An uncommon burrowing mussel
with the shell much longer than high, umbones near but not quite at
end, which is rounded. The shell does not get much higher
than its height at the umbones. The periostracum on the
slopes of the valves is hairy; otherwise the valves are smooth except
some circular striations from the growth rings. The valves
gradually at the posterior end. Periostracum shiny dark brown
hairy on the posterior end; often eroded near anterior end.
Length less than 6 cm.
Adula californiensis (Philippi, 1847)
Common name(s): California
datemussel, California pea-pod
borer, pea pod borer
|Adula californiensis from Kalaloch,
WA. Burrowing into
shale. Scale = mm
|(Photo by: Dave Cowles,
How to Distinguish from
diegensis does not taper at the posterior end and attaches to
or pilings. A. falcata has filelike
vertical striations and
is not usually found north of Oregon. Lithophaga
chalky encrustaceans on the posterodorsal slopes of valves, bores in
and is not usually found N of California.
Islands, BC, Canada to San Diego, CA
Intertidal to 20 m
Boring in shale and soft rock
the valves are smooth, these mussels bore mechanically in shale or soft
rock with the valves. Occasionally they can be found on the
of a rock or attached to other mussels. The bivalve Petricola
carditoides may nestle in old holes made by this
oregon, females produce eggs from June to October. Larvae are
for about 3 days.
and Carlton, 1975
et al., 1980
This site by Atsushi Chiyoda discusses the biology and fossil record of boring bivalves in Japan.
General Notes and
Observations: Locations, abundances,
Most of the individuals of this species that I have
been very small--on the order of 1 cm or less long. Often
so deeply in the rock that they cannot be seen without breaking the
The inside of this mussel is a pearly blue-white or blue-gray.
This small individual was boring into soft sandstone at Toleak Point,
WA (on the open coast). Scale is millimeters, with
A dorsal view of the same individual. The dorsal margin of
shell appears slightly inflated in most individuals.
Here is an individual, also from Toleak Point, in situ inside a
Note how the dorsal margin (facing the camera) appears inflated beyond
the hinge (which is hidden between the inflated valves)
Authors and Editors of Page:
Dave Cowles (2005): Created original page