A headshield slug that hunts other sea slugs by following their slime trails and swallows them whole.
Sources give anything from 2.5 to 10 cm. A flattened slug with a head shield, a rounded rear edge to that shield, two lobes behind it, and large side flaps folded over the back. It is usually dark with blue spots along the margins of the flaps, though the spots are variable and sometimes absent, and the colour varies from place to place.
It is a cephalaspidean, not a nudibranch. It hunts other sea slugs: it follows their mucus trails and swallows them whole, and it eats its own kind as well. The lettuce sea slug is recorded prey. Look for it on sand, rubble and seagrass, often working along a visible slime trail. It lives from tide pools down to about 30 m.
The name is a problem worth stating. The slug of the Gulf of California, which is the animal usually called the Sea of Cortez navanax, is a different species. This one was described from Pacific Panama and its usual names are the riddle navanax or the Panama aglaja. It is also unsettled taxonomically: the name has been split and re-lumped, most recently in 2012, and species boundaries within the group are still debated.
The Galapagos record is confirmed. The Revillagigedo record could not be confirmed in any published source and needs checking.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.
