Cyclochlamys wakensis Dijkstra & Raines, 2013
DIJKSTRA, H. H. & B. K. RAINES. 2013. A new living species of Cyclochlamys (Bivalvia, Pectinoidea, Cyclochlamydidae) from Wake Atoll (Pacific). Basteria, 77 (1-3): 17-21, figs. 1-9. [p. 18, figs. 1-8]
2013 Cyclochlamys wakensis Dijkstra & Raines, 2013
H. H. Dijkstra & B. K. Raines, 2013, figures 1-8.
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«Type material. — Holotype (lv, LACM 3236). Paratypes (LACM 3237, 1: Figs 3, 4; LACM 3239, 1: Fig. 8; LACM 3240, 1: Fig. 5; LACM 3256, 1: Fig. 7; LACM 3257, 1: Fig. 6; LACM 3238, 5; ZMAMoll. 391595, 15). All paratypes from type locality.
Measurements of type material: Holotype (lv, LACM 3236) height 1.8 mm, length 1.9 mm; figured paratype (rv, LACM 3237) height 1.1 mm, length 1.1 mm; figured paratype (lv, LACM 3239) height 1.9 mm, length 1.9 mm; figured paratype (lv, LACM 3240) height 1.4 mm, length 1.4 mm; 7 paratypes (5 lv and 2 rv, LACM 3238) height lv 1.5 mm to 2.2 mm, length lv 1.5 mm to 2.3 mm, height rv 1.1 mm to 1.4 mm, length rv 1.2 to 1.5 mm; 15 paratypes (11 lv and 4 rv, ZMAMoll. 391595) height lv 1.7 to 2.2 mm, length lv 1.7 mm to 2.3 mm, height rv 1.1 mm to 1.9 mm, length 1.1 mm to 1.9 mm.
Type locality. — Pacific: Wake Atoll, off the south side of Wake Island, 19˚17’24”N, 166˚36’33”E, 15-18 m, dead, sand and rubble, leg. B.K. Raines, vi. 2012.
Description. — Shell up to 2.2 mm high, strongly inequivalve, left valve slightly more inflated than right valve, inequilateral, nearly circular to posteriorly oblique, about as wide as high, opaque whitish. Outline irregular, variable, typically changing during ontogeny, in most specimens associated with change in spacing of commarginal lamellae, direction of radial riblets.
Prodissoconch 215 μm high (fig. 2), roundly conical, PI and PII boundary unclear; sculptured with fine, crisp, irregularly anastomosing threads, more pronounced near boundary; anterior boundary indented (rudimentary byssal notch). Dissoconch left valve disc (0.3 mm) commencing immediately after prodissoconch boundary, without a border formed by strong flange-like commarginal rim (see Dijkstra & Marshall, 2008), weakly sculptured by 7 to 10 short and long irregularly spaced radial threads. Commarginal lamellae distinct throughout (figs 1, 8), faint throughout (fig. 5), weak in early growth stage (fig. 6) or faint in late ontogeny (fig. 7), commencing after 0.3 mm high, developed to the shell margin, variable in number (10-20), with weak tubercles on 7 or 8 intersections of commarginal lamellae, small radial riblets; interspaces more or less as wide as those of commarginal lamellae, widest over centre of disc, bearing delicate closely spaced radial threads. Auricles continuous with shell disc, similarly sculptured. Prodissoconch right valve disc slightly inflated, similarly sculptured as prodissoconch of left valve; surface of shell disc with outer layer of commarginally elongated, hexagonal prisms, each prism c. 40 μm wide and c. 8.5 μm high in centre of disc; posterior auricle continuous with shell disc, anterior auricle strongly declined, with 4 or 5 tubercular radial riblets. Byssal notch of moderate depth, byssal fasciole rather broad. Distribution.— Wake Atoll, 15-18 m, sand and rubble. So far only single valves have been sampled. It is most likely that the present species is living somewhat deeper.
Comparison.— Cyclochlamys wakensis spec. nov. is morphologically closest to the similarly sized congeneric species C. incubata (see Hayami & Kase, 1993: 62, figs 202-212), recorded from the Ryukyu Islands, Japan. Both species differ strongly in sculpture of the left valve. Cyclochlamys wakensis has strongly variable, prominent commarginal sculpture, whereas C. incubata has reticulate sculpture of equally developed radial and commarginal riblets. The commarginal sculpture of C. wakensis also commences later in the dissoconch stage (after c. 3 mm below the prodissoconch boundary) than of C. incubata (after c. 1 mm). The weak and small radial riblets are fewer and more widely spaced in C. wakensis, more equally spaced and more numerous in C. incubata. Moreover, C. wakensis has closely spaced intercommarginal secondary radial threads, which C. incubata lacks. The other 12 species of Cyclochlamys from the southwestern Pacific mainly differ from C. wakensis in having a different prodissoconch and sculpture of the left valve (Dijkstra & Maestrati 2010: 341, figs 3A-E; 2012: 394, figs 1A-E; Dijkstra & Marshall, 2008: 22-37, figs 20-29). Remarks.— Representative species of Cyclochlamys are principally recorded from the southern hemisphere (Southern Ocean, southern Australia and New Zealand region) and are not recorded from the Atlantic Ocean and Indian Ocean. Only four species are presently known from the tropical western and southwestern Pacific, i.e. C. incubata from Japan and Vanuatu, C. wakensis from the Wake Atoll, C. aperta Dijkstra & Maestrati, 2012 from Vanuatu, and C. australensis Dijkstra & Maestrati, 2010 from the Austral Islands. Most species (10) are recorded from the New Zealand region. Cyclochlamys species are not yet known from the Philippine and the Indonesian Archipelagos, probably due to proper sampling techniques (brushing technique of epibenthos on hard substrates) not being used or by erroneously determining these micromolluscs as juveniles of Pectinoidea. Etymology. — Named after the remote coral Wake Atoll in the northwestern Pacific.» HENK H. DIJKSTRA & BRET K. RAINES, 2013
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