Dive Dry with Dr. Bill

#327: A Skeleton of a "Shrimp"

The past two weeks I've done a lot of "trash talk." Time to get back to the critters. I've finally kicked the 8-9 week bout with a cold and my lungs were ready for a dive. Fortunately I had to wait another week to submerge because my son Kevin and his long-time girlfriend Mary got married in San Clemente last weekend. Even though I was scheduled to arrive in the Galapagos on their special day, my son comes first. I stood there on the beach, filming them and their guests with my high definition video camera. The smiles on their faces said it all... they really were ecstatic and it moved me. In fact, I decided that maybe I should try marriage myself... in some future reincarnation, of course! I wanted to share that wonderful news with my readers. However, it has nothing to do with the subject of this week's column, so read on.

The weekend before the wedding I was down at the dive park talking with friends. Lifeguard and ScubaLuv instructor Paul had been cleaning boat hulls much of the day and asked what all the creepy, crawly things were still clinging to his wetsuit. I took a look and saw dozens, if not hundreds of critters moving about his wetsuit like inchworms on a tomato plant. I was able to quickly identify them as caprellid amphipods, commonly known as "skeleton shrimp." Looking at their very slender, almost tubular bodies one can see how they were given this name.

Caprellids are members of the phylum Arthropoda and class Crustacea to which real shrimp, crabs, lobster and other hard-shelled tasties belong. Unlike their relatives, they are much too small and skinny to provide a satisfying meal for this hungry man! However, they are really cool critters in my book, and I took several back to my lab (er, house) to observe and photograph under the microscope.

Amphipods as a group are squashed (a technical term) from side-to-side, unlike their relatives the isopods which are flattened top-to-bottom. The forward end of a caprellid includes the head with its antennae and unstalked eyes. The middle section, or thorax, contains some claw-like structures known as gnathopods which look somewhat like a praying mantis' predatory paws. To paraphrase Cassius Clay (er, Muhammad Ali to you youngsters), caprellids float like an inchworm and sting like a mantis. The flat, leaf-like gills and brood pouches for their young are also found on this portion of their slender bodies. At the small "tail" end or abdomen, there is no tail... just a set of legs with grasping, claw-like structures that anchor them to seaweed, reefs and Paul's wetsuit.

Caprellid amphipods are multi-modal munchers... that is they can feed in several ways. We have a lot on common. I also visited my friend Sheena Liu last week and she fed me all sorts of exotic fruits and vegetables, expanding my diet from the normal pan dulce, burritos and steaks. Some caprellids use the long antennae on their head to filter plankton from the water and pass it to their mouths. Although most amphipods are not predators, the caprellids can be very active feeders on other small critters using their gnathopods. Victims include the polyps of hydroids, generally tiny relatives of jellyfish and sea anemones; and equally small bryozoa. Some skeleton shrimp will anchor themselves with their rear leg claws, "stand" up motionless and outstretched, and use their gnathopods to grab small critters that drift past.

Skeleton shrimp can also feed in a manner similar to that of their "beach hopper" amphipod relatives. They can capture organic debris from the water column. Caprellids also scrape tiny diatoms, dinoflagellates and other organisms off the substrate. They will scavenger on dead crustaceans. It seems like the only feeding mechanism they can't employ is to create their own food by photosynthesis like algae and land plants.

Any description of a critter should detail not only their munching behavior, but their mating rituals as well.... after all, "munching" and "mating" in the Macrocystis (giant kelp) is the focus of my educational DVDs and cable TV shows! It appears there are few voyeuristic scientists who spend their hours observing and documenting such behavior. I found nothing in the literature about their amorous interactions. However, once the "dirty deed" is done, the females carry their young in brood pouches on the underside of the thorax. You'll have to be satisfied with that tidbit of knowledge.

Earlier I mentioned that skeleton shrimp move like inchworms in your garden. They use the rear and forward legs to accomplish this. However, caprellids are also capable of swimming through the water column. They do so using rapid flexing and extending of their long, slender bodies. When doing so, I assume they look somewhat like this flailing diver as they move through the water column. At least I don't have to fear getting munched by a fish... except, perhaps, the "landlord." Gulp!

© 2009 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 and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. Please help me climb out of self-imposed poverty... buy my DVD's (see this link). Yes, take Dr. Bill home with you... we'll both be glad you did!

A caprellid amphipod under the microscope, the nasty gnathopods used to crush prey;
the antennae used to filter food and the leaf-like gills on the thorax.

This document maintained by Dr. Bill Bushing.
Material and images © 2008 Star Thrower Educational Multimedia