Thyasira, Lamarck, 1818

Thyasira View in CoL “ perplexa ” Ockelmann MS

Figs 5–6

In the archive, this species is represented by stipple drawings of two shells, hinge and anatomy ( Fig. 5). Drawn shells (2 valves) + 6 valves + 2 shells from Ria de Arosa, N Spain stn 1566 (all NHMD-1175772), are present. There is no correspondence relating to these shells and further information on their provenance could not be found. The Ria de Arosa is situated on the north-west coast of Spain, approximately 40 km N of Vigo. Its deepest point is 60 m and T. flexuosa has been recorded from here ( Cadee 1968).

At first, this did appear to be an undescribed species, but scanning electron microscopy of the prodissoconch revealed two morphologies, one with what I call a “menorah” sculpture of ridges ( Fig. 6G View Fig ) and the other almost smooth ( Fig. 6F View Fig ). The larger shell ( Fig. 6A View Fig ) with the “menorah” prodissoconch sculpture is not too dissimilar from T. equalis , but the serrated edge to the submarginal sulcus is unusual and may indicate that a distinct species is present in northern Spain. All the smaller shells, with a smooth prodissoconch, are similar to Axinulus alleni ( Carrozza, 1981) ( Fig. 6D–E View Fig ) and the anatomy matches that in Ockelmann’s diagram. The shell outline and anatomy here are, however, quite divergent from that illustrated by Payne & Allen (1991: figs 78–79) but are similar to that illustrated by Carrozza (1981: figs 1–3). The shell illustrated by Payne & Allen (1991) came from the Cape Basin off Angola and is probably a distinct species.