that extend outwards as marginal teeth. This group is in need of revision, but I include in it M. costatum, p!icatum, cristatum, carinatum, and rubrofasciatum sensu Boulenger (1913). This assemblage occurs throughout the Indian Ocean and east to the Moluccas and Torres Straits (plus supposedly M. carinatum in the Caribbean). Myzostoma costatum sensu Boulenger (1913), distinguished by its short caudal processes and 6 pairs oflateral organs, is restricted to the Red Sea. Dorsa.lly costate species that have larger caudal processes, like M. fissum and M. furcatum, occur in the Indian Ocean, too, M. fissum very widely, but they also extend well into the Pacific, to Fiji and the Solomon Islands, re- spectively (Table 1). Dome-shaped, dorsally costate specimens, which I believe all belong to M. echinus, are widespread in the Pacific, but are also found in GRYGIER: DISTRIBUTION AND HOST SPECIFICITY OF MYZOSTOMIDA 185

NORTH PACIFIC (4)

(0) ... (27) ...... • • e ••

(0)

INDIAN OCEAN

(19) , ......

Figure 1. Distribution of species of Myzostoma in the Indo-West Pacific based on literature records and new information. The geographical regions discussed in the text are outlined, the num ber of species found until now in each region is enclosed in parentheses, and the nine black squares indicate sites of particularly heavy collecting.

Western Australia (Table 1). The dorsally costate species seem to show an ill- defined transition in dominant body morphology from west to east. The ambiguum-group has species with flat, round to shield-shaped bodies and the anterior and posterior one to two pairs of marginal cirri much longer than the others: M. ambiguum, antennatum, longimanum, vastum, longicirrum. and a Japanese species that has been referred to as M. antennatum by McClendon (1906) and asM. ambiguum by Jagersten (1937) and Kato (1952). All these species 186 BULLETIN OF MARINE SCIENCE, VOL. 47, NO.1, 1990

Table 2. Number of pair-wise species range overlaps among eight geographical regions defined in Figure I for the 21 species of lVfyzostoma listed in Table I

Region 10 Ph Mo NT Q Mi F Totals Japan (J) 3 0 1 0 1 0 I 6 Indian Ocean (10) 3 5 4 3 4 I 4 24 Philippines (Ph) 0 5 6 2 6 I 5 25 Moluccas (Mo) 1 4 6 0 5 I 5 22 Northern Territory (ND 0 3 2 0 1 1 1 8 Queensland (Q) 1 4 6 5 2 5 24 Micronesia (Mi) 0 I 1 1 2 3 9 Fiji (F) 1 4 5 5 5 3 24 are Pacific except for the type specimens of M. vastum from the Caribbean (their relationship to the better described Pacific specimens of that species (Graff, 1884) is unclear). Myzostoma ambiguum per se is tropical, its range including Bohol, the Moluccas, the Great Barrier Reef, Enewetak, and Fiji, based entirely on new material. The wyvillethomsoni-group, the last to be considered, includes species with long, oval bodies and prominent parapodial cirri, the first three pairs directed anteromedially, the last two pairs posteromedially. Myzostoma wyvillethomsoni, wheeleri, and cirripedium infest metacrinine stalked crinoids in the Philippine- Moluccan region and in Japan. In southern California, M. ingolfi infests an ophiu- roid (Allan Hancock Foundation material), while its host in the North Atlantic is evidently also an ophiuroid (see Mortensen, 1933: 24 and Jagersten, 1940a: 114). The east-west host group distinction in this species-group is remarkable. Myzostoma Faunal Provinces. -Four North Pacific species have amphiboreal affinities. Myzostoma gigas, reported from Korea and the Sea ofJ apan, is otherwise most widely known from the far North Atlantic (Sturn mer- Traunfels, 1910). My- zostoma pseudogigas from British Columbia and Southern California is closely related to M. gigas (Jagersten, 1940a), but similar tropical Pacific species like M. coriaceum also exist. Myzostoma deani from California, Washington, and Japan is very similar to the North Atlantic M. carpenteri, differing in the dorsal surface texture. Finally, M. ingolfi was discussed above. Do all the remaining species constitute an Indo-West Pacific Myzostoma as- semblage, or are there further subdivisions? This depends on the degree of range coincidence of all the species involved. Unfortunately, most are only known from one or two records, but 21 well-delineated species are either known from three or more distinct records or from two widely separated localities (Table 1). Most localities for each of these species could be assigned to either the Indian Ocean, Japan, Philippines, Moluccas, Northern Territory, Queensland, Micronesia, or Fiji (for boundaries see Fig. 1). Three species, M. longimanum, longicirrum, and chelonoidium, are found only in a single one of these regions. For each region, it is possible to determine how many of the remaining 18 species it shares with each of the other six regions (Table 2). Japan, the Northern Territory, and Micronesia are relatively isolated, judging from their low level of bilateral species sharing (6- 9, versus 22-25 for the other regions). However, a widespread Indo-West Pacific myzostome fauna is indicated by the uniformly high (5-6) pairwise values between all pairs of the Philippines, Moluccas, Queensland, and Fiji, and the slightly lower values (usually 4) between the Indian Ocean and these regions. The apparent provinciality of Japan's myzostome fauna is partly due to several non-Japanese localities for its species falling outside the considered regions (e.g., GRYGIER: DISTRIBUTION AND HOST SPECIFICITY OF MYZOSTOMIDA 187

