Sea-clown Nudibranch, Triopha catalinae

Sea-clown Nudibranch, Triopha catalinae. Underwater photograph taken in the coastal waters off Monterey, California, February 2022. Photograph and identification courtesy of Bob Hillis, Ivins, Utah.

Phylogeny: The Sea-clown Nudibranch Triopha catalinae (J. G. Cooper, 1863), is a member of the Polyceridae family of Nudibranchs. The genus Tryopha is one of twenty-six genera in this family, and there are four species in this genus. They are also known as the Catalina Triopha, the Clown Dorid, and the Sea-clown Triopha and in Mexico as Nudibranquio Payaso Marino.

Morphology: Sea-clown Nudibranchs are soft-bodied gastropods that lose their shells during their larval phase. They have a thick mantle on their back (dorsal surface). Their mantle skirt is reduced, forming a rim around the margin. Their gills consist of feathery plumes that encircle the anus. They have rhinophores (horn-like projections) on their heads. Rhinophores are chemosensory organs help them to locate food and potential mates. They lack complex eyes, but have photoreceptors that sense light and dark. Sea-clown Nudibranchs are elongate, tapering toward the tail. They are white to grayish tan in color. They have numerous orange, branching, tubercles on their dorsal surface and around the head. The tips of the rhinophores and gills are red to reddish orange. Sea-clown Nudibranchs reach a maximum of 7.0 cm (2.7 inches) in length.

Habitat and Distribution: Sea-clown Nudibranchs are found on rocks and kelp from the low intertidal zone to depths up to 80 m (262 feet). They are a Northern Pacific species that have a limited and discontinuous range being found along the west coast of the Baja Peninsula from the United States border to El Tomatal, Baja California. They are also found in the central Sea of Cortez, near Bahía de los Ángeles, Baja California.

Diet: Sea-clown Nudibranchs are specialized predators that eat several species of branching bryozoans, including:  Bugula mollis, Caulibugula ciliata, Cellaria mandibulata, Crisia spp., Dendrobeania lichenoides and Scrupocellaria spp. They ingest the crusty branches of the  bryozoan and digest the soft parts.

Predators: Sea-clown Nudibranchs are a poorly studied and understood species . There is very limited documentation of their predators. The California Cone Shell, Californiconus californicus has been observed stinging and paralyzing a Sea-clown Nudibranch, but it is unknown if it consumed it. Other species in the Polyceridae Family are usually prey for other nudibranch species.

Reproduction:  Sea-clown Nudibranchs are simultaneous hermaphrodites (having both male and female reproductive organs). Reproduction is sexual, with internal fertilization. Mating is accomplished by two individuals aligning themselves so that they lock onto each other with their gonopores (structure on their right side that is usually retracted). Both individuals become inseminated. The eggs are laid as a string-like mass and hatch into veliger larva and later metamorphose into adults.

Ecosystem Interactions:  The Sea-clown Nudibranch is a poorly studied and understood species. They are known to host juvenile Scale-worm Polychaetas from the Polynoidae Family as epibionts, but the exact nature of that relationship is unknown.

Human Interactions:  Sea-clown Nudibranchs have no direct impact on human activities. From a conservation perspective they have not been formally evaluated however they are fairly common with a relatively wide distribution and should be consider to be of Least Concern.

Synonyms: Triopa carpenteri, Triopa catalinae, Triopha elioti, and Triopha scrippsiana.