Bivalves

Click on photo to enlarge. Scale line in photo equals 1cm unless otherwise specified.
* Species which are commonly encountered on the beach.

San Juan Islands, WA
Keenocardium blandum
(Gould, 1850)
Low-Rib Cockle
subtidal, 20-80m size to 5cm
central California to northern Alaska
The shell is yellowish to dark brown and
overall shell shape can be variable. The
sculpture consists of low ribs with
generally narrow interspaces. The
inner margin is shallowly crenulate.
(synonym - Clinocardium blandum, Clinocardium fucanum)

Clinocardium nuttallii (Conrad, 1837)
Nuttall's Cockle or Basket Cockle *
intertidal to 200m size to 14.6cm
southern California to northern Alaska and northern Japan to Kamtchatka
This is very common intertidally and easy to find. It lives just barely under the surface of the sand and is readily exposed at low tide. The shell is yellowish-gray to brown. It is often light in color with orange-brown speckles and streaks when young and darkens with age. The ribs are strong and rounded and the inner margin is deeply crenulate. The animal exhibits a very strong escape response to sea stars and moon snails. It can protrude it's large foot and flip itself along the sand.

Keenaea centifilosa (Carpenter, 1864)
Hundred-Line Cockle
subtidal, 30-150m northern Mexico to southern Alaska size to 25mm
This shell has a defined posterior slope with cancellate sculpture. It is separated from
the rest of the shell by a raised rib. The remainder of the shell is covered in fine,
flat riblets. The interior margin is lightly crenulate. It had once been grouped
under the Asian species, Cardium modestum, but this species is now considered distinct.

Petersburg, AK Petersburg, AK, juvenile Pribilof Islands, AK

Serripes laperousii (Deshayes, 1839)
Broad Smoothcockle
subtidal, 2-80m southeast to northern Alaska, Korea to Sea of Okhotsk size to 13.7cm
This shell can very infrequently be found at very low tides in Alaska. The shell is
thicker than Serripes groenlandicus and more elongate. The periostracum is dull
brown and the interior is white. Juveniles typically display darker chevron markings and
visible radial striations on the anterior and posterior ends. These traits tend to disappear
and the posterior end elongates with age.

Juneau, AK Pribilof Islands, AK Pribilof Islands, AK, juvenile

Serripes groenlandicus (Mohr, 1786)
Greenland Smoothcockle
intertidal to 100m size to 13cm
Puget Sound, WA to northern Alaska; Panarctic and circumboreal, extends south to Japan in the western Pacific
and ranges from Greenland to New England in the Atlantic
This shell is very rare to find intertidally. The periostracum is yellowish-brown to dark brown. The interior is white.
Juveniles typically display darker chevron markings on the shell and visible radial striations on the anterior and
posterior ends. Both of these traits tend to disappear with age.

Comparison of blandum and ciliatum

These two species can easily be
confused, especially in young
specimens. The shapes of the shells
can sometimes be identical. The blandum
has a thinner, more delicate shell and
a much less pronounced crenulate
margin. The ciliatum is usually thicker and
more inflated, with larger teeth at the hinge.
The pictured shells show their typical
appearance in Washington and southern BC. Until recently they were in the same genus.

San Juan Islands, WA
Ciliatocardium ciliatum
(Fabricius, 1780)
Hairy Cockle
subtidal, 10-150m size to 8.5cm
northern Washington to northern Alaska
and across to Siberia; circumpolar
The shell is brown with a thick
periostracum. The ribs are triangular with
wide interspaces. The inner margin is
crenulate.
(synonym - Clinocardium ciliatum, Cardium islandicum)

Family Cardiidae