M. bocki in Hong Kong, M. chelonoidium in the Flores Sea), but it is also likely that geographical and climatic conditions allow only a subset of the mostly tropical species under consideration to thrive there. A study now in progress on Okinawan myzostomes may clarify the nature of this faunal boundary. The low value for Micronesia might be an artifact of the low number of species recorded from there, but Fiji has about the same number of species and a much higher faunal overlap involving every one of the species so far known from there. Fiji clearly belongs to the major Indo-West Pacific province while Micronesia probably does not. The isolation of the Northern Territory's myzostome fauna is surprising, there being only M. attenuatum in common with Queensland, for example. It will be inter- esting to see how the unworked specimens in the Western Australian Museum will compare with the Northern Territory on the one hand, and the Moluccas, Queensland, and previous Indian Ocean records on the other.

HOST SPECIFICITY OF MYZOSTOMES INHABITING COMATULIDS Host Range. - The majority orIndo-Pacific species of Myzostoma infest crinoids. Just four occur on ophiuroids: M. japonicum, ingolfi, holotuberculatum, and an undescribed species. Only comatulid crinoid hosts will be considered here; my- zostomes associated with them belong to the genera Myzostoma, Cystimyzosto- mum, and Mesomyzostoma. Species of Myzostoma, Cystimyzostomum, and Ste- lechopus do occur on stalked crinoids, but the lack of a contemporary checklist of the world's stalked crinoids has prevented their consideration here. The hosts of many myzostomes are not indicated or are questionable in the literature; the following 66 species of comatulids can be considered as positively implicated, and another seven species, not listed, may be regarded as questionable hosts. In this list, species names have been brought up to date, and the number of myzo- stome species recorded from each, including those from my study, is given (syn- onyms taken into account). A "+" indicates that there is unstudied material from this host that may include one or more additional species. Comatel/a nigra (5), stelligera (2); Neocomatel/a pulchel/a (3); Capillaster mul- tiradiata (4 +); Davidaster rubiginosa (2), discoidea (2); Comatula solaris (2), pectinata (4); Comactinia echinoptera (7), meridionalis (4); Comanthus briareus (3+), delicata (l),parvicirrus (10+); Comanthina nobilis (I); Oxycomanthuspin- guis (2), exilis (2),japonica (3 +); Zygometra microdiscus (3 +), elegans (3); Hime- rometra robustipinna (2); Heterometra savignyi (3), crenulata (4), variipinna (1), ater (2); Amphimetra mol/eri (2), tessel/ata (6 +); Stephanometra echinus (1 +), oxyacantha (3 +),spicata (I +);Lamprometra palmata (6), klunzingeri (3); Analci- dometra armata (3); Colobometra perspinosa (3); Cyllometra manca (2 +); De- cametra chadwicki (5 +); Oligo metra serripinna (3 +); Tropiometra afra (3 +), carinata (2 +); Pectinometraj!avopurpurea (1 +); Parametra orion (1); Stiremetra breviradia (I); Haraeometra duplex (1); Monachometra j!exilis (2); Glyptometra inaequalis (2), tuberosa (2 +),angusticalyx (1); Crinometra brevipinna (3); Charito- metra basicurva (2), incisa (2); Dorometra parvicirra (1); Antedon bifuia (1 +), petasus (2), mediterranea (2), adriatica (2); Florometra serratissima (2), asperrima (1); Cocco metra hagenii (3); Heliometra glacialis (2+); Promachocrinus kergue- lensis (3); Anthometra adriani (2); Adelometra angustiradia (2); Leptometra pha- langium (2), celtica (2); Poliometra prolixa (3 +); Hathrometra sarsii (I); Thau- matometra parva (I). The present study has produced new myzostome material from 43 of these