The bristle worm is an annelid, or segmented worm, and has a fluid-filled and symmetrical body. It belongs to the class known as polychaetes (many hairs), and has several pairs of paddle-shaped appendages (parapodia), which contain tiny bristle-like structures. In one species, the fireworm, the bristles are filled with poison, but are also fragile, and when broken pierce the skin. Bristle worms usually have highly developed sensory organs, including eyes, antennae, and sensory palps. Bristle worms are found deep within the sea, floating near its surface, and in intertidal reefs.
There are two kinds of bristle worms: Errantia, which swim, crawl, or burrow for their food; and Sedentaria, which live within a permanent tube in the sand, and wait for food to come to them. The sedentary species burrow through the sand and extend their mouths, which are surrounded by mucus. Particles stick to the mucus, are drawn into the body, and pass through the gut where they are digested. Some of the mobile varieties have scissor-like teeth which they use to cut off bits of algae or dead animals they happen across, while others have jaws they use to kill living prey.
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Most bristle worms reproduce by shedding sperm and eggs into the water, where they are then fertilized. The eggs and sperm are produced in the worm’s back section, and released during a specific combination of the tide, moon phase, and water temperature. After fertilization, the eggs grow into swimming larvae, and once they have about nine segments, they leave that water and start searching for a place to settle.
There are nearly 10,000 known species of bristle worm, including:
The clamworm (nereis succinea) is a mobile species, and uses its proboscis (a needle-like protrusion) to grab and draw prey into its mouth. Clamworms usually feed on other worms, dead fish or algae. The clamworm’s predators include bottom-feeding fishes and crustaceans; to protect itself, the clamworm secretes a mucus-like substance that hardens around its body, but from which it can come and go easily.
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The glassy tubeworm (spiochaetopterus oculatus) is a sedentary tube-builder, with palps that are longer than in other worms, and resemble tentacles. The glassy tubeworm constructs transparent, ringed, vertical tubes in the sand, and uses its palps to grab prey that move toward it. The glassy tubeworm is smaller than other bristleworms, being no more than about two inches long.
The red-gilled mud worm (marenzellaria viridis) is one of the larger species, at about four inches or more in length. They are often found in sandy, intertidal areas, where they construct mucus-based tubes covered in mud. They feed by extending their heads and grabbing prey with their palps.
These are just a few examples of the bristle worm. Bristle worms are a diverse lot, from benign to pain-inflicting, from passive to aggressive, and from ugly to cute, but they are always interesting.