Afrolucina discontinua, 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 : 820-824

publication ID	https://doi.org/ 10.5281/zenodo.4689802
DOI	https://doi.org/10.5281/zenodo.4892974
persistent identifier	https://treatment.plazi.org/id/666D2443-3E5D-FFBD-042C-FE41B000CB91
treatment provided by	Felipe
scientific name	Afrolucina discontinua
status	sp. nov.

Treatment

Afrolucina discontinua n. sp.

( Figs 9-11 View FIG View FIG View FIG )

TYPE MATERIAL. — Holotype: Côte d’Ivoire, off Grand Bassam , 70 m, dredged RV Reine Pokou, 1977, leg. Le Loeuff ( IRD), 1 fresh sh. ( MNHN).

Paratypes: Abidjan region (no more precision), dredged RV Reine Pokou, 1965-1974, leg. Le Loeuff, 2 sh., 1 juv. sh., 2 lv. ( MNHN) ; 1 sh., 1rv. ( BMNH).

TYPE LOCALITY. — Grand Bassam, Côte d’Ivoire.

ETYMOLOGY. — This species is a good example of the several West African species with a disjunct distribution, and that is expressed in the name.

OTHER MATERIAL EXAMINED. — Senegal. Dakar, 14°43’N, 17°30’W, 205-230 m, dredged RV Gérard Tréca, 18.III.1958, leg. I. Marche-Marchad, 1 rv., 1 lv. (MNHN). — 14°51.5’N, 17°30’W, 180- 165 m, dredged RV Gérard Tréca, 18.III.1958, leg. I. Marche-Marchad, 1 rv., 2 lv., 1 fragm. (MNHN). — Baie de Gorée, 80- 250 m, dredged RV Gérard Tréca, 20.II.1956, leg. I. Marche-Marchad, 1 chipped lv. (MNHN). — S of Gorée, 95-98 m, dredged RV Gérard Tréca, 18.II.1954, leg. I. Marche-Marchad, 1 lv. (MNHN).

Liberia. Near the border to Côte d’Ivoire, 4°31.5’N, 8°31’W, 64 m, dredged RV Calypso , 20.V.1956, 1 lv., 1 rv. ( MNHN).

Côte d’Ivoire. Abidjan region (no precision), 100 m, dredged RV Reine Pokou, leg. Le Loeuff, 1 juv. v. ( MNHN). — 4°27.5’N, 7°09’W, 50 m, dredged RV La Rafale, 6.IV.1964, leg. G. Cherbonnier, 1 juv. rv. ( MNHN). — Off S. Pedro, 4°36’N, 6°33’W, 100 m, dredged RV La Rafale, 7.IV.1964, leg. G. Cherbonnier, 1 spm ( MNHN). — Off Grand Bassam, 5°04.0’N, 3°45.8’W, 64 m, dredged RV Antéa, 16.VIII.1998, leg. R. von Cosel, 1 juv. lv. ( MNHN).

Equatorial Guinea. W of Bioko Island (formerly Fernando Poo), off the coast of Cameroon, 3°50’20”N, 8°21’40”E, 98 m, in silty bottom, taken by corer, Gardline Survey 2003, stn VIO 2, 1 juv. sh. ( BMNH). — Same region, 4°01’16”N, 8°36’06”E, 70 m, taken by corer, Gardline Survey 3003, stn NEA-I, 1 juv. sh. ( BMNH). — Same region, 4°00’45”N, 8°24’15”E, 74 m, taken by corer, Gardline Survey 3003, stn BOC3FC, 1 juv. sh. ( BMNH).

Congo (Brazzaville). N’Kossa oilfield, 5°53.12’S, 11°38.30’E, 200 m, leg. L. Bigot, 23.IX.1995, 1 rv. ( MNHN).

Northern Angola. Ambrizete, 80 m, 1982-1986, leg. S. Gofas, 1 juv. rv. ( MNHN). — Ilha de Luanda, 120 m, 1982-1986, leg. S. Gofas, 1 rv., 3 lv. ( MNHN). — Off Mussulo, 90-100 m, 1982-1986, leg. S. Gofas, 1 rv. ( MNHN). — Palmeirinhas, 60-80 m, 1982-1986, leg. S. Gofas, 7 rv., 3 lv. ( MNHN).

