Shell large, strong but chalky, inequivalve with lv generally smaller. Outline ovate-elongate; anterior end rounded; posterior slightly pointed. Gapes at both ends. Rough sculpture marked by concentic lines (growth lines). Distinctive hinge with an erect spoon-like tooth (chondrophore) located under the beak in left valve. Pallial sinus deep, reaching to the middle of the shell.
chalky white shell with thin greyish/brownish periostracum. Interior of shell brown.
common size :
to 152 mm in length, to 60 mm in height.
The large projecting chondrophore in lv distinguishes it from any of the otter shells (Lutraria). Similar to M. truncata Linnaeus, 1758 but bigger and more ovate. M arenaria gapes at both ends whereas M. truncata gapes widely at the posterior and hardly at the anterior edge.
BIOLOGY / ECOLOGY
Great adaptability and tolerance to low salinities and pollution. It lives buried as much as 20 cm deep in mud and sand, extending only its long siphon to the water. It rapidly retracts its siphon below the surface, if disturbed, and ejects a stream of water. Experiments on habitat selection and adult-larvae interactions in settling larvae showed that settlement was highest at a sheltered than at an exposed site (Snelgrove et al., 1999).
muddy, sandy and gravelly bottoms, intertidal from the shore and estuaries mainly in shallow water down to 75 m. Highest densities in muddy sand areas.