Dive Dry with Dr. Bill

#195: Hey Sluggo... Dr. Bill Here!

I've mentioned that San Diego was a very productive dive site for my dive buddy Andrea and me. Another of the unusual critter encounters we had there was with the California sea slug. This species of snail is the only member of its scientific family that I've seen in our waters. Must have be a very dysfunctional family!

This relative of the nudibranchs and sea hares is somewhat non-descript in appearance, unlike many of its very colorful relatives. Its body is a mottled brown and is covered with numerous bumps on top. The foot and broad "veil" around the mouth are lighter in color. and the veil has several fleshy protuberances. This sea slug has a relatively large head for its body size. The individual we found was only about four inches long, but my research indicates they can grow to over a foot in length!

In spite of its large size, the California sea slug is said to be nearly neutrally buoyant... must have had a very good SCUBA instructor. It is capable of crawling at speeds up to a yard a minute, pretty fast for a "snail's pace." When disturbed (physically, not psychologically), it can "swim" by awkwardly twisting its body back and forth. While I haven't seen this behavior, it sounds like it needed a better swimming teacher! If push comes to shove, it employs other defenses. It can deliver an irritating bite, and it secretes strong acids from its body surface.

This species is a deep water form found on fine sand and mud down to 1,200 feet. I may do an occasional deep dive, but certainly not that deep! I'll leave those excursions to fellow Cousteau associate "Her Deepness," Dr. Sylvia Earle, who once served as a board member of the Catalina Island School and holds the record for the deepest untethered solo dive at 1,250 feet in 1979. The species is known from Oregon to... San Diego, so I found it at its southernmost range. Although it was observed on Santa Cruz Island to the north, I'm not aware of any records from Catalina.

The California sea slug may be a snail, but plants are not its preferred food! It is a voracious predator and scavenger, feeding on a number of different invertebrates and even an occasional fish. It will feed on almost any "cut" of meat, including sea anemones, dead squid, other snails and even members of its own species (I told you they must be dysfunctional!). When feeding, it everts a huge (and very interesting, at least to Andrea) proboscis which has strong jaws and a large scraping radula. Even relatively large menu items can be swallowed whole.

This snail appears to prefer "munching" over "mating." Even when two are placed together in an aquarium, they may not mate... perhaps they just prefer a little privacy, scientists! If they do mate, they will often separate and feed when a meal presents itself. I think it is pretty clear where their priorities rest. The only time they seem to control their hunger is while laying their eggs. This is probably a biochemical evolutionary mechanism triggered by hormones to prevent them from eating their own eggs as a tasty form of caviar. Their large nerve cells are often used by scientists to investigate the physiological nature of behavior and learning. The "nerve" of some researchers. Of course such study is well merited since these slugs obviously have their "munching" and "mating" priorities all mixed up!

© 2006 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM weekdays. Please help me climb out of self-imposed poverty... buy my "Munching and Mating in the Macrocystis," "Great White Sharks of Guadalupe," "Calimari Concupiscence: Mating Squid, " "Playful Pinnipeds: California Sea Lions," "Belize It or Not: Western Caribbean Invertebrates, Fish and Turtles" or "Gentle Giants: Giant Sea Bass" DVD's. Yes, take Dr. Bill home with you... we'll both be glad you did!

A California sea slug cruising for cuisine on the ocean floor. Notice the
unusual proboscis-like mouth in the lower left.

This document maintained by Dr. Bill Bushing.
Material and images © 2006 Star Thrower Educational Multimedia