Most annelids are small creatures that live under the soil or sea bed. They feed by tunneling through the sediment and ingesting everything they come across, digesting the organic material and passing the inorganic. However, in a phylum that comprises over 15,000 known species there are bound to be a few exceptions. The giant earthworm of New Zealand, while harmless, can reach a length of over six feet. Then there’s my friend Eunice.
Above is the portion of an aquarium bottom where Eunice lives. Eunice is a giant bristle worm (Eunice sp.). She never comes out during the day but stays in her nest that she secreted with slime produced by glands in the mouth. It looks and feels remarkably like a spider web, and like a spider the worm produces a liquid substance that solidifies as it leaves the body. The nest material is sticky and clings to the glass sides and tank bottom. Over time it collects bits of rocks and gravel which strengthens the nest into a fortress. I’m assuming she purposely adds the rocks at night since I’ve never actually seen her doing this, but each morning there is another layer of gravel stuck to the webbing.
In order to photograph her I had to poke my finger into one end of the nest to get her to escape out the other side. These worms are armed with a set of jaws that work like a steel trap, and the fangs are tipped with a mild toxin, so the bite she can give can be pretty nasty. Since you can’t see through the nest I had to just keep my fingers crossed that I was choosing the right end of the nest to prod.
Once she leaves the nest I can move her to the photographing tray. As you can see, she’s a monster. At over three feet in length it is the longest annelid I’ve ever seen. Because of those fangs I had to be careful to keep my hands away from the head. What I didn’t count on was how fast she can move.
I got Eunice from a friend who cultivates corals and sells them to the aquarium trade. Propagating corals is sort of like propagating plants in a greenhouse. He has a "mother" specimen of each type and as the coral grows he snips bits of "daughter" corals off and grows them on little ceramic tiles. Although the water system needed to grow corals is very elaborate (and equally expensive), it’s actually a very eco-friendly way of supplying these animals to hobbyists. Properly done an infinite number of coral heads can be developed from a single piece, eliminating the need to harvest wild stocks.
In fact, this guy has become so adept at this process that he now has clients all over the world who send him their sick and dying corals so he can rejuvenate them. This is how Eunice came along. A large hotel in the Bahamas mailed him a rare coral head they had in their lobby that was dying. The first step is to chisel away the dead parts so he’s starting with a relatively healthy colony.
He removed the coral from the shipping crate and started to split off the dead parts. When his first strike cleaved the colony in two Eunice came shooting out of the wreckage, landed in the water and burrowed under another coral head. All before he could even react. He called me to come and get this thing out of his house and I was glad to oblige. You may have noticed in the second paragraph I identified this worm as "Eunice sp". This means I know which genus she belongs to but I’m unsure of the species. One problem is that I really don’t know where she originally came from, although based on her size and the type of coral she was found in I’m guessing Northern Australia.
Annelids are segmented worms and come in two types: Oligochaetes, which have bristles, or setae on each body segment, and Polychaetes which have setae as well as parapodia. Parapodia, meaning "almost feet", are appendages that help the animal to dig and move. An example of an oligochaete is the common earthworm, while Eunice here is an example of a polychaete.
Eunice’s parapodia are worth taking a closer look at, and you’ll be able to see them in action in the video at the end of this essay. Parapodia are paired and occur on each of the hundreds of segments that make up this worm. Growing off the parapodia are the setae, or bristles. In the photo below, the long extensions are usually mistaken for the parapodia. These are actually the bristles, the parapodia being the darker and shorter structures at the base.
The common name for this group of animals is "bristle worm", obviously named after the prominent setae this group sports. What I didn’t know until later was that you should never handle a large bristle worm without gloves. When threatened the worm can erect the bristles so that they shoot out the sides, and even detach. The strength of the setae is enough to puncture the skin. And to make matters worse, each bristle is tipped with a silica barb, which while not toxic, acts like an irritant and can produce painful sores and lacerations that can lead to infection. So, what I’m doing in that photo up top? Don’t do it.
I tried to get Eunice to eat something during this photo shoot, but being strictly nocturnal, she had no interest. The feeding behavior is pretty impressive. Bristle worms are mainly scavengers, but will also hunt at night. When feeding the jaws, which are hidden in an internal sac-like structure called a pharynx, emerge from the mouth and add another inch to the worms overall length. As the jaw clamps shut on the prey the internal mouth sac inverts and covers the jaws and the prey in the hood. The mouthparts are then retracted, pulling the food into the worm’s body. The soft structures around the mouth in the photo below are sensory organs used to locate the prey.
Now here’s a video of Eunice, and I want to point out two things. First, during the closeups watch for the movement of the parapodia. Second, this worms exhibits iridescence, which is an optical illusion of color changes as light hits the skin cells from different angles.
I tried to show the iridescence a little better, but with my little Nikon I didn’t have much luck. This footage from National Geographic shows worm iridescence a little better, although it’s not the point of the video.
So, the photo shoot’s over and Eunice is beat (you can tell because she let the back half of her body remain twisted over in the video), so I placed her back into her home tank again. She immediately went right back into her cocoon. The next morning what little damage I had done to the nest while prodding her out had been repaired overnight.
Other diaries in this series can be found here.
