Graecina karinae, 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 : 825-828

Graecina karinae n. sp.

( Figs 12 ; 13 )

TYPE MATERIAL. — Holotype: N Angola, Angola Margin , 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, lv. ( MNHN).

Paratypes: same locality, 3 rv., 1 lv. ( MNHN) ; 2 rv. ( BMNH).

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

ETYMOLOGY. — Dedicated to my colleague Karine Olu-Le Roy from IFREMER, in acknowledgement of her longtime kind collaboration on bivalves of cold seeps.

OTHER MATERIAL EXAMINED. — Nigeria. S of Port Harcourt, 3°42.28’N, 7°47.59’W, 425 m, taken by corer, RV Le Suroît, stn GUINESS 2, 2.IX.1993, leg. P. Cochonat, 2 fossilized lv., 1 rv. (MNHN).

Northern Angola. Angola Margin, off 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, 6 lv., 9 rv., all old and partly chipped or worn ( MNHN).

DISTRIBUTION. — Nigeria; Northern Angola.

DESCRIPTION

Shell medium-sized, up to about 40 mm long, rather thick and solid, somewhat variable in outline, subcircular (length/height ratio 1.1), inequilateral, equivalve, rather compressed. Beaks well in front of the vertical midline. Anterior part broadly rounded, anterior margin evenly convex. Posterior part rounded, posterior margin convex but occasionally obliquely truncated, with rounded postero-ventral corner. Antero- and postero-dorsal margins sloping, with a curved hinge line; margin between the lunular area and the anterior margin strongly curved. Postero-dorsal margin convex, occasionally more so in its upper part behind the umbones. Ventral margin rounded, in the middle less convex.

Exterior with thin commarginal lamellae or cords, only on the earlier third or fourth or sometimes the very earliest part of the valves, becoming obsolete and then absent towards ventrally. Interspaces with very fine growth lines only. Rest of the valves with strong, dense and rather regular growth lines and some coarser “growth stages”. Antero-dorsal area with two shallow radial depressions, one closely under the lunular area, the other somewhat more below it, anterior angle indistinct. Postero-dorsal area indistinct and not separated by a visible posterior angle.

Hinge plate narrow and arched. Hinge in the right valve with one well developed cardinal tooth and sometimes the vestiges of a posterior cardinal, and long and narrow anterior and posterior laterals. Left valve with one well developed cardinal and a narrow and short anterior cardinal, and narrow, well marked anterior and posterior laterals. Lunule rather long, narrow, slightly asymmetrical, somewhat broader in the right valve, sunken. Escutcheon long, narrow and sunken, delimited by a sharp, raised and serrated keel, but no highly lamellate prolongations. Anterior adductor scar rather small, long, with moderately long diverging part, pallial line meeting the scar in about its middle or just above it. Posterior scar small but rather broad. Inner margin of valves smooth.

Valves presumably white in life but in the dead collected samples chalky or light greyish. Periostracum thin, light greenish brown, when present.

Measurements are provided in Table 5.

BIOTOPE

All collected specimens are rather aged single valves. They were trawled, together with complete shells and/or valves of two other lucinid species, also described herein (see below), on a site at the Angola shelf margin (ZAIANGO Program, site B) where about 20 to 45 m high, circular mounds of deep water coral ( Lophelia pertusa (Linnaeus, 1758)) are present ( Dekindt et al. 2001; Olu-Le Roy pers. comm.). On these mounds, living corals are on top and on the higher parts, whereas dead corals and debris are found on the lower part and at the bases. The lucinid shells and valves were on the sediment around and in depressions between the mounds. In the trawl, which had passed on an almost N-S line just at the base of coral mounds in a depth of 360-425 m, they came up as agglomerations of dead shells embedded in dark grey and very sticky mud, but none of the lucinids were collected alive or in very fresh state. Some valves had even pieces of solidified mud on them, which were difficult to remove. It is presumed that these Lucinidae species come from a site of reducing sediments where fluid emissions (methane or sulfide-rich) may still be slightly active or are no longer active, and where the fauna is dying out.

REMARKS

As for the genus.

Figures

FIG. 12. — Graecina karinae n. gen., 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, 31.8 mm (MNHN), interior, exterior and dorsal view of lv.; B, paratype 1, same locality, 36.0 mm (MNHN), exterior and interior of rv.; C, South of Port Harcourt, Nigeria, 3°42.28’N, 7°47.59’W, 425 m, RV Le Suroît, 23.1 mm, exterior and interior of rv.; D, same locality, 26 mm, exterior and interior of lv.

FIG. 13. — Graecina karinae n. gen., n. sp., half schematic drawings of the insides of valves: A, holotype, lv.; B, C, paratypes,rv. Scale bars: 10 mm.