Rock Scallop
Crassodoma gigantea

Physical Description

  • Have a thick, round, ribbed shell with many spines
  • Shells often covered in plant, animal, and algae growth
  • Mantle (scallop body seen at edge of shell) is bright orange with black eyes and sensory tentacles running along it
  • Up to 10 inches in diameter as adults
  • Juvenile rock scallops are unattached to a substrate and swim by clapping their valves together and squirting water out the sides of the hinge
  • Permanently attached to hard substrate as adults; they settle and cement themselves at about 1 inch in diameter


  • From northern Alaska to northern Mexico


  • Live in intertidal (area of shoreline covered at high tide and uncovered at low tide) and subtidal (below the low-tide line) waters along exposed outer coasts
  • Found under rocks and in crevices
  • Found at depths of 0-252 feet


  • Reproduce by broadcast spawning, releasing sperm and eggs into the water
  • Spawn twice a year in Southern California, once in late spring-early summer, and again in mid-fall


  • Rock scallops are suspension feeders who filter particulates and plankton out of the water


  • Lobsters, crabs, sea stars, fishes
  • Traditional food of coastal First Nations people

Interesting Facts

  • Rock scallops are the heaviest and the second-largest scallop species.
  • They are sometimes called the purple-hinged rock scallop because the interior of their hinges are purple.
  • Unlike all other scallops, rock scallops cement themselves down permanently to a hard surface once they reach maturity (about an inch across).
  • These scallops can live for up to 20 years.

Sources:; Macdonald et al. 1991;, UMass; Catalina Island Marine Institute; Oregon Department of Fish and Wildlife; Oregon Coast Aquarium; California Department of Fish and Game

Photo: Kevin Lee

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