Mytilimeria nuttalli Conrad 1837

Biology/Natural History: This species is almost always embedded in compound ascidian colonies, especially Archidostoma psammion and Cystodytes lobatus. Larve appear to settle on the ascidian colony and attach by a byssus. The clam eventually becomes surrounded by the colony except for a narrow slit for the siphons. The species is a hermaphrodite but doesn't spawn eggs and sperm at the same time.

Lives in ascidian colonies

Geographical Range: Forester Island, Alaska to Isla Rondo, Baja California, Mexico

Depth Range: Low intertidal to 40 m

As a member of family Lyonsiidae, this species has 2 adductor muscle scars of similar size. It has no hinge teethand no chondrophore. The shell has no radial ribs. The umbones do not quite touch. The interior of the valves is pearly. The pallial line and pallial sinus are continuous. The tips of the siphons are not bright red. This species is fragile and nearly circular in outline or higher than long. The periostracum is translucent yellowish brown. It is usually found embedded in colonies of compound ascidians with the siphons exposed. The shell usually cracks when dried. The shell has fine concentric growth lines, and Johnson and Snook say it also has fine radiating lines. Length to 4 cm.

How to Distinguish from Similar Species: Members of most other families have hinge teeth. Other members of family Lyonsiidae such as Entodesma navicula are longer than high and do not live in ascidian colonies.