species. The following 70 comatulid species represent new hosts for myzostomes, mostly from my study, but a few first recorded in an unpublished Japanese Master's 188 BULLETIN OF MARINE SCIENCE, VOL. 47, NO. I, 1990 thesis (Tamura, 1983; his records indicated by "*"). A "+" again indicates that some or all of the material from this species is unstudied; usually only one my- zostome species is involved. Comanthus bennetti and Zygometra comata represent confirmations of these species' earlier status as suspected hosts. Comatella maculata (+); Capillaster sentosa* (3 +); Nemaster grandis (3); Co- missia parvula (1); Comatula purpurea (2); Comaster multijida (3 +),gracilis (1), multibrachiata (1 +), distinctus (+); Comanthus alternans (1), suavia (+), wahl- bergi (2+), mirabilis (-+-), gisleni (1); Comanthina schlegelii (6+), variabilis (+); Cenolia trichoptera (1), benhami (+), glebosum (+); Clarkcomanthus albinotus (1), littoralis (1), luteojuscum (2); Oxycomanthus perplexus (1), bennetti* (4 +), grandicalyx (1), comanthipinna (1); Zygometra comata (2); Catoptometra mag- nifica (+); Himerometra magnipinna (2), bartschi (1); Heterometra affinis (+), bengalensis (+), africana (1), flora (1); Oxymetra erinacea (1 + ), jinschi (1); Ste- phanometra spinipinna (+), indica (2 +); Liparometra articulata (1 +); Dichro- metra flagellata (3); Mariametra subcarinata (+); Pontiometra andersoni (3); Cenometra bella (1), corn uta (1); Oligometrides adeonae (1); Petasometra helian- thoides (1); Decametra mylilta (+); Oligometra carpenteri (1); Tropiometra mag- nifica (-+-); Neometra spinosissima (1), multicolor (4 -+-); Pectinometra magnifica (1); Pterometra venusta* (+), pulcherrima (1); Crotalometra magnicirra (1); Mo- nachometra patula (+); Glyptometra crassa (+), distincta (1), macilenta (1), sc/a- teri (1), levigata (+); Notoerinus mortenseni (1); Argyrometra mortenseni (1); Euantedon polytes (+); Antedon duebeni (1); Florometra mariae (1), mawsoni (1); Hypalometra defecta (+); Psathyrometra mira (+); Isometraflavescens (1). In all, about one quarter of the known species of comatulids have been shown to host myzostomes. However, different comatulid taxa are unequally subject to myzostome infestation. In the superfamilies Comasterida and Mariametrida, and the combined antedonid subfamilies Antedoninae and Heliometrinae, the pro- portion of known host species is, respectively, 44% of 101 species, 30% of 139, and 26% of 57. The same values in the superfamily Tropiometrida and the re- mainder of the Antedoniidae are 20% of 125 species and 10% of98, respectively. The percentage for the Tropiometrida would be lower except for 8 of the 15 species of Glyptometra being infested, most often with gallicolous Myzostoma willemoesii or Cystimyzostomum. Many morphological and ecological characteristics of different crinoids might be involved in this pattern of host preference, but they have not been evaluated yet. Among these are size, morphological complexity, depth range, geographical distribution, dominance in the community, food selection, other aspects of be- havior, toxic properties, and other symbionts. The observed pattern may also be partly artificial, reflecting the relative abundances of crinoid taxa in museum collections and the confused state of crinoid . Crinoid type specimens were purposely excluded from the survey for myzostomes, so there is a bias against rare species being listed as hosts, and Clark and Rowe (1971) suggest that there are many synonymous species in some mariametridan genera. Moreover, without a cladistic treatment to assure the monophyly of the mentioned crinoid higher taxa, there is no assurance that they are meaningful in the present context.

