Tomopleura tricincta, Gofas & Rolán, 2009

Gofas, Serge & Rolán, Emilio, 2009, A systematic review of “ Asthenotoma spiralis (Smith, 1872) ” in West Africa, with description of two new species (Mollusca, Gastropoda, Conoidea), Zoosystema 31 (1), pp. 5-16 : 13-15

Tomopleura tricincta n. sp.

( Figs 9 ; 10C ; 11C )

Asthenotoma spiralis – Ardovini & Cossignani 2004: 220 (unnumbered figure of a specimen from Gorée, Senegal, but not the specimens from Mauritania and Gabon on pages 219 and 220) [non A. spiralis ( Smith, 1872) ].

TYPE MATERIAL. — Holotype (spm, 13.7 × 4.2 mm, MNHN 21410 ) ( Fig. 9A, B ) and 8 paratypes (sh, 8.7 × 2.9, 12.2 × 3.9, 14.2 × 4.6, 18.7 × 5.5 mm) from the type locality (4 MNHN 21411 , 4 MHNS).

TYPE LOCALITY. — Cape Palmeirinhas, Angola (09°00’S, 12°59’E, 10-30 m) on sandy bottom.

ETYMOLOGY. — The name alludes to the three evenly developed cords which are seen on the first teleoconch whorls and diagnose the species.

MATERIAL EXAMINED. — Mauritania. RV N’Diago stn 188, 17°18’N, 16°13’W, 14 m, 1 spm (9.6 × 3.2 mm). — RV N’Diago stn 231, 17°42’N, 16°07’W, 17 m, 1 spm (9.8 × 3.3 mm).

Senegal. Bay of Rufisque, leg. M. Pin, 3 sh (15.2 × 4.2 to 20.9 × 5.6 mm). — Casamance, RV Louis Sauger, 12°47.2’N, 17°12.4’W, 24 m on fine sand, 1 spm (14.1 × 4.7 mm). — Dakar Bay, 30 m (10.8 × 3.8 mm, MHNS).

Ivory Coast. Abidjan area, leg. Marche-Marchad, 1 sh (6.3 × 4.7 mm) and 1 spm (13.0 × 3.9 mm).

Gabon. Port Gentil, “Anguille” oilfield, 00°47.4’S, 08°43.6’E, 25 m, leg. C. Chevallier, 4 sh (10.8 × 3.5 to 14.0 × 3.8 mm).

Angola. Off Luanda, 40-50 m, 5 sh (9.1 × 3.2 to 11.4 × 3.5 mm, MHNS). — Cape Palmeirinhas, 10-30 m, 1 spm (13.7 × 4.2 mm) and 4 sh (8.7 × 2.9, 12.2 × 3.9 mm), 14.2 × 4.6, 18.7 × 5.5 mm) [includes MNHN types]. — Idem, 20 m, 1 spm, 3 s, 2 j (7.9 × 2.8 to 13.1 × 4.1 mm) [includes MHNS types].

DESCRIPTION

Shell slender, fusiform with a high conical spire. Protoconch ( Fig. 10C ) of c. 3 ½ smooth, very slightly convex whorls; with abapically a narrow keel coincident with the suture, with diameter of nucleus 250 µm and maximum diameter 530 µm; transition to teleoconch with a few narrow riblets which start nearly axial in their adapical part, then are markedly curved to follow the contour of the “sinusigera” aperture of the larval shell.Teleoconch of 7-10 whorls, with a strong spiral sculpture.Sculpture on spire whorls starting with three subequal keels, one subsutural, one median and one overhanging the suture on the abapical part of the whorl, separated by concave furrows; sculpture continued with the keels remaining subequal on several spire whorls, and at some stage supplemented with a fourth keel on the abapical edge, partly concealed by the subsequent whorl. Later spire whorls with the median keel becoming slightly more prominent. Body whorl with several additional acute cords abapically to the main keel, decreasing in size towards the abapical end. Furrows between spirals concave, crossed by well-defined axial riblets running parallel to the growth lines.

Aperture devoid of parietal callus on the columellar side. Siphonal canal short and broadly open; adapical end of the aperture narrowing to a small notch reaching the suture. Outer lip simple, with a marked U-shaped notch situated adapically to the termination of the second keel, at a short distance from the suture, then with a convex profile as seen from one side. Colour of protoconch dark purplish on first whorls, later whitish; teleoconch of a pale ivory colour, slightly darker near abapical end.

Living animal like T. spiralissima , with the same colour pattern.

HABITAT

On shallow bottoms (10-30 m) of clean bioclastic sands, often near rocky outcrops.

REMARKS

This species is readily recognised by the configuration of three subequal spirals on early teleoconch whorls ( Fig. 10C ), whereas the other two species have one keel becoming clearly more prominent on that part of the shell. The protoconch is distinctive, being stouter (apparent portion 800 µm high instead of 930 µm in T. spiralissima , for a same maximum diameter of 530 µm) with less convex whorls than the other two species, and being conspicuously tinged with a dark purplish hue on its apical half. The teleoconch is whitish. This species is found on rather shallow bottoms of clean bioclastic sands, normally not together with the other two.

Figures

FIG. 9. — Tomopleura tricincta n.sp.:A, B, holotype (spm,height 13.7 mm),Cape Palmeirinhas,Angola,10-30 m (MNHN);C, D, paratype (sh, height 11.6 mm), same locality (MHNS); E, F, specimen from Abidjan area, Ivory Coast (height 13.0 mm, MNHN).

FIG. 10.— Compared top whorls of the three West African species of Tomopleura Casey,1904 (MNHN):A, T.spiralissima, specimen from Pointe Noire,Congo; B, T.fuscocincta n.sp.,specimen from off Ilha de Luanda,Angola,40-60 m,paratype;C, T.tricincta n.sp.,specimen from off Cape Palmeirinhas, Angola, 10-30 m, paratype. Arrows point to the protoconch/teleoconch transition. Scale bar: 1 mm.

FIG. 11. — Diagrammatic plot of the distributions of the three West African species of Tomopleura Casey,1904:T.spiralissima n. nom. (□); T. fuscocincta n. sp. (●); T. tricincta n. sp. (▲). None of the three species were found in the southern half of Angola despite extensive sampling in the appropriate habitats.