As with other members
of Family Myidae, this species has a shelflike or spoonlike chondrophore
projecting from the hinge
plate of the left valve,
has two adductor
muscles of similar size, and no radial
ribs. Mya arenaria has a
well-developed, deep pallial
(on the left valve)
is well-developed, projecting as far or nearly as far as it is wide (photo).
to the middle (photo).
ligament is internal, attached to the chondrophore (photo).
end of the shell is less smoothly rounded than is the anterior
but it is not truncate.
slightly at each end, especially the posterior
end (photo). The shell
is brittle and chalky
white or gray outside with some light yellow or brownish periostracum
and uneven concentric rings. The siphons
are light brown with darker tips (photo).
Length to 17 cm, most often 10 cm or less in our area.
(Arenomya) arenaria Linnaeus,
Common name(s): Softshell clam, Eastern softshell clam, Mud clam, Soft
clam, Long-necked clam, Long clam, Steamer clam, Nanny nose, Sand gaper
arenaria from the beach
at Freeland, Holmes Harbor, Whidbey Island.
|(Photo by: Dave
How to Distinguish
Similar Species: Mya
truncata and Platyodon
have a truncate posterior
end and rarely exceed 7 cm. This species may be found along
horse clams such as Tresus
capax and may look like a small individual of
that species or
especially like Tresus
but the horse clams such Tresus
capax have a chondrophore
in BOTH valves
a large gape between the valves
at the posterior
AK to Elkhorn Slough, Monterey, CA; Japan, Kamchatka, North Atlantic,
and Baltic Seas
depth in San Francisco Bay is 30 cm above zero tide line)
In mud or sandy mud, sometimes
mixed with gravel. Common in estuaries and other areas of
salinity (to as low as 23% seawater).
has been introduced from the Atlantic, being first seen in San
Bay in 1874. It slowly spread north, and reached Alaska in
By the 1920's it seems to have largely displaced the native clams in
Francisco Bay. This clam has long siphons,
and can be 20-35 cm below the surface. It can live
for several days, and dissolves the shell to buffer acidity in these
In San Francisco Bay its optimal intertidal depth is 30 cm above zero
line. The siphons
appear as slits at the surface of the mud, and emit a spurt of water as
they contract if one steps near them. This clam burrows only
without using the foot much. Burrowing is by closing the valves
and forcefully ejecting water. Predators include skates,
sharks. Predators in Europe include oystercatchers and
which the clams have a refuge in depth if over 15 cm deep.
pea crab symbionts. Mature at about 2-4.5 cm, and spawn in
or summer. This species is highly esteemed for food.
and Fairbanks, 1966
and Carlton, 1975
and Brusca, 1978
et al., 1980
and O'Clair, 1998
General Notes and
abundances, unusual behaviors:
In this view of the hinge mechanism from the anterior
end of the shell, the large chondrophore
projecting from the hinge
plate of the left valve
can be seen.
The left chondrophore
attaches by the hinge
ligament (dark brown in this photo) to a socket in the right valve,
dorsal to the chondrophore.
|The large chondrophore
projecting from the left hinge can be seen here. This view is
toward the hinge
plate from inside the clam. The hinge
ligament attaches to the other side of the chondrophore.
||This view shows the left chondrophore
from the hinge plate side. This is the side the hinge
ligament attaches to. Notice the projection from
margin of the chondrophore,
which probably gives stronger attachment to the ligament
|In this view of the right hinge
plate from perpendicular to the shell, the socket in the
to which the hinge
ligament from the left chondrophore
attaches can be seen. Note that the socket angles back from
||Tipping the right valve
up so that the socket can be clearly seen shows the size of the socket.
The inside view of the clam shows the deep pallial sinus, the large
adductor muscle scars, and the arrangement of the chondrophore
socket (right valve).
is to the left in this view. The upper valve is the left valve,
the lower is the right valve.
This view of the umbo,
which is slightly anterior
to the middle of the shell, also shows that both ends, especially the posterior
end (to the right) often gape at least slightly. No hinge
ligament can be seen because it is internal and attached to
Note the chalky texture and brittleness of the shell.
in this species are brown with darker tips. These siphons
are not fully extended.
Authors and Editors of Page:
Dave Cowles (2007): Created original page
CSS coding for page developed by Jonathan Cowles (2007)