Feather Duster Worm (Eudistylia vancouveri)
This conspicuous and beautiful species is a prominent part of the diverse fauna encrusting the sea bottom in the Pacific Northwest. They may also be seen growing on pilings and floats, where their activities can be watched without the need of a wet suit and scuba tanks. The visible part of the worm consists of a ring of feathery, brightly colored, tentacles that wave gently in the current. Below that is a calcareous tube that may be as much as 45 cm long.
When a potential predator such as a fish or diver comes near, the tentacles disappear in a flash, pulled inside a calcareous tube, which then closes over them. Although the worm has no obvious eyes, the reaction is clearly a light-sensitive one. Giant nerve cells allow such a quick reaction. The tentacles are at the anterior end of a worm that grows to 25 cm in length, and they serve as feeding appendages, filtering out plankton that drift by. Plankton-feeders such as this often live where there are strong currents and wave action, moving food past the animal at a high rate.
Each “tentacle” is a radiole, a much-branched structure that carries food particles toward the mouth. The significance of their bright coloration is obscure, but they certainly add color to the sea bottom where they occur. These structures are amazingly complex, able to direct particles in the water to a central food groove, which then sorts them by size so that the smallest go to the stomach, the largest are discarded, and the mid-sized ones go into making the tube.
Fecal pellets, excreted at the rear end of the worm, move forward along a groove on the ventral side of the abdomen, which then twists around and runs on the dorsal side, where the pellets are extruded from the mouth and washed away.
The sexes are separate in these worms, but gametes are produced on internal surfaces rather than in gonads. During spawning, the sperm and eggs are carried up the same groove that carries the fecal pellets and shed into the water. Fertilization is thus a random process, and the larvae that develop are planktonic spheroids with flagella and cilia, at first looking nothing like worms. They add segments little by little and finally drop out of the plankton as real worms, to begin their feather-duster life.