Tinalucina aequatorialis, Cosel, 2006

Cosel, Rudo von, 2006, Taxonomy of tropical West African bivalves. VI. Remarks on Lucinidae (Mollusca, Bivalvia), with description of six new genera and eight new species, Zoosystema 28 (4), pp. 805-851 : 814-815

Tinalucina aequatorialis n. sp.

( Figs 5 ; 6A, B )

TYPE MATERIAL. — Holotype: Equatorial Guinea, W of Bioko Island (formerly Fernando Poo), off the coast of Cameroon, 3°50’20”N, 8°21’40”E, 98 m, in silty bottom, a fresh empty shell, taken by corer, Gardline Survey 2003, stn VIO 2, 6.8 × 6.0 × 3.0 mm ( BMNH 20040254 ).

TYPE LOCALITY. — Bioko (formerly Fernando Poo), Equatorial Guinea.

ETYMOLOGY. — After Equatorial Guinea, in which the type locality is situated.

DISTRIBUTION. — Inner Gulf of Guinea, only known from the type locality and possibly restricted to the Cameroon deeper shelf and adjacent islands.

DESCRIPTION

Shell very small (holotype 6.8 mm long), rather thick and solid, equivalve, moderately inflated, subcircular but more tending to rectangular-polygonal, slightly longer than high, length/height ratio 1.1. Umbones prominent, beaks slightly in front of the vertical midline. Antero-dorsal (lunular) margin markedly concave, antero-dorsal corner narrowly rounded, well marked. Anterior margin rounded, more so on its middle part, ventral margin rounded, less convex in its middle part. Posterior margin nearly vertically truncated, with a very slight sinuosity in the middle and with broadly rounded postero-dorsal and postero-ventral corners.

Exterior somewhat irregular, with irregularly but mostly densely-spaced, shallow, commarginal lamellae and a few growth lines. Anterior angle almost absent, anterior radial depression obsolete, antero-dorsal area indistinct. Posterior angle rounded, posterior radial depression broad and well defined, ending in a very shallow indentation of the posterior margin. Lunule small, moderately narrow, slightly asymmetric, longer than broad, a little sunken; escutcheon absent, ligament deeply sunken.

Hinge plate narrow but strong, right valve with a rudimentary single cardinal tooth, an anterior

New taxa of tropical West African Lucinidae (Mollusca, Bivalvia)

lateral and vestiges of a posterior lateral. Left valve with two small cardinals, an anterior lateral and the vestiges of a posterior lateral. Anterior adductor scar rather short, with short and broad diverging part, the pallial line meeting the scar slightly above its middle. Inner margin smooth.

Valves entirely white, periostracum thin and almost colourless, eroded on large parts of the valves.

REMARKS

The only comparable species is the Indo-Pacific T. inanis n. comb. (see Fig. 6C ), which grows only slightly larger than T. aequatorialis n. gen., n. sp., up to 10 mm; it is further distinguished by the smooth middle part of the valves, however, both species share the somewhat irregular valve surface, the general shell outline, the hinge dentition and the equi-sized adductor scars. The only other very small tropical West African lucinid species, Loripes (Keletistes) legouxi (Nicklès, 1952) ( Fig. 6D ), is easily distinguished by its internal ligament and its much more tumid valves. Tinalucina aequatorialis n. gen., n. sp. was found together with juveniles of Afrolucina discontinua n. gen., n. sp. (described herein, see below) of about the same size.

Figures

FIG. 5. — Tinalucina aequatorialis n. gen., n. sp., holotype,W of Bioko Island (formerly Fernando Poo), Equatorial Guinea, off the coast of Cameroon, 3°50’20”N, 8°21’40”E, 98 m, 6.8 mm (BMNH), exterior and interior of both v., dorsal view.

FIG. 6. — Half schematic drawings of the insides of valves: A, B, Tinalucina aequatorialis n. gen., n. sp., holotype (BMNH), interior of lv.; B, interior of rv.; C, Tinalucina inanis (Prashad,1932) n. comb.,holotype (Zoologisch Museum Amsterdam),interior of lv.; D, Loripes (Keletistes) legouxi (Nicklès, 1952), Côte d’Ivoire, continental slope (no precision), dredged RV Reine Pokou, leg. Le Loeuff, interior of rv. (for comparison). Scale bars: A, B, 5 mm; C, 10 mm; D, 2.5 mm.