Image of Marsenina stearnsii (Dall 1871)

Description:

Three Marsenina stearnsi (Stearn's Ear Shell) were found in the shallow intertidal zone on a rock face nowhere near the compound tunicate they feed on. Rather than being camouflaged and difficult to see, they stood out. They were also larger than has been noted by previous observers, being slightly over 1 inch (2.5 cm). I thought this was a sea slug at first, but noticed that tiny barnacles were living on the back of one, suggesting a shell was present beneath its white, pored mantle.