Streptopinna

Streptopinna is an Indo-Pacific genus of bivalve molluscs characterized by a roughly triangular outline. There is only one species Streptopinna saccata.

Description
No two 'Baggy Pen Shells' are alike: they grow into unexpected shapes, conforming to the shape and position of other hard structures (rocks, coral skeletons, empty shells) in their immediate environment.

Distribution
Warm waters of the tropical Indian and western Pacific oceans.

Habitat
Buried in sandy bottoms.