The Hermissenda opalescens, or Opalescent Nudibranch, is one of the many colorful nudibranchs, or sea slugs, found along the western coast of the United States and Canada ranging from Alaska all the down to Baja California in Mexico. The opalescent nudibranch gets its name from the opal colored frills on its back (that are exposed gills). 

This nudibranch has also been given the nickname the "electric" nudibranch due to its bioluminescent capabilities. When threatened, the "electric" nudibranch will flash lights from the tips of its frills from to scare off predators.

Like all nudibranchs, the opalescent nudibranch has two sensory organs called rhinophores which are used to detect prey. 

Additionally, this nudibranch is also commonly used for studies of neural and sensory systems due to its complex nervous system and sensitivity to various stimuli. 

Be on the look out for these gorgeous critters while diving on the California coast and while visiting local tide pools.