Opalescent Nudibranch (Hermissenda crassicornis)

Other Names: Thick-horned nudibranch

Description: Alien like in appearance, the opalescent nudibranch is the most commonly found species of nudibranch at Haystack Rock. They have a translucent white body with a few iridescent blue stripes. Their body is covered with tentacle like hairs called cerata. These cerata have a bright orange tip that makes this species a little easier to spot. This coloring serves as a warning to other species that they can sting. They can grow to be 80mm long At Haystack Rock the best time to look for opalescent nudibranchs is in the spring and early summer. They are often in the tide pools on the South side of Haystack or near The Needles.

Habitat: Opalescent nudibranchs range from Southern Alaska to Northern California. They live in low intertidal to subtidal zones and can be found in rocky, sandy, or eel grass habitats.

Diet: Opalescent nudibranchs have the unique adaptation to be able to eat the tentacles of sea anemones. They also may eat hydroids and bryozoans.

Tide Pool Tidbits:

• Opalescent nudibranchs are expert recyclers! When they eat creatures like anemones that have stinging cells (called nematocysts) inside them, they repurpose these cells into their own body to defend themselves from predators.

• A very territorial species, opalescent nudibranchs are known to become violent if they venture to close to each other.

• Opalescent nudibranchs have a close relative called the Southern opalescent nudibranch (Hermissenda opalescens) that until recently was thought to be the same species. This look-a-like species ranges from California to Mexico.

Reference: Biodiversity of the Central Coast, Walla Walla University