Mycale adhaerens, the purple scallop sponge, is a species of marine demosponge in the family Mycalidae.

It grows symbiotically on the valves of scallop shells and is native to the west coast of North America.

If the starfish does try to force the scallop's valves apart, the tube feet seem unable to obtain a purchase on the sponge.

Quite apart from this, the scallop will often try to escape from the starfish by swimming away, and will also try to evade the nudibranchs Doris odhneri and Peltodoris nobilis which feed on the sponge.

The sponge may also benefit from the scallop's movements, both by being transported into areas of clean water and by avoiding the accumulation of sediment.