Lucinoma myriamae, 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 : 832-834

Lucinoma myriamae n. sp.

( Figs 17 ; 18A )

TYPE MATERIAL. — Holotype: N Angola, Angola margin, W of Ambrizete , 7°18.42’S, 12°04.60’E, 360-367 m, BIOZAIRE Program site ZB-B, trawled RV Thalassa, ZAIANGO BIOL 2, stn CP 09, 29.VIII.2000, leg. R. von Cosel, a complete shell ( MNHN).

Paratypes: same locality, 1 rv., 3 lv. ( MNHN) ; 1 rv., 1 lv. ( BMNH) .

TYPE LOCALITY. — Ambrizete, Northern Angola, tropical West Africa.

ETYMOLOGY. — Dedicated to my collegue Myriam Sibuet, principal investigator of the ZAIANGO BIOL and BIOZAIRE program and cruise leader of ZAIANGO BIOL 2, in which the author participated and in which the species was taken.

OTHER MATERIAL EXAMINED. — Nigeria. S of Port Harcourt, 3°42.28’N, 7°47.59’W, 425 m, taken by corer, RV Le Suroît, GUINESS 2, stn KG 2 N 11, 2.IX.1993,

leg. P. Cochonat, 1 sh. with “fossilized” hardened mud between valves (MNHN).

Gabon. SW of Port-Gentil, 1°35.60’S, 8°34.69’E, 410 m, boxcorer, RV Le Suroît, GUINESS 2, stn GGS 2 G10, 25.VIII.1993, leg. P. Cochonat, 1 lv. ( MNHN).

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, associated specimens: numerous rv. and lv. in part more or less worn ( MNHN). — W of Ambrizete, 7°18.38’S, 12°04.72’E, 363 m, taken by boxcorer, RV Thalassa, ZAIANGO BIOL 2, stn KGS 20, 29.VIII.2000, leg. R. von Cosel, 1 juv. lv. ( MNHN). — Same locality, 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. ( MNHN).

DISTRIBUTION. — Gulf of Guinea: Nigeria to northern Angola.

DESCRIPTION

Shell to about 53 mm long, thick and solid, somewhat variable in outline, subcircular-triangular (length/height ratio mostly 1.1), rather inflated. Anterior part tapering, anterior margin narrowly and obliquely truncated, antero-ventral margin almost straight to straight. Posterior margin broadly rounded-truncated, with rounded corners. Ventral margin convex, more so in the middle than antero- and postero-ventrally. Antero-dorsal (lunular) margin straight to slightly concave, postero-dorsal margin convex. Beaks in front of the vertical midline.

Exterior with strong, rather regularly and widely spaced commarginal lamellae which on the earlier parts of the valves are finer and closer-set and which are obsolete on the anterior area. Interspaces with numerous, densely spaced,somewhat 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 and indistinct posterior angle. Lunule rather long and broad, sunken, with rather thick layer of periostracum on it. Escutcheon long and very narrow, delimited by a sharp keel, ligament sunken.

Hinge plate strong, moderately broad, with two well developed cardinals in each valve; posterior cardinal in the left valve thinner than the others. Anterior and posterior lateral in the right valve present as strong and well distinct knobs. Left valve with two strong anterior laterals and one weaker posterior lateral. Diverging part of the anterior adductor scar long and narrow. Inner margin smooth but ventral part of the inner surface, especially between mantle line and margin, with strong radial undulations.

Valves whitish in life, periostracum rather thin and dirty brownish.

Measurements are provided in Table 8.

BIOTOPE

No live specimens found. On sticky mud near mounds of Lophelia pertusa near reducing sediments (for details see Graecina karinae n. gen., n. sp.), shells and valves found between 360- 425 m.

REMARKS

Two “morphs” of this variable species can be distinguished: the morph on which the type lot is based ( Figs 17 ; 18A ), with rounded-triangular outline, and another, higher and more rounded morph with more dense commarginal sculpture ( Figs 18B ; 19 ), which is covered separately in the next entry. All kinds of intergrades occur between these two morphs, therefore, there is no separation on species level.

Figures

FIG. 17. — Lucinoma myriamae n. sp.: A, holotype, Angola Margin, W of Ambrizete, N Angola, 7°18.42’S, 12°04.60’E, 360-367 m, trawled RV Thalassa, ZAIANGO BIOL 2, stn CP 09, leg. R. von Cosel, 29.VIII.2000, 51.2 mm (MNHN), exterior and interior view of both v., dorsal view; B, juvenile specimen, 20.5 mm, exterior of lv.; C, S of Port Harcourt, Nigeria, 3°42.28’N, 7°47.59’E, 425 m, RV Le Suroît, specimen from piston corer, in solidified mud, 42.5 mm, exterior of lv., dorsal view; D, paratype 1, 50.5 mm (MNHN), exterior of lv.

FIG. 18. — Half schematic drawings of the insides of right valves: A, B, Lucinoma myriamae n. sp.; A, holotype; B, second morph, N Angola, from type locality; C, Lucinoma kazani Salas & Woodside, 2002, Kazan Mud Volcano, Anaximander Mountains, eastern Mediterranean, holotype (MNHN) (for comparison). Scale bars: 10 mm.

FIG. 19. — Lucinoma myriamae n. sp., second morph: A, a typical specimen, 47.1 mm, interior and exterior of both v., dorsal view; B, another specimen, 47.5 mm, exterior of both v., both from type locality.