Striped Nudibranch, Armina californica

Striped Nudibranch, Armina californica. Nudibranch collected from within San Diego Bay, San Diego, California, March 2021. Collection, photographs and identification courtesy of Bob Hillis, Ivins, Utah.

Phylogeny: The Striped Nudibranch, Armina californica (J. G. Cooper, 1863), is a member of the Arminidae Family of Dorid Sea Slugs. The genus Armina is one of six genera in this family, and there are fifty-three species in this genus. They are known in Mexico as Armina.

Morphology: Striped Nudibranchs  are soft-bodied gastropods that lose their shells during their larval phase. They have an elongated oval outline and a flattened profile. They have a thick mantle on their back (dorsal surface) that extends over the foot. The gills are located in the groove between the mantle and the foot.  They have rhinophores (horn-like projections) on their heads. Rhinophores are chemosensory organs help them to locate food and potential mates. The rhinophores have vertical lamellae, are close together, and project forward from a notch at the front of the mantle. The rhinophores are retractable. They are light brown to dark brown in color, with numerous, raised, white lines running the length of the dorsal surface. These ridges are the only raised structures on the dorsum.  They reach a maximum of 7.5 cm (3 inches) in length.

Habitat and Distribution: Striped Nudibranchs are found on sand and mud bottoms, usually in areas with limited water movement, such as bays or lagoons and can be found from the lower intertidal zone to depths up to 230 m (755 feet). They are a temperate and tropical Eastern Pacific species that are found in all Mexican waters of the Pacific Ocean.

Diet: Striped Nudibranchs prey upon the Purple Sea Pansy, Renilla amethystina and the Elongate Sea Pen, Stylatula elongata.

Predators:  Striped Nudibranchs can store toxins from their prey in glands in their mantle. This makes them toxic or distasteful to many predators.  However they are preyed upon to numerous Sea Stars.

Reproduction: Striped Nudibranchs are simultaneous hermaphrodites. 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 eggs are laid as pinkish brown to brown spirals on the bottom stratum. The eggs hatch into veliger larva and later metamorphose into adults.

Ecosystem Interactions:  There is no documentation of Striped Nudibranchs engaging in any types of commensal, parasitic, or symbiotic relationships.

Human Interactions:  Striped 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: Armina columbiana, Armina digueti, Armina vancouverensis, Pleurophyllidia californica, and Pleurophyllidia vancouverensis.