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Population and developmental characteristics of the rhizocephalan parasite Sacculina carcini were studied in the Limfjord, Denmark and at Roscoff, France. The frequency of juvenile externae...

北太平洋に面する岩手県三陸町吉浜湾船作海岸の潮間帯から採集した短尾類と異尾類に寄生する根頭類と等脚類を調べた. イワガニにヤツフクロムシ(新称)Sacculina yatsui, イソガニにフクロムシ属の1種Sacculina sp., ホンヤドカリ属の1種Pagurus maculosus(新宿主)にナガフクロムシPeltogaster paguri, ホンヤドカリ(新宿主)・テナガホンヤドカリ・P. maculosus(新宿主)にフサフクロムシPeltogasterella gracilis, ホンヤドカリとP. maculosus(新宿主)にヤドカリノハラヤドリAthelges takanoshimensisを認めた. これらの寄生虫は本海域から初記録であり, その出現状況, 形態, 分布を記述した., Four species of Rhizocephala were found on crabs from the intertidal rocky shore of Sanriku, northern Honshu: Sacculina yatsui Boschma, 1936 from Pachygrapsus crassipes; Sacculina sp. from Hemigrapsus sanguineus; Peltogaster paguri Rathke, 1842 from Pagurus maculosus (new host); and Peltogasterella gracilis (Boschma, 1927) from Pagurus filholi (new host), P. maculosus (new host) and P. middendorffii. The bopyrid isopod Athelges takanoshimensis Ishii, 1914 also occurred on P. filholi and P. maculosus (new host). These parasitic crustaceans are recorded for the first time from the Pacific coast of northern Honshu.

FAMILY GALEOMMATIDAE GRAY, 1840 Shell slightly convex or flattened, often gaping ventrally, umbones median or submedian. Hinge edentulous or with one tuberculiform cardinal in each valve, sometimes with a second and smaller cardinal present; a short posterior lateral is often present. Internal ligament opisthodetic, in a small pit or groove. The expanded mantle more or less covers the exterior of the shell. The shells of the Galeommatidae are usually thin, brittle and featureless. The hinge is edentulous, irregular or often with one stout cardinal in each valve, sometimes with a second and smaller cardinal present in the left valve. The shell is more or less internalized by the profuse development of the mid-mantle folds, which are wrapped over the shell and, when fully extended, may cover both valves, sometimes permanently. In most species the mid-mantle folds can be withdrawn completely between the valves when the animal is disturbed. Inner folds of the mantle are fused posteroventrally to separate a wide anterior inhalant-pedal gape from a much smaller posterodorsal exhalant aperture, which is often raised on a short siphon. Anteriorly, the free and often frilled edges of the mantle folds normally extend beyond the shell edges as an extensive cowl or hood. It forms a poorly defined inhalant siphon for the anterior-to-posterior water flow through the mantle cavity. When the mantle is fully extended over the shell, the shell is only exposed at a minute oval opening above the umbones or at a slit in the mid-lateral region. The exposed parts of the mantle may be completely naked, but are normally ornamented with sensory tentacles or papillae, whose tips may be pointed or blunt and are sometimes pigmented (whitish, yellow or red). The distinction between papillae and tentacles is based on size and length rather than on histological criteria. Both can be extended by swelling of interior haemocoelic spaces and shortened or withdrawn by contraction of longitudinal muscle fibres (Morton, 1973; O’Foighil & Gibson, 1984; Mikkelsen & Bieler, 1989). Two fairly large unpaired tentacles arise dorsal to the anterior hood and to the exhalant aperture in many species and in some are the only tentacles present. They are called anterior and posterior siphonal tentacles. In some species (e.g. Scintilla longitentaculata sp. nov.) they can be everted suddenly from the normal retracted position and waved vigorously, probably to divert or dissuade potential predators, and are then known as dymantic tentacles (Morton, 1975). In species of Galeomma, the papillae may have a terminal swelling which autotomizes and, it is believed, releases a noxious substance which may deter would-be predators (Morton, 1973). Preserved specimens are often more or less retracted into the shell, with the tentacles protruding only slightly beyond the edges of the gaping shell. Only Aclistothyra has the mantle edges fused along the dorsal