Tomopleura spiralissima, Gofas & Rolan, 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 : 7-11

Tomopleura spiralissima n. nom. ( Figs 2-6 ; 10A ; 11A )

Pleurotoma spiralis Smith, 1872: 731 , pl. 75 fig. 8 [non Pleurotoma spiralis M. de Serres, 1829: 261 ].

Pleurotoma spiralis – Dautzenberg 1912: 11 (the material examined from Mission Gruvel).

Asthenotoma spiralis – Knudsen 1956: 100, pl. 4 fig. 8. — Bernard 1984: 103, 106, pl. 51 fig. 211. — Ardovini & Cossignani 2004: 220, unnumbered figure of a specimen from Gabon (but not the specimens from Mauritania and Senegal on pages 219 and 220).

TYPE MATERIAL. — One syntype (Natural History Museum, London, BMNH 1871-1.24.35) ( Fig. 2 ).

TYPE LOCALITY. — Whidah, Dahomey (current names are Ouidah, Benin).

ETYMOLOGY. — The name is construed as a superlative of the preoccupied name spiralis .

MATERIAL EXAMINED. — Senegal. No further details, 1 sh (13.5 × 4.2 mm, old collection MNHN). — Off Cap Skirring, 12°25’N, 17°17’W, fine sand and rocks 25 m, 27.III.1988, leg. R. von Cosel, 1 sh (14.0 × 4.0 mm).

Guinea. Îles de Los, 5 sh (8.3 × 2.6 to 11.4 × 3 mm).

Ivory Coast. Abidjan area, 15 m, leg. Le Loeuff, 1 sh (11.3 × 3.6 mm). — Abidjan area, leg. Marche-Marchad, 1 sh (14.2 × 4.3 mm).

Ghana. Miamia , 04°50.1’N, 02°13’W, 10-20 m, 40 sh (8.3 × 2.8 to 13.1 × 4.4 mm, MHNS). — Miamia, 15-25 m, 3 spm, 5 j (6.8 × 1.9 to 11.4 × 3.9 mm, MHNS). — Princess Town, 04°47.0’N, 02°07.5’W, 10-15 m, 25 sh (8.2 × 2.8 to 13.3 × 3.6 mm, MHNS). — Mudrachmi Bay, 04°48.3’N, 02°10.3’W, 20 m, 3 spm (7.9 × 2.5 to 15.1 × 4.0 mm, MHNS) ; all specimens from Ghana collected by Peter Ryall.

Benin. The type specimen.

Nigeria. Off Niger delta, Calypso stn 24, 04°03’N, 06°12’E, 32 m, 1 sh (11.0 × 3.2 mm).

Cameroon. Victoria (currently Limbe), 03°56’N, 09°06’E, 1-3 m, 1 sh (8.5 × 2.9 mm).

Gabon. Cap Esterias, low tide, 2 sh (12.2 × 4.3, 14.2 × 4.3 mm). — Port Gentil, “Anguille” oilfield, 00°47.4’S, 08°43.6’E, 25 m, leg. C. Chevallier, 22 sh (6.8 × 2.2 to 16.4 × 5.0 mm).

Congo. Pointe Noire, beach facing ORSTOM, 3-4 m, leg. R. von Cosel, 4 sh (13.3 × 3.7 to 24.7 × 7.3 mm). — Idem, 5-7 m, 3 spm (16.2 × 4.6 to 22.6 × 6.5 mm), 2 sh (18.6 × 5.8, 21.4 × 6.8 mm). — Pointe Noire, leg. Office Pointe Noire, 3 spm (8.8 × 2.8 to 10.3 × 3.3 mm), 6 sh (up to 7.8 × 2.6 mm). — Conkouati, 04°10’S, 11°15’E, 19 m, XII.1985, leg. R. von Cosel, 1 spm (12.5 × 3.8 mm). — Songolo, 04°45’S, 11°50’E, 4 spm (13.1 × 4.2 to 17.0 × 4.9 mm), 7 sh (12.3 × 3.6 to 18.7 × 6.5 mm).

Angola. Between Shark Point and Ponta do Padrão, mouth of the River Zaire, 25 m, 4. V.1910, leg. Gruvel, 3 spm (5.8 × 2.2 to 10.2 × 3.2 mm), 9 sh (4.8 × 1.8 to 13.1 × 4.0 mm). — Barra do Dande, 08°28.0’S, 13°23.0’E, dredging 0-2 m on muddy sand, 2 sh (17.0 × 5.9, 19.3 × 6.4 mm). — Cacuaco, 08°45.0’S, 13°21.0’E, dredging 10-12 m on silty mud, 2 spm (10.5 × 3.4, 18.2 × 5.5 mm), 1 sh (14.3 × 4.9 mm). — Idem, 5-10 m, 9 spm (11.2 × 3.5 to 22.0 × 7.1 mm, MHNS). — Farol das Lagostas, 08°45’S, 13°18’E, 1 sh (13.1 × 4.3 mm, MHNS).

