Defenses of nudibranchs and their relatives include alarm pheromones, considered in this section, and
CAMOUFLAGE (CRYPSIS),
FAST CRAWLING & SWIMMING,
MUCOUS COATINGS,
CERATAL AUTOTOMY,
NUTRITIONAL CONTENT,
SPICULES,
NEMATOCYSTS,
VACUOLATED SKIN WITH PROTECTIVE SPINDLES,
ACID SECRETIONS,
INK & OPALINE SECRETIONS,
SECONDARY METABOLITES,
APOSEMATIC (WARNING) COLORATION & BATESIAN MIMICRY, and
NAVANAX: A SPECIAL CASE STUDY, considered in other sections. 

The cephalaspidean Navanax inermis occurs from northern California to the southern limits of the Gulf of California.  It is a predator of other opisthobranchs, most notably other shelled species, but may even prey upon conspecifics.  On attack, Navanax releases a yellow hydrophobic substance from a “yellow gland” near its anus directly onto its slime trail.  The secretion does not dilute in seawater but adheres to the slime trail, which can persist for several days.  Other Navanax, perhaps searching for a meal along the slime trail, turn away. The response is well defined, consisting of contraction, turning at an angle greater than 90^o, and retreat. Studies at Scripps Institution of Oceanography, La Jolla, California show that the substance is a mix of 3 related conjugated methyl ketones called navenones, synthesised de novo by Navanax.  After its release, the depleted navenone supply is topped up within 3-7d.  The authors describe the secretion as an alarm pheromone, presumably because it communicates a message to conspecifics warning them of danger.  However, if its function is to ward off potential predatory species including conspecifics looking for a meal, then its role may be dual: both a defensive chemical and an alarm pheromone.  Sleeper & Fenical 1977 J Amer Chem Soc 99: 7; Sleeper et al. 1980 J Chem Ecol 6: 57.  Photo courtesy Kevin Lee, Fullerton, California diverKevin.

Navanax inermis 1X