mid-line and is unable to retract. The muscular foot is adapted for active crawling, as described by several authors (e.g. Arakawa, 1960, 1961). A byssus gland is present and a few fine byssal threads attach the bivalves to the underside of stones, crevices, coral galleries and other protected substrates. A number of species are commensal with burrowing crustaceans or echinoderms. Some species are largely solitary, while others are gregarious, gathering in small groups that may sometimes consist of more than one species. The eggs are incubated in the suprabranchial chamber, which includes both inner and outer demibranchs. Most of the species which have been studied are hermaphroditic. The systematics of this family is in need of revision, with emphasis on both shell and soft part characters. Our studies indicate that several species have been named many times, probably as a result of the old habit of studying only cleaned shells. We have followed a conservative line and hope that additional information will emerge from molecular studies of the specimens that we have collected at Phuket., Published as part of Lützen, Jørgen & Nielsen, Claus, 2005, Galeommatid bivalves from Phuket, Thailand, pp. 261-308 in Zoological Journal of the Linnean Society 144 (3) on pages 263-264, DOI: 10.1111/j.1096-3642.2005.00168.x, http://zenodo.org/record/5434040, {"references":["Morton B. 1973. The biology and functional morphology of Galeomma (Paralepida) takii (Bivalvia: Leptonacea). Journal of Zoology, London 169: 133 - 150.","O'Foighil D, Gibson A. 1984. The morphology, reproduction and ecology of Scintillona bellerophon spec. nov. (Galeommatacea). Veliger 27: 72 - 80.","Mikkelsen PM, Bieler R. 1989. Biology and comparative anatomy of Divariscintilla yoyo and D. troglodytes, two new species of Galeommatidae (Bivalvia) from stomatopod burrows in eastern Florida. Malacologia 31: 175 - 195.","Morton B. 1975. Dymantic display in Galeomma polita Deshayes (Bivalvia: Leptonacea). Journal of Conchology, London 28: 365 - 369.","Arakawa KY. 1960. Some ecological accounts on Scintilla vitrea (Quoy & Gaimard). Venus 21: 61 - 66.","Arakawa KY. 1961. A note on the animal of Scintilla violescens collected in Genkai Sea. Venus 21: 143 - 146."]}

GENUS EPHIPPODONTA TATE, 1889 Shell semielleptical, laterally angular, most extended not far from straight hinge margin, ventrally rounded. Externally smooth, striated, papillose or reticulated. Internal ligament bounded on each side by obtuse tooth with bifid crown. Shell more or less internalized by overgrowth of the papillose mantle. Type species: Scintilla lunata Tate, 1886. Remarks The genus is divided into three sub-genera (Ephippodonta, Ephippodontoana and Ephippodontina)., Published as part of Lützen, Jørgen & Nielsen, Claus, 2005, Galeommatid bivalves from Phuket, Thailand, pp. 261-308 in Zoological Journal of the Linnean Society 144 (3) on page 302, DOI: 10.1111/j.1096-3642.2005.00168.x, http://zenodo.org/record/5434040, {"references":["Tate R. 1889. New species of marine Mollusca from South Australia and Victoria. Transactions of the Royal Society of South Australia, Adelaide 11: 60 - 66."]}

GENUS ACLISTOTHYRA MCGINTY, 1955 The valves are thin, nearly flat, about half as high as long, broadly gaping. They are rounded, not angular, at the ends of the straight hinge-line. The minute submedian umbones are convex and rounded. Hinge margin very thin but slightly thicker medially, without teeth. Shell entirely and permanently covered by mantle except for a small circular foramen near umbo. A series of cylindrical pointed tentacles arise from the mantle peripherally to the shell margins (emended from McGinty, 1955). Type species: Aclistothyra atlantica McGinty, 1955 (monotypy). Remarks The genus is close to Ephippodonta, differing mainly in the complete absence of hinge teeth. Whether it also should be included in that genus must await further study of the soft parts and interior anatomy. ACLISTOTHYRA ORIENTALIS SP. NOV. (FIGS 6I, 51D- F) Material examined Holotype: PMBC 20118, reef off PMBC, Thailand, no date, SL = 8.5 mm. Paratype: Reef off PMBC: no date, one specimen. Description of