Navanax inermis
(Cooper, 1863)

Family: Aglajidae


From Monterey Bay, California to Laguna Manuela, Mexico. Also throughout the Gulf of Mexico.


Big Fisherman Cove, Wrigley Institute, Catalina Island, Los Angeles County, California, USA. 26-27 May 2001, 5-8 m depth. Photo: Daniel Geiger

Navanax inermis is probably the largest aglajid growing to at least 22cm in length. It is dark brown to black with a pattern of cream to yellow longitudinal lines, sometimes broken, and sometimes replaed by a close pattern of spots. The parapodia have an orange line along the edge, and an inner line of bright blue spots or dashes. The pallial lobes at the back of the posterior shield are relatively large and taper to a point.

In nature, Navanax inermis feeds on other sea slugs - such as bubble shells and sometimes nudibranchs. On rocky shores it tends to feed on nudibranchs such as Hermissenda crassicornis, Polycera atra and Dirona picta, while on sheltered muddy or sandy bottoms it feeds on bubble shells such as Haminoea virescens and Bulla gouldiana.

Anatomically Navanax shows no difference from the related genus Aglaja and I suggested many years ago that they should be synonymised. However the name Navanax persists in the popular literature. Species of aglajids like all opisthobranchs are hermaphrodite. In this family the penis is on the right side of the head while the genital opening is on the right side at the rear of the body. To mate, the partner acting as the male has to approach the "female" from behind. Often chains of three or more mating animals will form with those in the middle acting as male and female simultaneously. SEE Reggie Northern Californian Underwater Photographic Society website

Dr Rhanor Gillette's lab has a movie showing Navanax inermis feeding on an aeolid. This shows that like the aglajid genera Melanochlamys and Chelidonura, it feeds by using the buccal bulb as a suction pump. See also Bill Wright's message #16251 reporting Navanax eating Aplysia californica.

• Cimino, G., Crispino, A., Sodano, G. & Spinella, A (1987) Alchilpiridine ed alchilbenzeni da Opistobranchi Bullomorfi: composti relazionati ai feromoni di allarme del Navanax inermis. Atti del XVII Convegno Nazionale della Divisione de Chimica Organica, Societa Chimica Italiana.
• Fenical, W., Sleeper, H.L., Paul, V.J., Stallard, M.O. & Sun, H.H. (1979) Defensive chemistry of Navanax and related opisthobranch molluscs. Pure and Applied Chemistry, 51: 1865-1874.
• Leonard, J.L. & Lukowiak, K .(1984) An ethogram of the sea slug, Navanax inermis (Gastropoda, Opisthobranchia). Z Tierpsychol, 65: 327-345.
• Leonard, J.L. & Lukowiak, K. (1985) Courtship, copulation, and sperm trading in the sea slug, Navanax inermis (Opisthobranchia: Cephalaspidea). Can. J. Zool., 63: 2719-2729.
•Paine, R.T. (1963) Food Recognition and Predation on Opisthobranchs by Navanax inermis. The Veliger, 6(1): 1-9.
•Paine, R.T. (1965) Natural History, Limiting Factors and Energetics of the opisthobranch Navanax inermis. Ecology, 46(5): 603-619.
• Rudman, W.B. (1974) A comparison of Chelidonura, Navanax and Aglaja with other genera of the Aglajidae (Opisthobranchia, Gastropoda). Zoological Journal of the Linnean Society, 54(3): 185-212.
• Sleeper, H.L., Paul, V.J. & Fenical, W. (1980) Alarm pheromones from the marine opisthobranch Navanax inermis. J. Chem. Ecol., 6(1): 57-70.
• Sleeper, H.L. & Fenical, W. (1977) Navenones A-C: Trail breaking alarm pheromones from the marine opisthobranch Navanax inermis. Journal of the American Chemical Society, 99: 2367-2368.
• Spinella, A., Alvarez, L.A., Crispino, A., Marin, A., Villani, G. & Cimino, G. (1992) Chemical signals in some Cephalaspidean molluscs. Abstracts, 11th International Malacological Congress, Siena 1992: 289-290.

Authorship details
Rudman, W.B., 2003 (April 29) Navanax inermis (Cooper, 1863). [In] Sea Slug Forum. Australian Museum, Sydney. Available from

Related messages

  1. Re: Parasites and Navanax inermis
    From: Ernie Hartt, September 25, 2007
  2. Re: Parasites and Navanax inermis
    From: Kevin Lee, August 17, 2007
  3. More on Navanax inermis
    From: Kevin Lee, August 16, 2007
  4. Parasites and Navanax inermis
    From: Kevin Lee, August 16, 2007
  5. Re: Navanax inermis mucus cocoon
    From: Ernest Hartt, August 15, 2007
  6. Might this be Navanax inermis?
    From: Ken Tucker, August 14, 2007
  7. Swimming Navanax from central California
    From: Ron Eby, August 6, 2007
  8. Navanax inermis laying eggs
    From: Bruce Wight, July 28, 2007
  9. Navanax inermis mucus cocoon
    From: Phil Garner, May 23, 2007
  10. Trail following in Navanax inermis
    From: Ernest Hartt, August 29, 2006
  11. Navanax - Aplysia interactions
    From: William G. Wright, April 7, 2006
  12. Navanax eating Aplysia
    From: Brad Bartczak, September 17, 2005
  13. Is this Navanax?
    From: Peter McGuinness, December 28, 2004
  14. Re: Strange lunch for Navanax
    From: Ernie Hartt, December 18, 2003
  15. Strange lunch for Navanax
    From: Bruce Wight, November 15, 2003
  16. Navanax - yellow secretions
    From: Tammy, October 13, 2003
  17. Navanax inermis from Long Beach, California
    From: Crystal, April 30, 2003
  18. Re: Navanax larval culture
    From: Bill Rudman, March 21, 2002
  19. Larval development of Navanax
    From: I.M. Loeza & A.M. Ortiz, March 19, 2002
  20. More photos of Navanax inermis
    From: Daniel Geiger, July 29, 2001
  21. Some photos of Navanax inermis
    From: Daniel Geiger, July 27, 2001
  22. Predators of Navanax inermis
    From: Shannon, March 10, 2001
  23. Cannibalism in Navanax inermis
    From: Ernie Hartt, February 19, 2001
  24. Navanax diet
    From: Vincent A. Parsick III, January 27, 2001
  25. Navanax inermis
    From: Erwin Koehler, October 3, 1998

Show factsheet and all related messages