Lucinoma myriamae Cosel 2006, n. sp.

Lucinoma myriamae n. sp. (second morph)

(Figs 18B; 19)

MATERIAL EXAMINED. — Northern Angola. W of Ambrizete, 7°18.42’S, 12°04.60’E, 360-367 m, trawled RV Thalassa, ZAIANGO BIOL 2, stn CP 09, 29.VIII.2000,

leg. R. von Cosel, 3 sh., numerous rv. and lv. in part more or less worn (MNHN). — W of Ambrizete, 7°18.31’S, 12°04.82’E, 371-375 m, taken by ROV Victor, RV Atalante, BIOZAIRE 1, stn PL 79-3, 6.I.2001, leg. M. Sibuet, 1 sh., several v. and fragments, more or less worn (MNHN). — Same locality, 7°17.78’S, 12°02.66’E, 372- 408 m, taken by ROV Victor, RV Atalante, BIOZAIRE 1, stn PL 77-1, 5.I.2001, leg. M. Sibuet, several mostly worn v. (MNHN).

DESCRIPTION

Shell to 53 mm long, thick and solid, variable in outline, subcircular (length/height ratio between 1.0 and 1.2), inflated. Anterior margin broadly rounded, with an indistinct truncation, antero-ventral margin almost more or less rounded. Posterior margin broadly rounded-truncated, with rounded corners. Ventral margin well convex. Antero-dorsal (lunular) margin straight to slightly concave, postero-dorsal margin convex. Beaks slightly in front of the vertical midline.

Exterior with rather densely to more widely spaced commarginal lamellae and on the interspaces with numerous, strong and dense, more or less irregular commarginal cords, becoming obsolete on the very early parts of the valves which may be eroded. Anterior area delimited by a rounded anterior angle, posterior area by a rounded posterior angle and often marked by a shallow to indistinct indentation of the posterior margin. Lunule and hinge dentition as in the “normal” morph.

Measurements are provided in Table 9.

REMARKS

This “morph” is distinguished from the type series by its shorter, higher and more rounded shells with much denser commarginal lamellae. The shells are often more tumid. There are all kinds of intermediates to the “normal morph”. Lucinoma myriamae n. sp. with its two morphs shows well the plasticity of species of Lucinoma at a single locality. The nominate “morph” could be compared with Lucinoma species from the Indo-West Pacific of which one (under description by Cosel & Bouchet, unpubl. data) has the same outline and ornamentation.

A close-looking species is Lucinoma kazani Salas & Woodside, 2002, found live in the eastern Mediterranean in a cold seep area on mud volcanoes in the Anaximander Mountains at 1165-1854 m depth S of Turkey (Salas & Woodside 2002). However, L. kazani is smaller (up to 38.4 mm length), less high and has finer commarginal cords, also with strong and irregular growth lines between them (see Fig. 18C). The diverging part of the anterior adductor scar is somewhat broader and shorter as in L. kazani. The other large Atlantic species, L. borealis (Linnaeus, 1767) (northern Norway to Cap Blanc, Mauritania and throughout the Mediterranean), is more circular, slightly smaller (on the West African coast to a length of 40 mm), in average less tumid and, in contrast to L. myriamae n. sp., it has more densely spaced irregular commarginal ridges or lamellae.

An interesting fact is the similar distribution patterns of the cold seep species pairs Lucinoma kazani - L. myriamae n. sp. and Isorropodon perplexum - I. bigoti (Vesicomyidae, see Cosel & Salas 2001), of which one species lives on the seeps in the eastern Mediterranean and the other species off northern Angola.