Entodesma navicula (Adams & Reeve 1850)

How to Distinguish from Similar Species: Mytilimeria nuttalli has valves with a nearly circular outline or higher than long. Entodesma pictum has valves which do not gape, and is only up to 2.5 cm long.

Biology/Natural History: Simultaneous hermaphrodites, though fertilization is external. Animals alternately release sperm and eggs. Shell often grows to conform to the hole or crevice it is in; or if not constrained, the anterior end grows narrow and short and the posterior end is swollen but abruptly truncate and gaping. Can attach by byssal threads to its crevice. Predators include Pycnopodia helianthoides. May contain a symbiotic pea crab Pinnixa faba.

Holes and crevices in rocks; Holdfasts of kelp and giant barnacles at the lowest low tide

Geographical Range: Aleutian Islands, Alaska to Baja CA

Depth Range: Low intertidal to 20 m

This clam has a deformed-appearing shell, longer than high, with no hinge teeth nor chondrophore. Johnson and Snook say that the hinge is covered internally by "an oblong white ossicle". The shell has no radial ribs but is often covered with a golden-brown or greenish periostracum which, in this specimen, appears to be loose and baggy. If the periostracum is worn off, the outside of the valves is chalky. The valves tend to crack when dried. The inside of the valves is at least slightly pearly, and is glossy and iridescent. It has a continuous pallial line and pallial sinus. The valves gape on the posterior end, and the periostracum often extends past the shell at this point. Siphons are orange. Length may exceed 10 cm.