Shells inequilateral, delicate and fragile. Outline ovate, wedge shaped. The dorsal and ventral margins are almost parallel; posterior margin short subtruncate; anterior margin short straight. Gape occupying most of the length of the valves. Sculpture of concentric growth fine lines only, except on anterio-ventral region where few fine raised lines develop. Animal enclosed in a calcareous tube with characteristic constrictions at regular intervals.
common size :
5 mm to 12 mm in length, tube 12 x 6.5 mm.
The native G. dubia (Pennant, 1777) has a shell which covers more of the soft parts and is well rounded posteriorly; it is also usually totally embedded in the perforated substrate and, when enclosed in a tube, this tube incorporates sediment particles and lacks the constrictions.
BIOLOGY / ECOLOGY
Borer, nestling in hard substrata, immobile, unattached organisms with a suspension feeding trophic mode.
very common, mostly attached to dead shells, enclosed in calcareous capsules (see detailed photo below), with a preference to bivalves lying on the surface of sands and muds; in deep continental shelf waters (9-91 m depth).
A valve of Gastrochaena, left: in a valve of Anadara (Coll. Spada from Barash, 1961); right: once extracted.
photo: P. Pravlis