Host Specificity. -A plurality of the previously known comatulid host species bears 2 myzostome species (26 crinoids), 15 species bear 1 myzostome while 15 more bear 3, and 10 comatulids have 4 or more species ofmyzostome symbionts. In contrast, the majority of the newly recorded host species have just one my- zostome species, or else their myzostomes remain unstudied. Some of these new hosts will probably prove to bear additional species, but for now only three of GRYGlER: DISTRIBUTION AND HOST SPECIFICITY OF MYZOSTOMIDA 189

Table 3. Number of host comatulid crinoid species recorded for Indo-West Pacific species of My- zosloma that have been taken from identified hosts on at least three occasions

Myzostoma species Number of host species (genera or families)

longimanum I bocki I nanseni I sp. 4, n. sp. I deani 2 (1 genus) coriaceum 2 (2 families) elongatum 2 (2 families) sp. 83, n. sp. 2 (2 families) sp. 47, n. sp. 2 (2 families) elegans 3 (1 family, Comasteridae) sp. la, n. sp.? 3 (1 family, Comasteridae) chelonoidium 3 (I family, Calometridae) chelonium 3 (2 families) sp. 31, n. sp. 4 (I family, Comasteridae) longicirrum 4 (2 families) Jurcatum 5 (2 families) crosslandi 5 (3 families) fissum 7 (3 families) willemoesii 8 (2 families)· ambiguum 8 (4 families) altenuatum 10 (3 families) • Includes I western Atlantic host. them are confirmed to host four or more myzostome species. The maximum reliable number for any comatulid appears to be seven myzostome species in- habiting Comactinia echinoptera in the western Atlantic. Comanthus parvicirrus. with lO recorded myzostomes (I have found just 3) has had a complicated taxo- nomic history; some myzostomes recorded from it are probably from other cri- noids, and there would have been 12 associated species had not Rowe et al. (1986) separated Oxycomanthus exi/is from C. parvicirrus. Of the 13 comatulids with 4 or more myzostome species, 2 are western Atlantic and the rest Indo-West Pacific. Of the latter, six are comasterids: Comatella nigra, Capillaster multiradiata, Co- matula pectinata. Comanthus parvicirrus, Comanthina schlegelii. and Oxycom- anthus bennetti. The remaining heavily infested species belong to various families: Heterometra crenulata and Amphimetra tessel/ata (Himerometridae), Lampro- metra palmata (Mariametridae), Decametra chadwicki (Colobometridae), and Neometra multicolor (Tropiometridae). Thus, not only is the Comasterida the most universally infested crinoid taxon, but it also has the largest number of species supporting diverse myzostome faunas. From a biogeographical point of view, a symbiont species' host specificity is more important than the number of species a host bears. Strict host specificity would make symbiont distribution a function of host distribution modified by ecological factors and vicariance. Lack of host specificity means that a symbiont's distribution is mostly independent of an individual host species' distribution and biogeographical history. It is worthwhile to ask whether myzostomes can serve as biological tags for comatulid crinoids. Twenty-one Indo-Pacific myzostome species have been collected often enough (arbitrarily defined as more than three times with the host identified) to make a judgement about their degree of host specificity (Table 3). Considering positively identified hosts only, strict host specificity is exhibited by Myzostoma bocki (on Tropiometra aJra), M. nanseni (on Stephanometra indica), and M. longimanum 190 BULLETIN OF MARINE SCIENCE, VOL. 47, NO.1, 1990

