Dive Dry with Dr. Bill

#243: The Horned Aeolid

As Port Captain Renzo Sampson reminds me come July or August each year, summer is the time for scantily clad semi-aquatic bipeds who often inhabit the beaches at Descanso, Avalon and Lover's Cove. Spending as much time as I do underwater during the warm season, I rarely get a chance to adequately study this particular species (or at least the half of them that appeal to me) closely using my binoculars. Instead, I find myself dealing with another group of scantily clad critters... the ones whose name translates to "naked gills." Yes, it's time again for nudibranchs (or "nudies" as many divers call them).

My new HDV (High Definition Video) camera has given me the opportunity to record some high quality video footage of these often beautiful snails, as well as capture higher resolution stills for my newspaper columns. Make sure you "tune in" to my "Dive Dry with Dr. Bill" cable TV show to see the results with your own eyes. However, if you are a child of the 60's, I don't expect you to "turn on" or "drop out..." we're much too old (er, mature) for that. Unfortunately my last remaining underwater video light flooded last weekend, so until I can rob our local bank a few times and buy new video lights, I won't be getting any more of this spectacular footage. It would take two years of writing this column to earn enough to pay for them.

One nudibranch I've never captured adequately with my older, lower resolution camcorders is Hermissenda crassicornis. For the past 40 years I'm not sure I ever knew it had a common name, the horned aeolid. But then I'm at the age where memory is the second thing to go. This species has been pretty common the past few months, especially at cooler offshore dive sites like Ship Rock and Eagle Reef. In fact, I've spent more than one dive at these sites almost entirely on this beautiful species of shell-less snail. They are found from Japan and Alaska south to Bahia de Los Angeles, Mexico.

The horned aeolid is a member of the aeolid nudibranchs. This group has what appears to be a shag carpet on its dorsal surface. These are actually the "naked gills," referred to as cerata. Hermissenda's are a beautiful reddish-orange tipped with cream or white, although there are a few less common color variants. The gills are responsible for gas transfer between the animal and its ocean environment. They take in oxygen from the water and release carbon dioxide.

There are two sets of "appendages" in the head region. The oral tentacles extend outward from the head and mouth, and are used for sensing the environment. Extending upward from the head are the two rhinophores which have a horn-like appearance, hence the common name "horned aeolid." There is a nearly flourescent orange stripe running from the head back along the top of its dorsal surface. This is contrasted by a beautiful blue line along the oral tentacles in front, reaching back along the lower outer surface of the foot. These colors are best captured with high resolution video or still cameras, not my failing eyes.

Nudibranchs are often "vicious" predators... vicious if you are a tiny hydroid or bryozoan, or even one of their own relatives. These carnivores generally like cooler waters which are richer in nutrients. This ensures that their filter feeding food favorites will be abundant. Now hydroids are tiny organisms related to coral, sea anemones and jellyfish. Like most members of their phylum (Cnidaria), they have stinging cells to capture food, and for defense. The nudibranchs that feed on them have evolved an interesting and fairly effective defense mechanism. When they eat the hydroids, the stinging cells (known as nematocysts), are incorporated into the "naked gills" and can be used to sting a predator which tries to eat the nudibranch. So the cerata might also be called "naked guns." I wish our Pentagon and the military-industrial complex former President Ike Eisenhower warned us about were as creative... and budget conscious!

It is said nudibranchs have another defense mechanism... they reportedly don't taste very good. My marine biologist icon, Edward F. "Doc" Ricketts of Steinbeck's Cannery Row fame, is said to have tried tasting one once and declared it to be true! Now I'm not sure fish have as sensitive a palate as Doc's. I know mine is non-existent based on what I microwave for dinner. I have a sneaking suspicion that sheephead, kelp bass, garibaldi and other fish will take nudibranchs in a pinch. After all, I've seen them eat live jellyfish tentacles, which have more potent stinging cells, so they do enjoy spicey food. I think this may be why most of the nudibranchs I see off Catalina are at depths below 100 feet where these fish are less common. On the largely overfished mainland coast, you can find more nudibranchs in shallow water.

Now I would be remiss if I didn't mention another important aspect of these nudibranchs. Like most of their relatives, they are simultaneous hermaphrodites. Remember way back when I defined that term for you? I didn't think so. It means they have both functioning male and female sex organs. Nudibranchs are a truly good example of "Munching and Mating in the Macrocystis (giant kelp)" since they are often seen doing one or the other. When they mate, they follow the William Wrigley Jr. Company's advice to "double your pleasure, double your fun." Yep, they line up head-to-tail with both male parts next to both female ones. I'll leave the rest to your fertile imagination. So I guess you could call the "horned aeolid" the "horny aeolid" as well.

© 2007 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," "Gentle Giants: Giant Sea Bass" or "Common Fish and Invertebrates of the Sea of Cortez" DVD's. Yes, take Dr. Bill home with you... we'll both be glad you did!

The beautiful horned aeolid or Hermissenda crassicornis with its egg mass (but no X-rated mating pictures).

This document maintained by Dr. Bill Bushing.
Material and images © 2007 Star Thrower Educational Multimedia