Gwynia capsula

(Jeffreys, 1859)

Shell minute, ovate and globose, rounded anteriorly, longer than wide, broadest anteriorly; with a maximum length of 1.5 mm. The external surfaces are smooth save for faint concentric growth lines. It is white or yellowish in colour with large and well-spaced punctae. Dorsal valve convex, its posterior margin nearly straight. Ventral valve as deep, convex, with a slight umbo. The deltidial plates are small and do not join medianly; the pedicle foramen is relatively large and incomplete.
Brachial support rudimentary; no median septum. Lophophore circular (with an anterio-median break), attached to the dorsal mantle (G. capsula internal).

On stones and shells (often with Argyrotheca cistellula ) on the bottom, or attached to shell-fragments and inside broken serpulid tubes in shell-gravel. It has been found in the intertidal and in shallow water (till 46 metres).

Widely distributed: off the north coast of Ireland, Irish Sea and Western Approaches.