Micropecten excuratus, Dijkstra & Maestrati, 2012

Dijkstra, Henk H. & Maestrati, Philippe, 2012, Pectinoidea (Mollusca, Bivalvia, Propeamussiidae, Cyclochlamydidae n. fam., Entoliidae and Pectinidae) from the Vanuatu Archipelago, Zoosystema 34 (2), pp. 389-408 : 396-397

Micropecten excuratus n. sp.

( Fig. 1 F-J)

TYPE MATERIAL. — Vanuatu. SANTO 2006, stn DS101, 15°32.3’S, 167°17.2’E, 17-19 m, holotype lv ( MNHN 24273 ) , 10 paratypes lv, 14 paratypes rv ( MNHN 24274 ), 1 paratype lv, 1 paratype rv ( ZMA Moll. 4.11.015) .

TYPE LOCALITY. — Vanuatu Archipelago, north of Tutuba Island , 15°32.3’S, 167°17.2’E, 17-19 m, sand (SANTO 2006 stn DS101) .

DISTRIBUTION. — Known only from the type locality, collected dead in 17- 19 m.

ETYMOLOGY. — From the Latin adjective “excuratus”, meaning well-groomed or well-dressed, with reference to the abundantly sculptured disc of this micro-scallop.

DESCRIPTION

Shell up to c. 2.5 mm high, fragile, hyaline, subcircular, slightly posteriorly oblique, inequivalve, inequilateral, left valve more inflated than right valve; translucent, prodissoconch of left valve conical, of right valve flat.

Left valve (holotype) disc and auricles sculptured with numerous narrow antimarginal lirae, secondary riblets in interspaces, and delicate commarginal lirae, commencing in early growth stage. Auricles subequal, anterior one slightly larger than posterior one. Prodissoconch c. 230 µm wide, conical, sculptured with a web-like pattern of raised tracery.

Right valve (paratype) disc and ventral half of posterior auricle similarly sculptured with narrow antimarginal lirae; intercostal secondary riblets in late growth stage. Longitudinal hexagonal microscructure. Posterior auricle continuous with disc, anterior one demarcated and sculptured with a few fine nodulous radial riblets. Byssal notch relatively deep. Prodissoconch flat and similarly sculpture as prodissoconch of left valve.

Dimensions of holotype (left valve): H 2.4 mm, W 2.4 mm.

REMARKS

Micropecten excuratus n. gen., n. sp. is morphologically closest to Micropecten plectofilum (Oliver & Holmes, 2004) n. comb., known from Rodrigues (Indian Ocean, Mascarene Islands; dead at 17 m depth). Both species have a similar size ( M. excuratus n. gen., n. sp. 2.5 mm in height, M. plectofilum (Oliver & Holmes, 2004) n. comb. 2 mm), are slightly posteriorly oblique, and have an antimarginal sculpture on the right valve. However, M. excuratus n. gen., n. sp. has more regularly spaced antimarginal sculpture, commencing at an earlier stage on the right valve, and M. excuratus n. gen., n. sp. also has a commarginal sculpture on the left valve, which is lacking in M. plectofilum (Oliver & Holmes, 2004) n. comb.

Figures

FIG. 1. — A-E, Holotype of Cyclochlamys aperta n. sp. (MNHN 24271); A, B, external views of left and right valve; C, left valve prodissoconch; D, right valve detail; E, right valve prodissoconch; F-J, Micropecten excuratus n. gen., n. sp.; F, holotype (MNHN 24273), external view of left valve; G, paratype (MNHN 24274), external view of right valve; H, holotype, left valve prodissoconch; I, paratype, right valve detail; J, paratype, right valve prodissoconch. Scale bars: A, B, F, G, 500 µm; C-E, H-J, 100 µm.