Bijdragen tot de Dierkunde, 53 (2): 218-226 — 1983

A new marine triclad ectoparasitic on Malaysian and

Indonesian horseshoe crabs (Platyhelminthes, ,

Tricladida)

by

Ronald Sluys

Institute of Taxonomie Zoology, University of Amsterdam,

P.O. Box 20125, 1000 HC Amsterdam, The Netherlands

been found Summary or, perhaps, even a fifth species, has

on an American Horseshoe Crab from North A of undata new species marine triclad, Ectoplana n. sp., Carolina (Sluys & Ball, unpublished manu- ectoparasitic on the horseshoe crab Tachypleus gigas, is described. Cocoons of triclads found Kaburaki described the were on T. gigas as script). Ijima & (1916)

well as on the horseshoe crab Carcinoscorpius rotundicauda; marine triclad Procerodes limuli which had been

since from the latter species no triclads were collected, it obtained from specimens of the Chinese remains unknown whether these cocoons are those of E. Horseshoe Crab. One Kaburaki year later, undata The or of another species. Ectoplana, though transferred the the Ec- (1917) species to genus poorly defined, is here retained, for stated reasons, pend- is considered the Pro- ing a revision of the . toplana which to belong to

cerodidae and to constitute the only memberof Résumé the subfamily Ectoplaninae (cf. Bresslau,

Some later Kaburaki On décrit une nouvelle espèce de Triclades marins (Ec- 1933). years (1922) pro- vided detailed of toplana undata n. sp.), ectoparasite du Xyphosoure a more description Ectoplana

Tachypleus gigas. Des cocons de Triclades ont été trouvés limuli.

aussi bien T. le sur sur Xyphosoure Carcinoscor- gigas que In this of triclad is paper a new species n’a trouvé des Triclades pius rotundicauda; puisqu’on pas described, of which the were ob- dernière specimens sur cette espèce, la question de savoir si ces

tained from a of horseshoe crab other cocons ceux de undata bien species sont E. ou d’une autre espèce,

Le than mentioned above. In reste sans réponse. genre Ectoplana est retenu, en dépit the two already du fait qu’il est imparfaitement défini, en attendant une assessing the generic status of this species of révision des Procerodidae; les raisons de cette initiative triclad it will be necessary to examine critically sont expliquées. the defining characters of Ectoplana, as de-

scribed in the literature. cocoons INTRODUCTION which found of another were on specimens still

species of horseshoe crab from Malaysian and Marine triclads are known to live ec- Indonesian regions will also be described. toparasitically on the American Horseshoe

Crab Limulus polyphemus (Linnaeus, 1758) and the Chinese Horseshoe Crab Tachypleus triden- MATERIAL AND METHODS tatus (Leach, 1819). These live on the gills and legs of the crabs and profit from the The Zoological Museum in Amsterdam (ZMA)

left houses small alcohol collection of food particles over from the meals of the lat- a horseshoe ter. crabs in which three species are represented,

From L. polyphemus no less than four species viz. Limulus polyphemus, Carcinoscorpius rotun- of triclads have been described (cf. Wilhelmi, dicauda (Latreille, 1817), and Tachypleus gigas

1909). All these belong to the family (Müller, 1785). Specimens of the last two

which contains searched for marine triclads , also free-living species were and/or members. A different form of Bdelloura Candida their cocoons. These horseshoe crabs were BIJDRAGEN TOT DE DIERKUNDE, 53 (2) - 1983 219

either collected and preserved immediately, or Etymology. — The specific epithet undata (from

the of Artis Zoo in shipped to Aquarium the Latin unda, wave) refers to the wavy course

Amsterdam (NAM), where they lived for of the distal portion of the male atrium.

several years before they died and were

the collection of the External features — deposited in museum. (fig. 1). The holotype

crab from which measured about 2.5 in and 1.25 Horseshoe specimens cocoons mm length mm

and/or planarians were collected, are listed in diameter. The body is elongate-oval-shaped,

collec- rounded. The below with their sample locality, date of whereas front and hind end are

and collector. small lie considerable distance from tion, eyes at a

the front end and close Both are together. ZMA Xi. 1007, Tachypleus gigas (mistakenly identified as paratypes were very much shrunken, due to Carcinoscorpius rotundicauda), Singapore, date ofcollection contraction, and of semi-circular shape. The unknown, died in Aquarium NAM 7.09.1965: one due lack of triclad and cocoons. are white, to pigment;