material from Phuket Shell: Smoothly and regularly elongate ovate, very thin and brittle, almost translucent, whitish, slightly shining, surface completely smooth without any sculpturing. Almost flat except for slightly vaulted area near the small umbo, which is located in the middle. Hinge margin nearly straight along the middle third, emarginated anteriorly and posteriorly. Shell margins rounded at both ends. Size of two specimens 8.5 ¥ 4.9 mm and 10.0 ¥ 5.1 mm. The prodissoconch II is large, 400 Mm in diameter. Hinge plate in both valves an elongate, rounded edentulous bar, with an external ligament only, a resilifer being absent. Soft parts: The valves of one of the specimens were held horizontally; in the other they gaped about 90∞. The shell is overlain by a thin sheet of the reflected mantle except for a small circular foramen in front of the umbones. All along the shell margins the mantle continues as a dorsoventrally flattened girdle peripherally terminating in an edge which sharply divides the mantle into dorsal and ventral parts. Many relatively long cylindrical pointed tentacles issue all along the mantle edge. They number 30–35 on each side and are most crowded anteriorly and posteriorly. Their length varies, probably according to their relative state of retraction. The dorsal part of the mantle is everywhere beset with numerous regularly spaced wart-like papillae, which are also present in a narrow marginal zone on the mantle’s ventral part. The anterior inhalant region is a vertical slit connecting ventrally with a large pedal gape. A pair of close-set siphonal tentacles guards the dorsal margin of the inhalant aperture. They are similar to the marginal tentacles, but larger. The exhalant opening in both preserved bivalves is small and provided with a single short, thick and pointed posterior siphonal tentacle. Whether the inhalant and exhalant openings may be protruded siphon-like in life as in some species of Ephippodonta is unknown. Distribution Phuket Island, Thailand (present study). Remarks In several galeommatid genera the valves gape widely and the animals are limpet-like. Shell characteristics, such as shape, thinness, lack of a distinct ornamentation, and especially the complete edentulous condition of the hinge, place the present species in Aclistothyra, but the soft parts cannot be compared, as they are unknown in the only other described species, A. atlantica McGinty. In the likewise limpet-like Ephippodonta the shells are also dorsoventrally flattened. Species of the subgenera Ephippodonta and Ephippodontoana have a shell ornamentation of distinct papillae; this is developed only toward the margin in the former, while it is arranged along radiating dichotomously branching riblets in the latter. In both subgenera the hinge bears interlocking cardinals and laterals. In the subgenus Ephippodontina the surface of the shell is finely reticulate. Dentition is rather well developed except in E. (Ephippodontina) oedipus Morton in which only questionable laterals are preserved. The only species of Ephippodonta with a smooth shell surface like that of the present species is E. gigas; in the latter, however, the cardinals as well as a resilium have been preserved (Kubo, 1996). In limpet-like galeommatids true marginal tentacles similar to those of A. orientalis, rather than an incised mantle margin, occur in E. gregaria Gofas (assignation to subgenus dubious) and E. (Ephippodontina) murakamii Kuroda, but the tentacles in these species are smaller and more, or much more, numerous. Etymology The species is named after the geographical region where it was found., Published as part of Lützen, Jørgen & Nielsen, Claus, 2005, Galeommatid bivalves from Phuket, Thailand, pp. 261-308 in Zoological Journal of the Linnean Society 144 (3) on pages 304-305, DOI: 10.1111/j.1096-3642.2005.00168.x, http://zenodo.org/record/5434040, {"references":["McGinty TL. 1955. New marine mollusks from Florida. Proceedings of the Academy of Natural Sciences, Philadelphia 107: 75 - 85.","Kubo H. 1996. Ephippodonta gigas n. sp. (Bivalvia: Galeommatoidea) from Okinawa Island, southwestern Japan. Venus 55: 1 - 5."]}