Benthonella tenella ( Jeffreys, 1869 )

Gofas, Serge, 2007, Rissoidae (Mollusca: Gastropoda) from northeast Atlantic seamounts, Journal of Natural History 41 (13 - 16), pp. 779-885 : 865-866

Benthonella tenella ( Jeffreys, 1869)

Lacuna tenella Jeffreys 1869, p 204 –205, Plate 101 Figure 7 .

Type material

Holotype (sh.) cat. no. 185475 and two paratypes (sh.) cat. no. 186455, in the United States National Museum.

Type locality

North of the Hebrides, Great Britain.

Material examined

Gorringe— Seamount 1 sta. CP30, 83 sh. (2.90×2.18 to 4.60× 3.20 mm; figured in Bouchet and Warén 1993, p 699). Josephine— Seamount 1 sta. CP50, 2 sh. (jv.). Meteor— Seamount 2 sta. DW173, 1 sh. (4.10× 2.52 mm). Hyères— Seamount 2 sta. DW185, 368 sh. (3.20×2.20 to 4.68× 2.90 mm); DW186, 36 sh. (3.56×2.26 to 4.22× 2.64 mm); DW200, 5 sh. (2.96×2.12 to 4.60× 3.40 mm); DW203, 12 sh. (9.94×1.90 to 4.06× 2.68 mm). Irving— Seamount 2 sta. DW208, 1 sh.; DW225, 4 spm. (3.90×2.35 to 4.50× 2.95 mm) and 7 sh. Cruiser— Seamount 2 sta. DW238, 1 sh.; Plato— Seamount 2 sta. DW244, 14 sh. (3.54×2.32 to 4.06× 2.78 mm); DW250, 42 sh. (2.30×1.64 to 4.14× 2.90 mm). Tyro— Seamount 2 sta. DW275, 4 sh. (3.70×2.30 to 4.56× 2.70 mm).

Remarks

This is possibly the most widespread and common gastropod in the bathyal North Atlantic and the Mediterranean ( Rex et al. 1979; Rex & Etter 1990; Bouchet & Warén 1993). Most specimens from the seamounts, like those collected around the Azores, are thin-shelled and ribbed and would correspond to subspecies B. t. fischeri Dall, 1889 if taxonomic recognition is given to this variation (see discussion in Bouchet & Warén 1993). In the lot from Plato seamount DW250 (1500 m), the smooth form (23 sh.) coexists with the ribbed one (19 sh.) without intermediates; there the smooth form is also smaller (maximum height 3.0 mm) and has more convex whorls, but has a similar protoconch. However, in this species where development is planktotrophic, the coexistence in sympatry of discrete morphs may be caused by the contribution of batches of larvae from different geographic origins, rather than reflect the existence of two different species. Therefore, this falls very short of invalidating the conclusion of Bouchet and Warén (1993) that a single species of Benthonella is involved in the North Atlantic.

Figures

Figure 7. (A–D) Alvania microstriata Hoenselaar and Goud, 1998. (A, B) Shells from Seine seamount, DE84 (450–455 m), actual size 1.57 and 1.54 mm; (C) protoconch, same shell as B; (D) microsculpture, same shell as A. (E–H) Alvania seinensis n. sp. (E, F) Holotype (sh.) from Seine seamount, DE72 (165 m), actual size 1.40 mm; (G) protoconch of the holotype; (H) microsculpture. Scale bars: 100 Mm (C, G); 50 Mm (D, H).