These large barnacles were growing on the bottom of an oceanographic buoy. It was a nice comparison of two local species.
Did you notice the different colors of the opercular membranes that are visible on the inside of the plates?
The right-hand barnacle, with a turquoise and red-orange membrane, is Megabalanus californicus. The left-hand barnacle, with a yellow-orange membrane, is Balanus nubilus. [Fun fact: Balanus nubilus was first described by Charles Darwin in 1854.]
Megabalanus is a more southern species, but it has become more common in this area during the past couple of warm-water years.