Similipecten herosae, Dijkstra & Maestrati, 2008

Dijkstra, Henk H. & Maestrati, Philippe, 2008, New species and new records of deep-water Pectinoidea (Bivalvia: Propeamussiidae, Entoliidae and Pectinidae) from the South Pacific, Mémoires du Muséum national d'Histoire naturelle 196, pp. 77-114 : 100-101

Similipecten herosae n. sp.

Figs 36-41

TYPE MATERIAL. — Holotype (spm) MNHN 20461 and 15 paratypes MNHN 20462-20463 , 2 HD.

TYPE LOCALITY. — Tonga, 18°41’S, 174°02’W, 76-85 m [BORDAU 2: stn DW 1581] .

DISTRIBUTION. — Only taken in the upper bathyal zone (see type locality) from Tonga.

MATERIAL EXAMINED. — Tonga. BORDAU 2: stn DW 1581, 18°41’S, 174°03’W, 79-82 m, 2 lv, 1 rv (3 paratypes MNHN 18°41’S, 174°02’W, 76-85 m, 1 spm (holotype MNHN 20461 ), 20463) .

4 lv, 10 rv (12 paratypes MNHN 20462, 2 HD); stn DW 1582,

DESCRIPTION. — Shell up to c. 4 mm in height, subcircular, inequivalve, nearly equilateral, right valve somewhat more convex than left, auricles nearly equal in size, semi-transparent and coloured with white spots, cardinal crura broad; with internal ribs.

Left valve sculptured with closely spaced, delicate radial lirae (12-14 per mm near ventral margin). Pre-radial stage (1 mm high) with about 10 very fine commarginal lamellae. Anterior auricle with commarginal lamellae, more prominent on disc flank, posterior smooth. Anterior and posterior auricle not distinguished from disc.

Right valve with delicate, widely and regularly spaced commarginal lirae (about 5 per mm on central part of disc) and covered with microscopic granular shell layer. Anterior auricle (folded near byssal fasciole) separated from disc by a suture, posterior continuous with disc. Anterior auricle with widely spaced commarginal lamellae (16-18), similar number of widely spaced but weaker commarginal lamellae on posterior auricle, more prominent near margin. Byssal notch small.

Prominent internal ribs (10) commencing after 0.5 mm shell height and extending nearly to ventral margin.

Dimensions of holotype: H 3.8, L 4.1, D 1.0.

REMARKS. — Similipecten herosae differs from the only related species in the Indo-Pacific, Similipecten eous (Melvill in Melvill & Standen, 1907) from the northwestern Indian Ocean (see Dijkstra & Knudsen 1998: 50), in having a different sculpture on the left valve ( S. herosae radial sculpture, S. eous some commarginal growth lines or smooth) and internal ribbing ( S. herosae has 10 ribs, which are lacking in S. eous ).

It is quite remarkable that strongly internal ribs are developed in S. herosae . Generally these are lacking in all species of Similipecten , although specimens of Similipecten similis (Laskey, 1811) from the eastern Atlantic also have auricular riblets and sometimes rudimentary internal ribs (Dijkstra unpubl. data).

Although S. herosae has internal ribs, it has no other characters in common with species of Propeamussium or Parvamussium but several characters of Similipecten (small size, subcircular shape, right valve more convex than left valve, broad cardinal crura, anterior auricle of right valve somewhat curved, commarginal sculpture of right valve lacking or very weak) and hence we place it in this genus.

S. similis

Height up to 7 mm

LV smooth or rarely commarginal striae

Internal ribs absent or rarely rudimentary

Colour highly variable

S. eous S. herosae

3 mm 4 mm

smooth radial sculpture

absent 10

whitish whitish

ETYMOLOGY. — Named after Virginie Héros, curator of molluscs in MNHN, and generous resource person for the many taxonomists working on material from French expeditions.

Genus CYCLOCHLAMYS Finlay, 1926