Adula californiensis (Philippi 1847)

How to Distinguish from Similar Species: A. diegensis does not taper at the posterior end and attaches to rocks or pilings. A. falcata has filelike vertical striations and is not usually found north of Oregon. Lithophaga plumula has chalky encrustaceans on the posterodorsal slopes of valves, bores in limestones, and is not usually found N of California.

Biology/Natural History: Although the valves are smooth, these mussels bore mechanically in shale or soft rock with the valves. Occasionally they can be found on the surface of a rock or attached to other mussels. The bivalve Petricola carditoides may nestle in old holes made by this species. In oregon, females produce eggs from June to October. Larvae are planktonic for about 3 days.

Boring in shale and soft rock

Geographical Range: Queen Charlotte Islands, BC, Canada to San Diego, CA

Depth Range: Intertidal to 20 m

An uncommon burrowing mussel with the shell much longer than high, umbones near but not quite at anterior end, which is rounded. The shell does not get much higher anywhere than its height at the umbones. The periostracum on the posterodorsal slopes of the valves is hairy; otherwise the valves are smooth except for some circular striations from the growth rings. The valves taper gradually at the posterior end. Periostracum shiny dark brown and hairy on the posterior end; often eroded near anterior end. Interior bluish-gray. Length less than 6 cm.