Oval cap-shaped shell with oval hole (about 1/10th the shell length) at apex.
Exterior rough, with numerous coarse radial ribs crossed by concentric threads,
creating a lattice effect. Apex forward of center. Edge of shell crenulate.
Shell greyish-white, often with brownish-purple rays. Interior white.
Alaska (Afognak Island) to Baja California (Camula).
On and under large rocks on rocky beaches and reefs. Sometimes found on
large kelp stems. Common at low-tide line, but also subtidal to 40ft.
Diodora aspera is omnivorous, feeding on bryozoans, sponges and algae.
It has an interesting response to predatory starfish; when confronted, it raises
itself by extending the foot and extends the mantle over the foot and edge of the
shell. This makes it more dificult for the starfish to attach. A commensal
scaleworm (Arctonoe vittata) is nearly always found in the mantle cavity.
The worm also bites the starfish, causing them to retreat.