The right valve of the ‘echinata’ ecotype of Saccostrea
cucullata is slightly convex. External surface is eroded but
there may be between 10-30 closely spaced radial to subparallel
ribs and short, hollow, black hyote spines. Ribs not
raised; may retain thick, overlapping, dark greenish-black,
conchiolin scales. Where the conchiolin scales are eroded,
the exterior surface is either white or purplish black with white
streaks radiating from the umbone and at the margins. Shell
margin crenulate to irregularly plicate with flaky scales fitting
closely within the margin of the left valve. The right valve
of juveniles is circular, black and covered densely with short
hyote spines