Knobby Sea Slug, Doriopsilla janaina

Knobby Sea Slug, Doriopsilla Janaina. Underwater photograph taken in Zihuantanejo Bay, Guerrero, February 2026. Photograph courtesy of Ron Woheau, Zihuantanejo.

Phylogeny: The Knobby Sea Slug, Doriopsilla janaina (Marcus & Marcus, 1967), is a member of the Dendrodorididae Family of Nudibranchs. The Doriopsilla Genus is one of two genera in the Dendrodorididae Family, and there are twenty-eight species in the Doriopsilla Genus. They are known in Mexico as Dórido Bultoso.

Morphology: The Knobby Sea Slug has an oval flat body that is cryptically colored and difficult to locate in its native environment. Their background color can vary from a deep orange to a translucent clear with visible white patches. The mantle is covered with small blackish spots and relatively large, rounded tubercles. The tubercles are often capped with deep orange, and the largest ones can be white. They are relatively small nudibranch reach a maximum of 3.0 cm (1.2 inches) in length.

Habitat and Distribution: The Knobby Sea Slug are found on mud or sand bottoms from the lower intertidal zone to depths of 20 m (70 feet). The Knobby Sea Slug is found in all Mexican waters of the Pacific Ocean with the exception that they are absent from along the west coast of the Baja Peninsula.

Diet: The diet of the Knobby Sea Slug has not been formally documented.  Most likely they consume anemones, hydroids, and nemateran worms.

Predators: The Knobby Sea Slug utilizing their swimming abilities and natural product toxin tipped cerata to avoid predation by crabs, fish and sea stars.

Reproduction: The Knobby Sea Slug are simultaneous hermaphrodites (having both male and female reproductive organs). They reproduce sexually. Copulation requires two individuals to face opposite directions, with their right sides touching. They pass sperm packets through a tube called the copulatory apparatus. After being fertilized internally, the eggs are bright orange and highly visible.

Ecosystem Interactions: The commensal, parasitic and symbiotic relationships of the Knobby Sea Slug has not been documented.

Human Interactions: The Knobby Sea Slug is known to contain the natural product Olepuapane which has been used as a natural insecticide. From a conservation perspective they have not been formally evaluated, however they are fairly common in some locations and with a relatively wide distribution should be consider to be of Least Concern.

Synonyms: None