T. ZMA no collection number, gigas. Belawan, Deli, ovaries, testicular follicles, intestinal rami, part

died in Sumatra, 1931, leg. Capt. G.J. Terwiel, aqua- ventral of the copulatory apparatus and nerve

rium at unknown date: two triclads and cocoons. visible the wall. cords are through body ZMA no collection number, T. gigas, Belawan, Deli,

Sumatra, 1931, leg. Capt. G.J. Terwiel, died in Aqua-

rium NAM unknown date: and dermal musculature.— Dorsal at cocoons. Epidermis

ZMA ibid.: cocoons and ventral epithelium measure about 4.8 /tm ibid.: ZMA cocoons in thickness; both are packed with rhabdites. ZMA Xi.1004, 2 specimens of T. gigas, Java Sea, 1925, Ventral and dorsal body surface are covered leg. Capt. G. J. Terwiel: cocoons. which with numerous, cilia have ZMA Xi.1002, T. gigas, Java Sea at Pekalongan, Java, well-developed the cells. 1927: cocoons. about same height as the epidermal

ZMA Xi. of further 1001, T. gigas, east coast Sumatra, no The basement membrane is well developed and

information: cocoons. conspicuous. Dorsally and ventrally it is about ZMA Xi. 1003, Carcinoscorpius rotundicauda, Sabang, 2.4 /tm in diameter. The dermal musculature is Sumatra, no date of collection, leg. G. Herman: well developed. Immediately beneath the base- cocoons (there is a town Sabang on Celebes as well as

a small N. but Van membrane there is of circular on island of Sumatra, according to ment a layer

Benthem G. Herman stationed Jutting (1939) was on muscles, consisting of two rows of fibres. In-

Sabang, Sumatra). of this there is teriorly layer a layer of ZMA 3 of C. rotundicauda, Xi.1006, specimens , Singapore, muscles which longitudinal measures dorsally died in Aquarium NAM in October 1964: cocoons from about 7.2 in diameter and about the gills of all three crabs. /im ventrally

12 /un.

SYSTEMATIC SECTION

— In the Alimentary system. the holotype

TRICLADIDA between pharynx measures one-fifth and one-

sixth of the It is constructed body-length. as Genus Ectoplana Kaburaki, 1917 follows: outer ciliated epithelium of about 2.4

undata (tm, outer longitudinal muscle layer of 2.5 /im, Ectoplana n. sp. circular muscle of 4.8 outer layer /tm, paren- Holotype: ZMA V.PI.603: sagittal sections on 2 slides, of 49 inner chymatous zone /tm, longitudinal stained in Mallory-Heidenhain; specimen collected from muscle of 4.8 inner circular muscle Tachypleus gigas from Singapore (ZMA Xi.1007). layer /im, of 24 inner ciliated of 2.4 Paratypes: ZMA V.PI.604.1: sagittal sections on 2 slides, layer /im, epithelium

stained in Mallory-Heidenhain; specimen collected from /im. T. gigas from Deli, Sumatra; ZMA V.PI.604.2: sagittal The anterior ramus of the intestine does not sections stained in on 1 slide, Mallory-Heidenhain; extend in front of the but terminates collected eyes, from same specimen of T. gigas as paratype ZMA behind the brain. It off about 6 7 V.PI.604.1. gives or pairs

All sections made intervals of 8 of lateral diverticula. Both rami are were at /im posterior 220 R. SLUYS - TRICLADS ON HORSESHOE CRABS

1. Dorsal view of of undata A: B: ZMA C: Fig. preserved specimens Ectoplana n. sp. holotype, paratype V.Pl.604.1,

paratype ZMA V.Pl.604.2.

confluent at the hind end of the This was the the deferentia into body. bulb, vasa open a large, difficult to observe in the holotype, whereas it rounded seminal vesicle. From the distal sur-

in the vesicle could not be seen paratypes. Com- face of this a narrow ejaculatory duct missures between the rami be which into the blunt of the posterior may arises, opens tip

The mouth situated the The seminal vesicle is lined present. opening is at penis papilla. with a hind end of the pharyngeal pocket. cuboidal, nucleate epithelium and is surround-

ed by a layer of circular muscle fibres.

