Cysticolous Myzostomida, Notopharyngoides Platypus from Comanthina Nobilis (Echinodermata: Crinoidea), at Kushimoto, Honshu, Japan
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Species Diversity, 1998, 3, 17-24 Cysticolous Myzostomida, Notopharyngoides platypus from Comanthina nobilis (Echinodermata: Crinoidea), at Kushimoto, Honshu, Japan Mark J. Grygier1 * and Keiichi Nomura2** 'Tropical Biosphere Research Center (Sesoko Station), University of the Ryukyus, Sesoko 3422, Motobu, Okinawa 905-0227, Japan 2Kushimoto Marine Park Center, Arita 1157, Kushimoto, Wakayama 649-3514, Japan (Received 17 February 1997; Accepted 3 September 1997) About 20% of individuals of the comatulid crinoid Comanthina nobilis (Carpenter, 1884) at Shionomisaki, the southernmost point of the island of Honshu, Japan, are infested by the cysticolous myzostomidan worm originally described asMyzostoma platypus Graff, 1887. Up to four cysts per host occur. This parasite had been collected previously only in the Philippines by the 'Challenger' Expedition, from the same host species. The present specimens differ in having a few to many supernumerary marginal cirri and up to six (versus three to five) separate tabular outgrowths in a row along the ventral midline. It is proposed to reassign this species as the most plesiomorphic member of the genus Notopharyngoides Uchida, 1992. Key Words: Myzostomida, Notopharyngoides platypus, Crinoidea, Comanthina nobilis, Japan, redescription, range extension, cysticole, marine parasitology. Introduction Carpenter (1888) described in detail the comasterid crinoid Actinometra (now Comanthina) nobilis Carpenter, 1884 based on the holotype from 'Challenger' sta. 208 (Philippines, 11°37'N, 123°31'E, 33m) and five additional specimens from Samboangan (i.e., Zamboanga, Philippines); he had formerly considered the latter as representing a distinct species. The holotype of A. nobilis and one of the other specimens bore uncalcified cysts on the disc, and the aperture of each cyst opened close to an ambulacral groove. Carpenter (1888: pi. LXV, fig. 8) illustrated three such cysts on one host, a specimen from Zamboanga according to Carpenter's letter quoted by Graff (1887). Perhaps in error, this letter said there were six specimens of A. nobilis from that place, not only five. Carpenter sent another cyst from the same host individual to Graff, who described the single myzostome found therein as Myzostoma platypus (see Graff 1887:13-14, pi. Ill, figs 7-12). Graffs holotype of M. platypus was not found (by MJG) among other 'Challenger' material during a visit to The Natural History Museum in London in 1986. The only subsequent study of M. platypus was a histological investigation by Wheeler (1896:244-246, 276, 279-280, pi. 11, figs 26-30). lie found a specimen of A. nobilis in the London museum with many cysts on the disc and arm bases, removed the single myzostome from nine of them, and sectioned eight worms; these sections *Current address: Lake Biwa Museum, Oroshimo 1091, Kusatsu, Shiga 525-0001, Japan " Current address: Yaeyama Marine Park Research Station, Kuroshima, Taketomi, Okinawa 907-1311, Japan 18 M. J. Grygier and K. Nomura are currently housed in The Natural History Museum, but the unsectioned specimen was not found there in 1986. Wheeler neglected to mention where the crinoid had been collected. All the sectioned specimens were late hermaphrodites with reduced male organs. Wheeler (1896) also found from one to five endoparasitic trematodes, which he named Disloma myzostomatis, in the parenchyma of the wall of the pharynx (i.e., the introvert) in each sectioned specimen. In a review of crinoid associates, Clark (1921) reported the host of M. platypus as Comanthina schlegelii (Carpenter, 1879), but Rowe et al. (1986) once again recog nized C. nobilis as a separate species. Clark (1921) reported Singapore as well as Zamboanga as a locality for this myzostome, but we have been unable to find a record from Singapore in any primary literature and assume that Clark was mis taken. Family Myzostomatidae Beard, 1884 Genus Notopharyngoides Uchida, 1992 Notopharyngoides platypus (Graff, 1887), n. comb. Material. Prevalence (frequency of infestation) of Comanthina nobilis at Shionomisaki, Kushimoto, Honshu, Japan, about 20%, with one to four cysts per infested crinoid (Fig. 1). Specimens examined in detail include three from one host, 6 November 1996, coll. K. Nomura (crinoid caught in lobster net) and two specimens from another host, 7 December 1996, 15 m, coll. K. Nomura (SCUBA). Host species identified (by KN) using key of Kogo (1995). All specimens deposited in Osaka Museum of Natural History (OMNH-Iv 1495-1499). Disc of second infested crinoid, a dissected cyst from first crinoid, and worms isolated from both hosts were photo graphed; worms were also examined under binocular dissecting microscope. Two 'parapodia' (right legs 3 and 4) of damaged specimen partly dissolved in weak bleach and mounted on slide in glycerine jelly in order to study hook apparatus under compound microscope. Description of cyst. Only one intact cyst