Crassodoma gigantea (Gray, 1825)

Common name(s): Giant rock scallop, Rock scallop, Purple-hinged rock scallop

Synonyms:  Hinnites giganteus, Hinnites multirugosus, Chlamys gigantea
Phylum Mollusca
 Class Bivalvia
  Subclass Pteriomorphia
   Order Ostreoida
    Suborder Pectinina
     Family Pectinidae
Crassodoma gigantea from near Northwest Island in Rosario Bay.  Length 12 cm
(Photo by: Dave Cowles, July 2005)
Description:  This large, attached scallop has anterior and posterior extensions or "wings" next to the hinge (may not be obvious), and have radial ridges running from the umbo toward the ventral margin (these may be interrupted or partly obliterated over much of the shell by uneven lumps and encrusting species).  The ridges on young specimens are prominent.  Those on older specimens often have spiny projections.  The valves are thick, almost circular in outline but their height tends to be greater than their length.  The right valve is permanently cemented to the substrate such as a rock.  The anterior and posterioradductor muscles are united into a single muscle, which leaves a single scar inside the shell (photo).  In living, open specimens a row of eyes is visible along the edge of the mantle (photo), which is orange.  There is a purple blotch near the hinge on the inside of both valves, which are otherwise white inside (photo).  Diameter to 25 cm.  One other scallop species in the world gets larger, but because of the thick shell this species is the world's heaviest species of scallop.  Freeliving juveniles have white to orange shells.

How to Distinguish from Similar Species:  Oysters such as Crassostrea gigas may be cemented to rocks but do not have the "wing" extensions near the hinge, nor the radial ridges.  Other scallop species such as Chlamys hastata are not permanently cemented to the rock.  The purple blotch on the inside of the shell near the hinge is distinctive for this species.

Geographical Range:  Prince William Sound, AK to Punta Abreojos, Baja California, Mexico

Depth Range:  Low intertidal to 78 m

Habitat:  On rocky substrates in areas of strong current and the exposed outer coast

Biology/Natural History:  This species sometimes claps its valve shut with a loud "snap", plainly audible in the intertidal zone.  Juveniles (up to nearly 5 cm) are not yet attached.  It takes them about 6 months to grow to this size.  Predators include the seastar Pisaster ochraceous and humans.  The shells are often infested with boring sponges such as Cliona celata (photo) and with tubedwelling polychaetes, bryozoans, or coralline algae.  These scallops were used for food by native Americans, and the shells were used as pendants, lip plugs, and nose rings, and in making facial and mask paint, totems, and images on canoes.  Is sometimes a protandrichermaphrodite (males when small but later become females).  Females are usually larger and more abundant than males.  The testis is white, and the ovary is red.  In Puget Sound the species spawns mid-May to mid-June, with some spawning in September.  The larvae (veligers) are planktonic for 2 months.  May live 50 years, but has been depleted from some areas due to human harvesting.

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Dichotomous Keys:
  Flora and Fairbanks, 1966 (as Hinnites multirugosus)
  Kozloff 1987, 1996  (as Hinnites giganteus)
  Smith and Carlton, 1975 (as Hinnites giganteus)

General References:
  Brusca and Brusca, 1978
  Harbo, 1997
  Harbo, 1999
  Gotshall, 1994
  Johnson and Snook, 1955
  Kozloff, 1993
  McConnaughey and McConnaughey, 1985
  Morris, 1966
  Morris et al., 1980
  O'Clair and O'Clair, 1998
  Ricketts et al., 1985
  Sept, 1999

Scientific Articles:

Web sites:

General Notes and Observations:  Locations, abundances, unusual behaviors:

The eyes can be seen along the margin of the mantle when the shell is open

In intertidal
A Crassodoma gigantea attached to a rock.  Photo by Dave Cowles, July 2006 

Old large one
This old, large individual was collected about 1900 and held for many years in the museum at Washington State University. It measures 21 cm in length. The left valve is on the left and the right valve, which is attached to a rock in life, is on the right.  Note the prominent, single adductor muscle scar, the well-marked pallial line, and the bright purple stain at the hinge. The hinge ligament is narrow but tough, and the 'wings' on each side of the hinge are not prominent. The external shell has been perforated by a boring sponge and also has a polychaete worm tube attached..

Authors and Editors of Page:
Dave Cowles (2005):  Created original page