— The consists of small bulb and Male reproductive system (figs. 2, 3). The penis a a very testicular follicles few in number: about 6-8 and blunt has are short papilla which a disposition

either side of the the The on body. They occur more or more or less parallel to body surface. less in pairs between the intestinal branches (see nature of the lining epithelium of the papilla fig. 1A). In dorsal view the follicles are oval- could not be discerned and neither nuclei nor

whereas in sections muscles A fine shaped, sagittal they appear subepithelial were seen.

The secretion could be discerned in the as semi-circular or oval-shaped bodies. granular follicles and of the but the location of the are large occupy most space papilla, exact glandular between dorsal and ventral body surface. They cells remained obscure. The musculature of the extend from behind the ovaries up to the root of penis bulb is only weakly developed. the pharynx. The penis papilla projects into a rather

In the pharyngeal region the vasa deferentia spacious dorsal portion of the male atrium

form At first which distal enlarge to false seminal vesicles. narrows considerably into a narrow these of the ventral into the This run laterally nerve cords, part that opens common atrium.

distal of the male atrium is but at the level of the mouth opening they turn narrow portion

well and before rather and has less medially as as dorsally narrow long a more or undulated,

In ZMA V.PI.604.1 the penetrating the penis bulb. Just after entering wavy course. paratype BIJDRAGEN TOT DE DIERKUNDE, 53 (2) - 1983 221

2. reconstruction of the ofthe Abbreviations: bc: bs: bur- Fig. Sagittal copulatory apparatus holotype. copulatory bursa,

sal dd: ed: male canal, densely staining dots, ejaculatory duct, ma: atrium, mu: muscle fibres, ov: oviduct, pp: penis

shell seminal vd: papilla, se: secretion, sg: glands, sv: vesicle, vas deferens.

3. reconstruction of the ZMA V.PI.604.1. Abbreviations in 2. Fig. Sagittal copulatory apparatus of paratype as fig.

male atrium shows bend distal of the male atrium shows a very pronounced very part a nar-

whereas in and directed In ZMA (fig. 3), the holotype paratype row, dorsally fold. paratype

ZMA V.PI.604.2 the is much V.PI.604.2 this fold bending was not as conspicuous as smoother. The of this in the other The lining epithelium narrow two type-specimens. male distal of the male atrium shows atrium is surrounded of portion no by a layer circular

of nuclei. In this respect it differs from the prox- muscles, consisting several rows of muscle

of the male atrium with this imal, more spacious, part fibres, entally to layer, a zone of which shows nucleate In the a epithelium. longitudinal mucles, also consisting of several

of holotype and paratype ZMA V.PI.604.1 the rows fibres. The thickness of both layers 222 R. SLUYS - TRICLADS ON HORSESHOE CRABS

the of the diminishes on proximal portion terspersed with longitudinally or irregularly

atrium. fibres. There also fibres running are which from

the bursal canal run into the anterodorsal por-

— The of the canal. Female reproductive system (figs. 2, 3). tion parenchyma surrounding the

ovaries situated paired, oval-shaped are directly Apart from the orange-red staining shell

behind the brain. In the holotype their size is glands, the bursal canal is also surrounded by

decided about 101 72 and in the ZMA blue dots. It could not be x /xm, paratypes deep staining

ZMA 74.5 48 whether dots with the insunk V.PI.604.1 and V.PI.604.2 x these correspond

In of nuclei of the with unicellular /im and 31 x 17 fim, respectively. none epithelium or

the I able discover that into the bursal type-specimens was to a glands open canal, or even

of trace of oviducts in the anterior part the with nuclei of muscle fibres.

unable in body. Therefore, I am to describe

what the oviducts arise from the ovaries. At —The consist way Eye. eyes of a single-celled pig-

the level of the the oviducts bend the number of retinal cells could gonopore ment cup; not

and into the distal be determined with There is lens medially open separately certainty. no

the the the part of the bursal canal. In holotype to eye.

