Anodontia (Afrophysema) chevalieri Cosel, 2005

Anodontia (Afrophysema) chevalieri Cosel in Taylor & Glover, 2005

( Figs 20 View FIG ; 21A, B View FIG )

Anodontia (Afrophysema) chevalieri Cosel in Taylor & Glover, 2005: 308, figs 10A, 12A, 24E-H, 25.

TYPE MATERIAL. — Holotype: Gabon, Port-Gentil, Banc du Prince, 0°36.1’S, 8°48.1’E, 5-9 m, a complete shell ( MNHN). GoogleMaps

Paratypes: same locality, 1980-1989, leg. C. Chevalier, 3 sh. ( MNHN) ; 1 sh. ( BMNH 20040252 ) .

TYPE LOCALITY. — Port-Gentil, Banc du Prince, a shoal ENE of Cap Lopez, Mandji Peninsula, Gabon.

OTHER MATERIAL EXAMINED. — Côte d’Ivoire. Continental shelf in Abidjan region (no details), trawled RV Reine Pokou, 1975-1977, leg. P. Le Loeuff, 4 sh., 1 juv. sh., 1 lv. ( MNHN).

Benin. Ouidah [Wydah], 6°10’N, 2°05’E, 200 m, dredged RV Léon Coursin, leg I. Marche-Marchad, 1 rv. ( MNHN). — 6°05’N, 2°15’E, 180-320 m, trawled RV Thierry, Guinean Trawling Survey, stn 35/7, leg. G. Cherbonnier, 4.X.1963, 1 rv., 2 lv. ( MNHN).

Gabon. Port-Gentil, Banc du Prince, 0°36.1’S, 8°48.1’E, 5-9 m, 1980-1989, leg. C. Chevalier, 7 associated specimens (sh.) ( MNHN).

DISTRIBUTION. — Only known from Côte d’Ivoire, Bénin and Gabon.

DESCRIPTION

Shell to 42 mm long, rather thin but solid, equivalve, inequilateral, very inflated, quite-variable in outline, more or less longer than high, subcircular to short-ovoid, length/height ratio 1.1. Umbones prominent, well protruding over the dorsal margin, directed forward, beaks well in front of the vertical midline. Anterior part short, anterior margin with a rather broadly rounded antero-dorsal corner, towards ventrally convex. Ventral margin well rounded and evenly convex. Posterior part broad, posterior margin well rounded, postero-dorsal corner indistinct, no postero-ventral corner.

Exterior without regular sculpture and only with coarse and very irregular growth lines and wrinkles and more pronounced growth stages. A few shallow, very broad and indistinct radial waves are also visible, especially under certain angle of view. Anterior and posterior angle absent. Lunule small and short, more or less narrow, almost symmetric, not sunken; escutcheon absent.

Ligament moderately long, broad, partly hidden by the postero-dorsal margin but not very deep sunken, on a broad nymph, which is obliquely, nearly “vertically” tilted towards the interior of the valves; therefore ligament and hinge plate appearing narrow at a horizontal view of the valve inside, full width of the ligament only visible from ventrally. In smaller specimens, ligament may be less broad.

Hinge plate very narrow and toothless. Anterior adductor scar small, with a rather narrow diverging part, the pallial line meeting the scar above its middle, occasionally at one third the length of the scar. Posterior adductor scar very small. Anterior, ventral and posterior margin on the inner side slightly, irregularly and very finely dentate, but on the very edge smooth.

Valves pure white. Periostracum very thin, pale straw coloured and mostly eroded.

Measurements are provided in Table 10.

BIOTOPE

In muddy-sandy bottom on the deeper shelf, apparently only in the Port-Gentil region of Gabon occurring shallower, from about 5 m downwards. REMARKS

This species is characterized by its very inflated shell, the broad ligamental nymph which is slanting towards the interior of the valve and the slightly dentate inner margin. A similar and possibly sibling species is Anodontia eutornus ( Tomlin, 1921) from the Indian Ocean coast of South Africa, SE Africa and SE Madagascar, described as Cryptodon eutornus by Tomlin (1921: 215, pl. 8, fig. 5). It has the same typical ovoid shell form and exceptional tumidity as Anodontia chevalieri but is still larger. Although that species had been well recognized by Barnard (1950: 181, pl. 28, fig. 5) with a figure of a typical specimen, in more recent works on South African molluscs, it was always mistaken for or synonymized with A. edentula (Linnaeus, 1758) ( Barnard 1964; Kilburn & Rippey 1982; Steyn & Lussi 1998). This is additional evidence for the close affinity of the West African marine molluscan fauna with the Indo-Pacific, especially with the Indian Ocean. For further details, see Taylor & Glover (2005).