DESCRIPTION

Shell slender, fusiform with a high conical spire. Protoconch ( Fig. 10A ) of c. 4 smooth, moderately convex whorls, with diameter of nucleus 210 µm and maximum diameter 530 µm; transition to teleoconch with a few, broadly spaced, 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 6-9 whorls, with a strong spiral sculpture. Sculpture on spire whorls starting with one subsutural keel and another stronger keel on the abapical part of the first whorl, separated by a concave depression; sculpture continued on later spire whorls with the stronger keel shifting towards the median part of the whorls, and a third keel on the abapical edge, partly concealed by the subsequent whorl. 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 tenuous axial raised threads 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 major keel, at a short distance from the suture, then with a convex profile as seen from one side. Colour of shell dark brown, either uniform or with paler spiral keel and cords; columella dark brown, darker than surrounding areas of last whorl and aperture.

Living animal ( Fig. 4 ): foot broad and relatively short, truncated anteriorly, making a very blunt angle posteriorly, rather flat, devoid of operculum and forming a plug on the aperture when the animal is retracted. Head broad, with cephalic tentacles situated on each side of the mouth, with eyes situated at their tip; mouth quite large, appearing as a vertical slit when proboscis is retracted. Siphon quite large, tapering. Colour whitish with minute opaque white flecks on the siphon, on the head and to a lesser extent on the upper part of foot.

Radula toxoglossate, tooth slender with lancetshaped distal end and a thickened rim surrounding its base ( Fig. 5 ).

HABITAT

On soft bottoms of muddy sand or mud, usually in murky waters at 1-20 m depth.

REMARKS

Smith’s name for this species is a primary homonym of an older name used for a Miocene species of Europe, for which reason a replacement name is here proposed.

The type specimen of “ Pleurotoma ” spiralis is a rather small shell (9.5 mm) but some specimens collected in Congo and Angola reach nearly three times this size. We once considered the possibility that these larger specimens ( Fig. 3E, F ) could belong to a distinct species, supported by the observation that larger specimens tend to have spiral cords and keels paler than the general background whereas smaller forms and the holotype are uniformly brown in colour; moreover both forms were collected sympatrically at Cacuaco, Angola, and observed alive with more diffuse, coalescent whitish flecks on the large form. Nevertheless, pooling all specimens in this study ( Fig. 6 ) shows that the distribution of sizes is not bimodal and examination of the rather large lot from off Songolo, Congo, with an array of intermediate sizes and colours, has driven us to doubt about arguments for two species.

The protoconch of this species is clearly distinct from those of the two following species, being more pointed (diameter of nucleus 210 µm instead of 250 µm), slightly larger and lacking a suprasutural thread.

There is some resemblance between this species and Tomopleura fultoni (Sowerby, 1888) , a species found along the East Coast of South Africa. The latter is larger, has less conspicuous axial threads, and has only one spiral keel apparent on spire whorls; moreover the spiral keels are whitish and contrast over the dark brown background.

Figures

FIG. 2. — Pleurotoma spiralis Smith, 1872, single syntype from Ouidah, Benin (height 9.5 mm, BMNH).

FIG. 3.— Tomopleura spiralissima n.nom.:A, B, specimen from off Songolo,Congo(height 15.8 mm,MNHN),from a lot of 11 spm with sh up to 18.7 mm in size;C, D, specimen from Conkouati,Congo (height 12.3 mm, MNHN) resembling the type;E, F, large specimen from Pointe Noire, Congo (height 20.7 mm, MNHN);G-L, colour variations from Miamia,Ghana (height 14.2 mm, 14.5 mm and 11.2 mm, MHNS).

FIG. 4. — Tomopleura spiralissima n. nom. (the large form) living animal from off Cacuaco (height of shell 18 mm).

FIG. 5. — Tomopleura spiralissima n. nom.: A, single tooth of the radula of a specimen from Cacuaco,Angola (size of shell 10.4 mm); B, detail of distal end. Scale bars: A, 100 μm; B, 10 μm.

FIG. 6. — Plot of height/breadth measurements for all examined specimens and shells of Tomopleura spiralissima n. nom.

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.