into the distal of the oviducts open very part

bursal close the of the Cocoons — found canal, very to opening (fig. 4). Many cocoons were

canal into the atrium. In the attached the leaves of the crab common paratypes to gill horseshoe

the openings of the oviducts are located specimens from which the type-specimens of Ec-

somewhat before undata collected. intact more dorsally. Shortly open- toplana were An cocoon

into the female the from the crab ing copulatory apparatus, was obtained only on which the

oviducts receive the of shell found. openings glands. holotype was This cocoon was yellowish

The vitellaria are only moderately developed. brown, whereas the ruptured cocoons were

from dorsal ventral They may extend to body brown. The ruptured cocoons from the

and from behind the ovaries horseshoe crab from which the surface, occur up Deli, on

the level of the undata to copulatory apparatus. paratypes of Ectoplana were found,

Thefemale consists of brown coloration. The copulatory apparatus a showed a yellowish

rounded, oval- or sac-shaped bursa and an ob- dimensions of the cocoons may be derived from

oriented bursal canal. The latter arises the liquely figures. The cocoons consist of an egg- from the anterior the and close with short It surface of bursa shaped receptacle a pedicel. was

it shows determine the cir- to this point a small, dorsally directed impossible to exact extension. Hereafter, the bursal canal runs cumference, and thus the size, of the end plate obliquely towards the ventral body surface and to which the pedicel is attached.

into the atrium. The bursa is opens common lined with a nucleated and vacuolated epithelium, consisting of cuboidal cells. It is COCOONS FROM OTHER HORSESHOE surrounded by a layer of muscle fibres. CRAB SPECIMENS (fig. 4)

The epithelium of the bursal canal is densely

stained because it receives the openings of shell Apart from the horseshoe crabs from which the

glands that surround it. This lining epithelium type-specimens of Ectoplana undata were ob- did show nuclei. The musculature of also not any tained, cocoons were found attached to the

bursal canal of of the is well developed, but a type gill leaves of other specimens Tachypleus gigas. that is difficult to interpret. It does not consist of Cocoons were found on T. gigas from Sumatra's

of circular and Sea regularly arranged rows east coast (fig. 4C), Java at Pekalongan (fig.

muscle ir- and another from Deli longitudinal fibres, but shows a more 4D), on specimen (fig.

and be regular arrangement. The major part consists 4E). The size shape of these cocoons can

less of more or circularly running muscles, in- derived from the figures. BIJDRAGEN TOT DE DfERKUNDE, 53 (2) - 1983 223

Cocoons obtained various horseshoe crabs. A: from which of undata Fig. 4. from Tachypleus gigas holotype Ectoplana n. sp.

B: T. from C: T. Sumatra’s D: T. Sea was collected, gigas which paratypes were collected, gigas, east coast, gigas, Java at

Pekalongan, E: T. gigas, Deli, F: Carcinoscorpius rotundicauda, Singapore, G: C. rotundicauda, Sabang.

found attached E. limuli. In E. of Interestingly, cocoons were undata the number testes is

also the of the horseshoe crab Carcinoscor- E. to gills small as compared with limuli, the former

rotundicauda. obtained from pius Cocoons were having 6-8 and the latter about 18 testicular

collected and Sabaner follicles either side of the specimens at Singapore on body. The male

also between both (figs. 4F, G). copulatory apparatus differs

species. In E. limuli the penis papilla is large

and whereas in E. undata it and DISCUSSION conical, is small

In E. undata the deferentia in- stubby. vasa open

Wilhelmi (1909) was the first to mention the to a rounded seminal vesicle, but in E. limuli

of marine triclads Asian horseshoe unite first into short presence on they a common duct which crabs. On preserved crabs from Singapore, subsequently expands slightly in diameter and

Wilhelmi found triclads which he thought to be thereafter narrows and opens into the tip of the

the of With the male bdellourids, although poor state preserva- penis papilla. respect to tion did allow him determination. another dif- not a specific copulatory apparatus important

Kaburaki between both the male Since Ijima & published their descrip- ference species concerns tion of limuli in Wilhelmi's atrium. In E. limuli there is and Ectoplana only 1916, only a small conclusion about the taxonomie status of his typical atrium which differs considerably from

is when the atrium of E. undata The specimens not surprising, especially as described above.

