You spoke and we heard you. Earlier today we posted a very cool photo of an opalescent nudibranch taken by Donald Quintana in a tide pool in Cayucos, California. Many of you asked us for videos of the opalescent nudibranch, so here they are!
The Monterey Bay Aquarium has some cool facts about the opalescent nudibranch (scientific name: Hermissenda crassicornis), which can be found from Alaska to Baja California in waters from intertidal to 120 feet (37 m):
Opalescent nudibranchs are one of the prettiest and most colorful species of nudibranchs. Though their colors vary, they always have bright orange areas on their backs and blue lines along each side. Cerrata (fingerlike projections) on their backs are brownish yellow, with white and gold tips.
These "sea slugs" eat hydroids and anemones, which are armed with nematocysts (stinging capsules). These nematocysts don’t harm the nudibranch; in fact, the animal transfers some of its prey’s unfired nematocysts to the tips of its own cerrata, where they become part of the nudibranch's defense system. Some experts believe that nudibranchs’ gaudy colors warn predators of these potent weapons.
More cool facts:
Opalescent nudibranchs are aggressive fighters. When two of them meet head-to-head, they’re likely to lunge into a biting battle. If one meets the tail of another and gets the first bite, it usually wins the battle and consumes the loser.
Because opalescent nudibranchs live less than one year, they have to grow and reproduce quickly—they can’t lose time looking for a mate. A meeting between two or more can be a mutual mating session, since these creatures are hermaphroditic (they have both male and female sexual organs). Later, each lays an egg string in narrow coils that looks like tiny sausage links. They attach their eggs to eelgrass and algae.