Nereididae - Bristle Worms (Polychaetes)

Polychaetes belong the phylum Annelida, the segmented worms. The phylum also includes the classes Hirudinea, which contain the leeches, and the Oligochaeta, the earthworms. The class Polychaeta are the marine worms, such as the nereids (sandworms) and glycerids (bloodworms). Polychaetes differ from the other classes by possessing parapodia (leg-like appendages), setae (small hairs) projecting from the parapodia, and anterior appendages (antennae, palps, tentacles) which are usually lacking in the other two classes. Earthworms and leeches are also hermaphroditic (both sexes in a single individual) whereas the polychaetes are dioecious (sexes on different individuals).

Polychaetes are mostly marine with very few freshwater or terrestrial species occurring. Their habitats range from the intertidal zone to the deepest depths of the ocean, including the hydrothermal vents of the Pacific Ocean. Their class is divided into two groups, the errant polychaetes and the sedentary polychaetes. The errants are usually free swimming or crawling but sometimes will burrow in crevices or under rocks. Their parapodia and setae are well developed. Some (e.g. the fireworm) have a toxin in their setae that will produce a nasty stinging reaction in humans. The sedentaries usually live permanently in tubes or burrows or sometimes attach to rocks or pilings. This group includes the beautiful feather duster worms found in reef areas. Their appendages (parapodia) are reduced and their setae are sometimes hook-shaped to help the worm hold itself to the wall of its tube.

Nereididae worms, commonly called ragworms or clam worms, are errant polychaetes. They are characterized as having distinct heads with two pair of eyes, two palps, one pair of antennae and four pair of longer tentacles. The most common nereidid in Texas is probably the common clam worm, Alitta succinea. In the spring and summer it swarms at the surface en masse, especially at night around lights, to spawn. This increases the chance that the eggs and sperm released into the water come in contact with each other.