considers the external resemblance between female also one copulatory apparatus shows impor-

undata and of between In Ectoplana some specimens tant differences the two species. E.

limuli the bursal for its Bdelloura. canal has, greater part, a

from different host dorsoventral whereas in E. undata it Apart living on a species, disposition,

Common Ectoplana undata differs in several respects from runs obliquely. to both species is the 224 R. SLUYS - TRICLADS ON HORSESHOE CRABS

E. anterodorsal enlargement of the bursal canal, undata, I cannot rule out the possibility that

in E. although this is more developed limuli. small nuclei were obscured by the staining of

The bursal canal of E. limuli shows a number of these epithelia. Moreover, I could not find con-

laterally directed folds which exhibit bilateral clusive evidence for nuclei outside these

the bursal canal does This well with the situa- symmetry. In E. undata epithelia. agrees very

not show lateral outbulgings. In E. limuli the tion which Kaburaki (1922) described for the

oviducts into the dorsal of the bur- bursal canal of E. limuli. to this in- open portion According

in into the bursal canal of E. limuli "...is sal canal, whereas E. undata they open vestigator

the of latter. In both the ventral part the species surrounded by numerous pyriform cells which

shell into bursal close the insunken glands open the canal, to perhaps represent partly parts of

the openings of the oviducts. This implies that the lining epithelium and partly unicellular

in E. limulithe dorsal portion of thebursal canal glands". Concerning the epithelium lining the

receives the openings of shell glands, whereas in male atrium of E. limuli, Kaburaki (1922: 38)

E. undata the into the ventral that "...it shows no which are glands open por- wrote nuclei, ap- tion of the canal. parently displaced just beneath the muscular

In E. undata the distal A number of structural similarities between layer". only narrow, part

and undata be considered in- of the male atrium shows insunk E. limuli E. may an epithelium. dicative of the is described in close genealogical relationship The species that as new the between the of is the two species, although, course, a present paper, assigned to genus Ectoplana

formed after this is defined. definite hypothesis can only be a although at the moment poorly

of the of When Kaburaki transferred the comprehensive analysis entire group (1917) species marine triclads. Both show Procerodes limuli to the erected Ec- species (1) a penis newly genus

which papilla which is lined with an infranucleate toplana, he did not provide a definition

oviducts which receive the the from other Pro- epithelium, (2) open- distinguished genus ings of shell glands just before opening into the cerodidae. Kaburaki (1917) considered the bursal insunk of lateral in the bursal canal, (3) an epithelium lining presence outbulgings the bursal and difficult canal and the fact that the oviducts direct- canal, (4) an unusual, to open interpret type of musculature around the bursal ly into the canal, to be sufficient to maintainthe canal. With respect to the last-mentioned separate generic status of E. limuli. In his ex- feature Kaburaki (1922) also found the situa- tended description Kaburaki (1922) came to the tion difficult to interpret for his description is conclusion that the bursal canal of E. limuli not unequivocal. In E. limuli Kaburaki de- (which he called vestibulum) is homologous scribed the musculature of the bursal canal to with the bursal canal (which he calledvagina) of be "...for of three Stummeria This that the composed the most part... trigonocephala. implies

character of the viz. sets of fibres, viz. internal circular, middle defining genus Ectoplana, longitudinal and outermost circular, of which the "Oviducts opening separately into the extreme- middle circular layer is developed to a con- ly wide, dorsally prolonged vestibulum" siderable degree" (emphasis mine). This incon- (Kaburaki, 1922: 46), does not differentiate this sistent should be checked for Stummeria. The latter description on new genus from, example, materialof E. for the characterized Kaburaki limuli, type-specimens are genus was by (1922: lost, and compared with the situation found in 46) by its "Oviducts opening separately into the

