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Polychaetes ('many hairs') belong to a phylum of cylindrical soft-bodied invertebrates, Annelida, which date from the Paleozoic era. An annelid's body structure consists of a fluid-filled 'tube-within-a-tube', or coelum, with a projection that resembles a head at one end. They are bilaterally symmetrical and have a closed circulatory system. Their bodies produce red blood, and many species have hemoglobin. Each of the bristle worm's body segments has a pair of small parapodia, or paddle-shaped appendages, in which are embedded tiny hairs or bristle-like structures. Most species also have well-developed sense organs, a 'head' that includes eyes, antennae and sensory palps. Background
Nearly 10,000 species of bristle worms have been noted. Some bristle worms can be found living on the bottom in the ocean's deepest waters, or floating near the surface. Some species can reach a length of three meters. Also known as lugworms, clamworms, fire worms, sea mice and feather duster worms, many bristle worm species are carnivorous, and crawl actively in search of prey. These are mobile predators, capturing their food and then burrowing in sand or mud. Other species of bristle worms are sedentary and build tubes from sand or mucus, from which they rarely stray. . The several species common to the Bay generally fall into two categories: either they burrow in mud and sand in coastal areas, or they construct tubes and wait for food to come to them. Both types of worm are abundant in the Bay and its rivers, and they play important ecological roles, by consuming small invertebrates and by serving as food for larger invertebrates and fish. Clamworm
Nereis succinea, the common clamworm, is a wandering benthic predator, and one of the most widespread bristle worm species in the Bay. This clamworm can reach a length of five or six inches but it's more common to find smaller specimens. Its anterior portion is usually brown, the body a reddish-brown. The 'head' has four eyes, two palps (sensory feelers protruding from the clam's mouth) and eight tentacles. When feeding, the clamworm's proboscis emerges, with two hooks at the end. It grasps its prey, and then retracts the proboscis to draw the food-usually other worms, parts of fish, or algae-into its mouth. Clamworms are mobile, voracious creatures, but they also are the favorite prey of bottom-feeding fishes and crustaceans. For protection the clamworm secretes a mucus-based substance that hardens around them like a sheath, and from which they can come and go rapidly. During dark lunar phases in spring and early summer, clamworms become 'heteronereises'-a sexual form that results in two important changes: their parapodia become enlarged, allowing them to swim, and they become capable of releasing either eggs or sperm. If you shine a flashlight into the water on such a dark night, you may see hundreds of clamworms at the surface of the water in circles. After several nights of this activity, clamworms release eggs and sperm, and then die. Planktonic larvae develop, called trochophores, which become juvenile annelids, eventually settling at the bottom as mature clamworms. Glassy TubewormBristle worms belonging to the second group, the tube-builders, are passive consumers that have evolved more specialized palps for obtaining food. Their palps tend to be longer and resemble tentacles, and their "feet" are not as developed. Spiochaetopterus oculatus, the glassy tubeworm, creates transparent vertical tubes with rings that resemble bamboo. Both tube and worm are smaller than other species-usually about two inches long, but a fraction of an inch in diameter. The glassy tubeworm uses its two long curling palps to grasp its prey. Red-gilled Mud WormThe red-gilled mud worm, Marenzellaria viridis, is one of the Bay's largest mud-worm species, reaching a length of four inches or more. This species occurs frequently in sandy, intertidal areas, burrowing vertically and creating a mucus-based, mud-covered tube. To feed, this mud worm extends its head from the tube and grasps prey with its palps. Its crimson gills and prominent bristles make it easy to identify. Unlike the clamworm, the red-gilled mud worm spawns usually at night on an ebbing tide in late winter.
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