Onchidoris bilamellata, 1767
This intriguing slug is one of the non-sponge-feeding dorids. It eats barnacles, which is no mean feat, considering that barnacles (as described by our buddy Chuck Darwin) have all sorts of calcareous defensive structures to protect themselves from predation. But you know how evolution works. Evolve a defense, and sooner of later some predator will come along and evolve a way to get you anyway!!
The photograph shows the animal among its prey barnacles. The white splotches are yesterdays' meals, the intact "volcano plugs" are tomorrows'!
Onchidoris bilamellata has a dirty white ground color on its dorsum, with splashes of brown covering the basic coloration.
Its range in the eastern Pacific is from Alaska, to USA, to Cabo Colnett, Baja California, Mexico. It also occurs in the eastern and western Atlantic basins. This is termed a circumboreal distribution pattern (literally, around the northern latitudes).
Photograph taken at Hat Island, Washington in June 1995.
Photos and text by Dr. Hans Bertsch