Shaggy Mouse Nudibranchs (Aeolidia loui)

Description: The shaggy mouse nudibranch may also be referred to as the California shag-rug nudibranch, mossy nudibranch, or the common grey sea slug. True to their name, shaggy mouse are covered in two dense rows of cerata that give them a fuzzy appearance. Shaggy mouse nudibranchs have two horn like protrusions on their head called rhinophores. Nudibranchs use these structures to sense their surroundings and find food. Shaggy mouse nudibranchs can come in several color morphs that range from a dark gray or brown to a light beige. Commonly around 5 cm long, shaggy mouse nudibranchs can grow up to 10 cm.

Habitat: Ranging from British Columbia, Canada to Mexico, shaggy mouse nudibranchs live in mid intertidal and subtidal habitats. Although this species is common at Haystack Rock, they are difficult to find. Often blending into the sand or rocks, shaggy mouse nudibranchs prefer areas near their food source: anemones. The best place to look for shaggy mouse nudibranchs is on boulders in low intertidal areas.

Diet: Like the thick-horned nudibranch, shaggy mouse nudibranchs feed on sea anemones and occasionally hydroids or sea pens.

Tide Pool Tidbits:

• Shaggy mouse nudibranchs have been known to eat as much as half or all of their own body weight everyday.

• Unable to digest the nematocysts in the sea anemones they eat, shaggy mouse nudibranchs re-absorb these stinging cells and store them in their cerata as a form of self defense.

• Some anemones have symbiotic algae growing within their tenticles. When shaggy mouse eat these tentacles, the algae has the opportunity to change hosts and begin growing within the nudibranch.

References: Walla Walla University, The New Beachcomber’s Guide to the Pacific Northwest by J Duane Sept