The shell shape is influenced by the surface it is attached to and by other permanently attached animals. The upper valve is flat and the lower valve is cupped. The shells are dirty white with purple splotches internally. Edges of shell can be extremely sharp. Shell length to 120 mm.

Found in low intertidal to shallow subtidal throughout North Island and northern South Island. Forms dense beds on rock and mudflats, On the mud surface initially attached to small rocks and then to each other. Found in low intertidal to shallow subtidal throughout North Island and northern South Island.

Filter feeder.

NZ Marine Fishes: Paul NZ Coastal Marine Invertebrates; Vol 1