Second morph, somewhat longer and regular commarginal lamellae:

Bénin. Off Ouidah, 6°10’N, 2°05’E, 200 m, dredged RV Léon Coursin, 22.XI.1958, leg. I. Marche-Marchad,

3 rv., 2 lv. ( MNHN).

Nigeria. Off Niger delta, 4°05’N, 5°28’E, 90-105 m, dredged RV Calypso , 26.V.1956, 1 lv. ( MNHN).

Northern Angola. Ilha de Luanda, 120 m, leg. S. Gofas, 1 lv. ( MNHN).

DISTRIBUTION. — Senegal (Dakar); Côte d’Ivoire to inner Gulf of Guinea (northern Cameroon, Bioko); northern Angola (Luanda). Not recorded from Guinea-Bissau to Liberia (border to Côte d’Ivoire) and from southern Cameroon to the Congo Republic which may indicate distribution gaps in the tropical zone proper.

DESCRIPTION

Shell 12-18 mm long, rather solid, somewhat variable in outline and sculpture, subcircular (length/height ratio 1.1), inequilateral, equivalve, compressed. Beaks just in front of the vertical midline. Anterior margin with a slight but rather sharp corner to the antero-dorsal margin. Anterodorsal margin divided into two short, concave to almost straight parts with a corner between them, the upper part comprising the lunular area. Posterior margin obliquely truncated, with rounded corners. Postero-dorsal margin slightly convex. Ventral margin well rounded.

Exterior with numerous thin, more or less denselyspaced commarginal lamellae, which are often eroded and which may be obsolete on the first umbonal 10 mm of the valve, with surface appearing smooth. Interspaces with very fine growth lines. Antero-dorsal area well separated, with denser commarginal lamellae and wrinkles and a shallow radial depression in the middle. Postero-dorsal area separated by a rounded posterior angle.

Hinge plate narrow, hinge with one small but generally distinct oblique cardinal tooth in the right valve and two in the left valve. Anterior and posterior laterals in the right valve appearing as very small and indistinct knobs, in the left valve almost obsolete. Lunule short and rather broad, markedly asymmetrical, sunken; left valve with a strong and more or less protruding lunular plate which inserts directly under the much narrower lunular plate of the right valve into a socket under and parallel to it ( Fig. 9E, F View FIG ). Anterior cardinal of the left valve partly or completely integrated into the lunular plate. Escutcheon long, narrow and sunken. Anterior adductor scar fairly small, with short ventral part separate from the pallial line, this latter meeting the scar about in its middle or just before it. Pallial line often divided into a line of close-set separate impressions ( Fig. 11B View FIG ). Inner margin of valves smooth.

Colour of valves entirely white, periostracum very thin, yellowish brown, on the earliest part of the valves thinner to obsolete.

There exists a second “morph”, of which a few valves were collected off Bénin, Nigeria and off northern Angola ( Fig. 10 View FIG ). The valves have regular and rather densely spaced commarginal lamellae over the whole valve surface and are occasionally slightly more elongate. As very little material is available, and as there might be intergrades to the “normal” form, I leave them as a variety within A. discontinua n. gen., n. sp.

Measurements are provided in Table 4.

BIOTOPE

In soft sediment, most probably fine muddy sand, from 50 to about 230 m.

REMARKS

In outline, this species resembles somehow Graecina karinae n. gen., n. sp. (see next entry) but is easily distinguished by the sharp antero-dorsal corner, the obliquely truncated posterior margin, the sculpture, the often interrupted pallial line and the smaller size.

The distributional range of Afrolucina discontinua n. gen., n. sp. coincides with the different zones of seasonal upwelling on the coast of tropical West Africa: Senegal in the Northern zone of Alternance (see Intés & Le Loeuff 1984; Le Loeuff 1993; Le Loeuff & Cosel 1998) with strong upwelling during northern winter, Côte d’Ivoire and Bénin in the central atypical tropical zone with intermittent seasonal upwelling and Angola in the Southern zone of Alternance with upwelling in southern winter. The species seems not to be present in the northern ( Guinea to Liberia) and southern (southern Cameroon to Gabon) typical tropical zones and also not in the zones with weaker upwelling adjacent to the zones of Alternance ( Guinea-Bissau in the North and Congo in the South). However, recently a few very small specimens were found west of Bioko ( Fernando Poo), which is already in the southern typical tropical zone and within the influence of the Niger delta. The species may need some regular influence of upwelling.