Oyster species of the sub tropical coast of Pakistan (northern Arabian Sea)

In the present study 9 species of oysters belonging to three genera (Crassostrea, Saccostrea and Ostrea) were identified on the basis of their conchological and malacological features. These included Crassostrea gryphoides, C. madrasensis, C. belcheri, C. glomerata, Saccostrea cucullata, S echinata, Ostrea nothades, O. folium and O. cristagalli. Two species Ostrea noinades and O. cristagalli which are being reported for the first time from Pakistan. Crassostrea gryphoides and C. rivularis from Hub River Delta were earlier treated as separate species have been assigned to a single species C. gryphoides. Crassostrea gryphoides and C. madrasensis, which occur in the same habitat and show marked similarity in their external shell morphology, but differ in the colouration of their adductor muscle scar, are treated here as separate species.