Ephippodonta (Ephippodontina),

Lützen, Jørgen & Nielsen, Claus, 2005, Galeommatid bivalves from Phuket, Thailand, Zoological Journal of the Linnean Society 144 (3), pp. 261-308 : 302-304

EPHIPPODONTA (EPHIPPODONTINA) GIGAS KUBO, 1996

( FIGS 6H , 51A- C , 52 )

Ephippodonta (Ephippodonta) gigas Kubo, 1996: 1–5 , figs 1–6.

Ephippodonta (Ephippodonta) gigas: Higo et al., 1999: 460 , B660.

Material examined

New material: Reef off PMBC: 3 March 1975, four specimens ; 10 March 1982, three specimens . Koh Rok,

Phuket Island : 7 March 1982, one specimen ( PMBC 20117 ) .

Description of material from Phuket

Shell: Semicircular, acuminate at both ends, compressed, glossy white, smooth and transparent. Often with very distinct commarginal lines. Size of eight specimens ranges from 6.1 ¥ 2.5 to 16.0 ¥ 6.5 mm, but Okinawa specimens may attain an SL of 19 mm. The prodissoconch II in our specimens is 300 Mm across, but 200 Mm in bivalves from Okinawa ( Kubo, 1996). Umbo slightly in front of middle. Hinge margin straight, internal ligament situated between two small cardinal teeth.

Soft parts: The shell is completely covered by the reflected middle mantle lobe, which bears numerous incubated in a pair of pallial pouches in the female ( Morton, 1976). Such males were absent in specimens of the present species of which two sectioned specimens were a male (SL 6.1 mm) and a hermaphrodite (SL 12.9 mm).

small spherical papillae. Inhalant and exhalant siphons open at anterior and posterior margin in the median line, and are each provided with a single eversible siphonal tentacle. Inhalant siphon petaloid, larger than exhalant siphon. When fully extended, the mantle forms a horizontal membrane which along its margin is split into many relatively short, pointed and often branching fringes.

Habitat

At Phuket the species is found attached to undersurfaces of stones, often buried deep down (15 cm) in the sandy substrate. Of the eight specimens there were two groups of three and four. The first group was found within a mud tube probably inhabited by a thalassinidean shrimp. A similar association between the burrowing thalassinidean Axius plectorhynchus and Ephippodonta (Ephippodonta) lunata and E. (Ephippodontoana) macdougalli Tate, 1889 was noted by Tate (1889) and Matthews (1893). Kubo (1996) did not observe commensalism in his specimens.

Distribution

Okinawa Island, SW Japan ( Kubo, 1996); Phuket Island, Thailand (present study).

Remarks

The semielliptical shell and the absence of radial papillae place the species in the subgenus Ephippodontina (not Ephippodonta as suggested by Kubo). In E. (Ephippodontina) oedipus Morton , dwarf males are

Figures

Figure 6. A, Galeomma (Amphilepida) obockensis, reef off Nai Yang, 7 July 1976, PMBC ref. coll. 916, M102. B, G. (Galeomma) ambigua, reef off PMBC, 9 February 2003, PMBC ref. coll. 20114. C, G. layardi, reef off PMBC, 3 February 2003, PMBC ref. coll. 20113. D, holotype of G. phuketi sp. nov., reef off PMBC, 21 March 1975, PMBC ref. coll. 20115. E, Pseudogaleomma japonica, reef off PMBC, 3 March 2002, PMBC ref. coll. 20116. F, holotype of Nudiscintilla glabra gen. et sp. nov., reef off PMBC, 8 February 1975, PMBC ref. coll. 20111. G, holotype of S. ovalis sp. nov., reef off PMBC, 3 March 2002, PMBC ref. coll. 20112. H, Ephippodonta gigas, Koh Rok, Phuket Island, 7 March 1982, PMBC ref. coll. 20117. I, holotype of Aclistothyra orientalis sp. nov., shells photographed with soft parts inside; reef off PMBC, PMBC ref. coll. 20118. Top: right valve; bottom: left valve, except G (left valve). Scale bar = 5 mm.

Figure 51. Ephippodonta (Ephippodonta) gigas (A-C) and Aclistothyra orientalis sp. nov. (D-F). A & D, dorsal view of animal, anterior end at the top. B & E, left valve seen from outside. C, hinge viewed from inside, left valve above. F, right valve hinge. Scale bars: A, B, D, E = 5 mm, C, F = 1000 Mm.

Figure 52. Ephippodonta (Ephippodonta) gigas. Dorsal view of animal. Scale bar = 5 mm.