San Diego Dorid, Dianulula sandiegensis

San Diego Dorid, Dianulula sandiegensis. Underwater photographs taken in the coastal waters off Monterey, California, February 2022. Photographs and identification courtesy of Bob Hillis, Ivins, Utah.

Phylogeny:  The San Diego Dorid, Diaulula sandiegensis (J. G. Cooper, 1863), is a member of the Discodoridae family of Nudibranchs. The genus Diaulula is one of thirty genera in this family, and there are eighteen species in this genus. They are also known as the Leopard Dorid, Ringed Dorid, Ring-spotted Dorid, and Tar-Spot Dorid, and Leopard Dorid and in Mexico as  Dórido de San Diego.

Morphology: San Diego Dorid is soft-bodied gastropods that lose their shell during their larval phase. They have a thick mantle on their back (dorsal surface) that extends over the foot. Their gills are retractable, and 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. San Diego Dorids have an elongate oval outline. They may be white, yellowish-brown, or light gray in color, marked by black, or dark brown, rings and/or blotches. Other species in the area may also exhibit dark spots or blotches, but only the San Diego Dorid has doughnut-like rings. The gills and rhinophores are the same color as the body. Fine tubercles give the dorsal surface a velvety appearance and a gritty feel. These dorids are relatively solid to the touch. They reach a maximum of 12.5 cm (5.0 inches) in length.

Habitat and Distribution:  The San Diego Dorid reside on and under rocks in the intertidal zone and to depths up to 35 m (115 feet).  They are an Eastern Pacific species that have a very limited range being found along the entire west coast of Baja in the Pacific Ocean. Reports of their presence within the Sea of Cortez are inconsistent.

Diet: San Diego Dorids are spongivores, feeding on Halichrondria, Haliclona, Myxilla and Petrosia sponges.

Predators: The San Diego Dorid is poorly studied and understood species. There is very little documentation regarding their predators. Other species in this family are preyed upon by other nudibranchs.

Reproduction:  San Diego Dorids are simultaneous hermaphrodites (having both male and female reproductive organs). They reproduce sexually by hypodermic insemination. This occurs when both mating partners dart their penis toward each other to induce one to act as a male and the other as the female. The victorious one to penetrate the body wall is the dominant male. The egg ribbon is a narrow, white, oval spiral , attached by one edge, under rock ledges. The eggs hatch into veliger larva and later metamorphose into adults.

Ecosystem Interactions:  The San Diego Dorid is a poorly studied and understood species. There is no documentation regarding their involvement in commensal, parasitic, or symbiotic relationships.

Human Interactions:  San Diego Dorids 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:  Discodoris sandiegensis and Doris sandiegensis.