Opalescent nudibranch (Hermissenda crassicornis)
The opalescent nudibranch (or sea slug) is a brightly colored marine gastropod mollusk. Its distribution overlaps with Hermissenda opalescens in Southern California and Mexico, but H. crassicornis extends north to Alaska. They were considered a single species until recently.
These sea slugs grow to be about 50 mm (~2 in) and vary in color depending on location. However, they can be recognized by an orange stripe along the head and white stripes on the cerata and running down the mantle.
This nudibranch prefers to feed on tunicates, but will also browse on a diverse diet of hydroids, anthozoans, crustaceans, dead animals, and jellyfish polyps. It has been known to prey on other nudibranchs, and will readily cannibalize smaller sea slugs of its own species.
We frequently see this species colonizing and laying eggs on the Shallow Profiler Mooring platforms, in ~200 meters of water off the coast of Oregon and near Axial Seamount.
References:
Wikipedia
WoRMS Taxonomic Index