(on Oxycomanthus pinguis). Among species with multiple hosts, higher level specificity may be evident. Myzostoma deani lives on two species of Florometra. Family level specificity is shown by M. chelonoidium on three species of Calo- metridae (Neometra multicolor, Pectinometra jlavopurpurea, P. magnifica) and by M. willemoesii on seven species ofCharitometridae (4 species of Glyptometra, Crinometra brevipinna, Charitometra basicurva, Monachometrajlexilis), although the latter also occurs on the thalassometrid Crotalometra magnicirra. Three species seem to show no host specificity. Myzostoma fissum has been found on seven species, five of them mariametrids, but also a comasterid and a heterometrid. I have found M, ambiguum on eight species in four families (4 of them comasterids, 2 mariametrids, a colobometrid, and a himerometrid) in two suborders. The greatest variety of host species is utilized by M. attenuatum (Grygier, 1989): the comasterids Capillaster sentosa, Comaster multifida, Comaster gracilis, the mariametrids Stephanometra oxyacantha, Oxymetrafinschi, and the colobomet- rids Colobometra perspinosa, Pontiometra andersoni, Decametra mylitta, Ceno- metra corn uta, and Petasometra helianthoides. The quite different expressions of host specificity exhibited by various myzo- stomes make care necessary in choosing appropriate species for biogeographically oriented coevolutionary studies of crinoids and their attendant myzostomes.

ACKNOWLEDGMENTS

I would like to thank collectiively the curators of marine invertebrates, worms, and echinoderms at the museums listed in the Methods section for providing access to type specimens, unworked my- zostome collections, and crinoid collections. I would especially like to thank Dr. K. Fauchald for his encouragement in taking up a study of the Myzostomida. This work was conducted while I held a Smithsonian Institution Postdoctoral Fellowship and was prepared for publication during a stay as Visiting Foreign Researcher at the Sesoko Marine Science Center, University of the Ryukyus, Dr. K. Yamazato director.

LITERATURE CITED

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genera from Australia (Echinodermata: Crinoidea), with descriptions of two new genera and nine new species. Zool. J. Linn. Soc. 86: 197-277. Stummer-Traunfels, R. R. v. 1910. Arktische Myzostomen. Mit einem Anhang: Ueber den Bau der Borstendriisen bei Myzostoma gigas Graff. Fauna Arctica 5(1): 73-86. Tamura, R. 1983. The shallow water crinoids and their commensal . M.S. Thesis, University of the Ryukyus. 40 pp. (In English) Wagin, V. L. 1970. On the connection of phylogeny and the geographical spreading of animals. Pages 3-22 in V. L. Wagin, ed. Voprosy Evolyutsionnoy Morfologii i Biogeografii [Questions of evo- lutionary morphology and biogeography]. Kazan Univ. Press, Kazan, USSR. (In Russian)

DATEACCEPTED: February 20, 1989.

ADDRESS: Sesoko Marine Science Center, University of the Ryukyus, Sesoko, Motobu-cho, Okinawa 905-02, Japan; PRESENTADDRESS:14804 Notley Road, Silver Spring, Mary/and 20905.