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.
References:
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
A Crassodoma gigantea attached to a rock.
Photo by Dave
Cowles, July 2006
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 |