examined in detail (Fig. 2a): irregularly subspherical, about 4.8mm long and 4.0mm wide, soft and uncalcified, with 1.3mm diameter circular aperture adjacent to ambulacral groove, and lip of latter notched at that spot. Myzostome within cyst (Fig. 2b,c) oriented with posterior end toward aperture and ventral side upwards. Description of myzostome. Specimens round to oval and highly convex ventrally, variably concave dorsally (Figs 2-4). Dorsal side smooth. One specimen from first host (not illustrated) 4.15mm in diameter, its dorsum 3.8X 3.3mm, askew from normal body axes; another specimen damaged (nearly cut in half transversely), 5.65mm wide; third specimen (Fig. 2b,c) 4.1mm wide, 3.9mm long. One specimen from second host (Fig. 4) with dorsum 4.1mm long, 3.5mm wide, the other specimen (Fig. 3) 2.8mm long, 3.6mm wide. Body margin developed into membranous, cirrus-bearing flange in one specimen, but not especially thin in other specimens. Two specimens with 21 marginal cirri each, and another with 23, arranged somewhat irregularly (missing from a few sites if meant to be spaced evenly, and including small posterior clump of supernumerary cirri, some of these bifid). Another specimen with 30 marginal cirri [one cirrus bifid (Fig. 3b) and supernumerary ones mostly at rear], and the last with 45-46 cirri Cysticolous Myzostomida Notopharyngoides platypus 19 spaced quite unevenly and including two bifid cirri and one multifid cirrus. On ventral side, no submarginal shelf or lappets present, but fairly distinct line in one specimen marks boundary of some sort near edge. Row of six flat-topped, sometimes apically flared outgrowths along ventral midline in two specimens (Fig. 2b), first such process longest, remainder more or less round to cat's-eye-shaped. In another individual, second and third processes narrowly joined. In two others (Figs 3a, 4), both second and third, and fourth and fifth joined. In all specimens, introvert pouch opening at base of front end of first mid-ventral process (Fig. 5). Ano-genital opening, when visible, found at posterior edge of rearmost process or, in one specimen, on barely separated ano-genital cone behind it, in each case quite close to body margin. Introvert fully retracted (Fig. 2c) or with its distal end exposed (Fig. 4b) or fully protruded (Fig. 3). Total length of introvert up to 1.5 mm. Conical, radially furrowed distal part of introvert enclosing laterally compressed mouth and surrounded by lip bearing corona of seven or eight pairs of triangular, distally acuminate buccal papillae (number varying among three specimens in which they could be counted accurately). Gap between ventralmost pair of papillae. Five pairs of 'parapodia' (legs; best displayed in Fig. 4a), each with stubby, blunt distal part arising from gap in broad, heart-shaped proximal fold. In one specimen, outer lobes of these folds sometimes bent away from general body surface. Folds of similar size in all legs, except sometimes one or both of fifth pair smaller. Hook apparatus consisting of hook, smaller replacment hook of variable size, and support rod (Fig. 6). Hooks in examined specimen 656-670/zm long, 56//m wide, distal quarter bowed very slightly outward and tip forming an evenly tapered, rounded hook of less than 90°. Support rods 25% longer than hooks, slightly thicker than hooks for most of length but almost 40% thicker at base, distal third tapered and slightly curved; interior of shaft hollow distally; manubrium developed only on inner side of tip, curving around inner margin of hook and bearing many small, rounded, irregularly placed lobules along its own inner margin. Third pair of 'parapodia' associated with pair of penes up to 2.1mm long arising from their outer bases. Two specimens with one penis protruded like large, tapered, translucent cannon (tip may be curved) and other penis retracted as small knob (Fig. 3). In another specimen, one penis fully protruded, the other one halfway so (Fig. 5). In damaged specimen, right penis lost, but left one long and thick with abnormally swollen distal part and narrow tip (Fig. 5). In final specimen, both penes protruding equally but not reaching body margin (Fig. 2b). Four pairs of large, circular, distinctly yellowish lateral organs (in contrast to creamy white color of remainder of formalin-preserved body), each centered about halfway between outer edges of 'parapodia' and body margin, similar in form but protruding to different degrees in different specimens (best displayed in Fig. 3a). Lateral organs consisting of short stalk, outer ring with diameter greater than stalk, more heavily pigmented but narrow ring inside this, and inner dome-like zone with exposable and protrusable central button; when button exposed, inner rim of dome radially grooved. Remarks. The present specimens differ from those described by Graff (1887) and Wheeler (1896) in having more than 20 marginal cirri (in two cases many more) and in having up to six rather than three to five mid-ventral processes. However, in Graff's (1887) drawing the fourth mid-ventral process corresponds to the coalesced 20 M.