E. undata. Kaburaki' s description of E. limuli vagina". Moreover, there are other Pro- and observations E. undata the cerodidae known in which the my on agree to to date, oviducts

that in both the of the into the bursal viz. extent species major part open separately canal, musculature around the bursal canal consists of Miroplana trifasciata Kato, 1931, Tryssosoma jen- circular muscles. With respect to the absence of nyae Ball, 1977, Sabussowia wilhelmi Ball, 1973, nuclei in the epithelium lining the bursal canal and S. dioica (Claparède, 1863). Thus, it is clear and the distal of that the portion the male atrium in genus Ectoplana needs redefinition or BIJDRAGEN TOT DE DIERKUNDE, 53 (2) - 1983 225

should be abolished. Of deci- triclads collected from of course, a proper no were specimens

without sion on the subject cannot be reached a Carcinoscorpius rotundicauda, it remains unknown

careful analysis of the Procerodidae as a whole, whether the cocoons attached to this horseshoe

for this "...is the of undata taxon one most badly in need crab came also from specimens E. or

of 1977: For the different of triclad. revision" (Ball, 25). moment I belong to a species

of the features which The of E. undata ob- can indicate only some type-specimens were

decide from made me to retain the genus Ectoplana tained from T. gigas collected widely

and the described found to assign newly species to separated areas, whereas cocoons were

this In four from still other genus. short, these are the on members of T. gigas areas.

characteristics listed which From this it be concluded most above, were con- may that, likely,

of close sidered to be indicative a genealogical the distribution of E. undata overlaps with the

between E. limuli and E. undata. entire of T. relationship range gigas (fig. 5). Carcinoscorpius

As can be seen in differences in rotundicauda has somewhat smaller fig. 4, some a range,

size could be observed between cocoons ob- which for an important part overlaps with that

tained different of of but also extends westward from specimens Tachypleus T. gigas, more (fig.

well between obtained from The of tridentatus and T. gigas as as cocoons 5). ranges Tachypleus

the same specimen of horseshoe crab. Because gigas overlap along the coast of Vietnam,

Fig. 5. Distribution of the Asian horseshoe crabs Tachypleus tridentatus, T. gigas and Carcinoscorpius rotundicauda (after

Pocock, 1902; Smedley, 1929; Waterman, 1958; present material). 226 R. SLUYS - TRICLADS ON HORSESHOE CRABS

Museum of Amsterdam, with reflections whereas those of T. gigas and C. rotundicauda some on

18th century shell cabinets and their proprietors, on overlap along the coast of the Malay Peninsula. occasion of the centenary of the Royal Zoological All three Asian horseshoe crabs occur in nor- Society "Natura Artis Magistra". Bijdr. Dierk, 27: thern Borneo It is not unreasonable to (fig. 5). 167-246.

that each of these 1933. KÜKENTHAL assume three, partly sym- BRESSLAU, E., Turbellaria. In: W. &

T. KRUMBACH, Handb. Zool., 2 52-293 patric, species of horseshoe crab has its own ec- (1): (Walter

de Gruyter & Co., Berlin, Leipzig). toparasitic species of marine triclad. Only fur- IJIMA, J. & T. KABURAKI, 1916. Preliminary descriptions ther efforts collecting on preserved or living of some Japanese triclads. Ann. zool. Jap., 1: 153- crabs the answer. may provide 171.

KABURAKI, T., 1917. Notizen über japanische Tricladen

Ann. zool. Jap., 9 (3): 325-333.

ACKNOWLEDGEMENTS Tricladida , 1922. On some Japanese Maricola, with

the classification of the a note on group. Tokyo imp. wish Prof. Dr. Ian R. Ball for I to thank comments on the Univ. J. Coll. Sei., 44: 1-53. of this and also for manuscript paper giving me access to R. 1902. The of of POCOCK, I., recent species his private reprint collection from which I could obtain Limulus. Ann. Mag. nat. Hist., (7) 9: 256-266. the triclads. easily necessary literature onJapanese marine SMEDLEY, N., 1929. Malaysian King Crabs. Bull. Raffles

Mus., 2: 73-78.

WATERMAN, T. H., 1958. On the doubtful validity of REFERENCES hoeveni Indonesian Tachypleus Pocock, an horseshoe

BALL, I. R., 1977. On the phylogenetic classification of crab (Xiphosura). Postilla, Yale Peabody Mus. nat.

aquatic planarians. Acta zool. Fenn., 154: 21-35. Hist., 36: 1-17.

BENTHEM JUTTING, W. S. S. VAN, 1939. A briefhistory of WILHELMI, J., 1909. Tricladen. Fauna Flora Golf.

the conchological collections at the Zoological Neapel, 32: 1-405.

Received: 1 July 1983