Navanax inermis (J. G. Cooper, 1863)

Description

A large sea slug that can exceed 20 cm in length. The body is tan, dark brown, black or purplish, finely streaked all over with yellow, and the margins of the two large lateral folds are lined with iridescent blue dots and yellow-to-orange streaks. The sides of the body are expanded into large folds, and a small shell is retained internally.

Distribution

Eastern Pacific, from Monterey, California, south to Baja California, Mexico, and the Gulf of California. It occurs in habitats ranging from rocky intertidal shores to sheltered muddy and sandy bottoms. The species was originally described from California.

Etymology

The specific epithet inermis is Latin for “unarmed” or “defenceless,” referring to the animal’s lack of protective spines or armour.

Remarks

A voracious carnivore that preys on other sea slugs and snails. Rather than relying on eyesight, it follows the mucus trails of its prey (and of potential mates) using chemoreceptors. It takes bubble snails such as Bulla and Haminoea, aeolids such as Hermissenda crassicornis, and even small fish, and is also cannibalistic. When disturbed, it secretes a bright yellow substance into its trail that warns other individuals and deters predators.

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References

• Strategus inermis n.sp., Cooper J.G. (1863). On some new genera and species of California Mollusca. Proceedings of the California Academy of Natural Sciences. Series 1, 2: 202-207.
• Navanax inermis, Behrens D.W., Hermosillo A., Fletcher K. & Jensen G.C. (2022). Nudibranchs & Sea Slugs of the Eastern Pacific. Molamarine.