Navanax inermis--a rat-size, yellow-dotted brown-and-blue sea slug--is a bit odd even by the laid-back standards of its native California. It crawls around mud flats on a single foot, from which extends a round flap of sensitive skin. Much of the time the slug wraps this cloak of flesh around its tubular body, making it look like an undulating, psychedelic enchilada.
Its weak eyes supplemented by a phenomenal sense of smell, Navanax creeps about the shallows of salty inlets, grasping and gulping down other creatures with the suction it creates when it rapidly stretches its innards. When two Navanax meet, one usually tries this on the other. Only if the other is too big to snack on, or if one approaches the other from behind, do they turn to the next best thing, which is having sex.
It’s sort of a legend up and down the West Coast, says zoologist Janet Leonard of Oregon State University’s Marine Science Center. Navanax, the ‘if you can’t eat it, mate with it’ animal. Befitting stereotypes about life in southern California, she says, Navanax doesn’t seem to have much else on what could loosely be termed its mind.
In fact, Navanax and its fellow sea slugs have become a favorite of neurobiological researchers precisely because a slug’s brain and behavior are a lot easier to map than, say, a cat’s or a mouse’s. Yet when one Navanax creeps up behind another and initiates sex, both slugs soon face a decision that’s almost never addressed by grander, fancier brains: when to be male and when to be female.
