Polychaeta

Polychaeta is a class of annelid worms, generally marine. Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are made of chitin. More than 10,000 species are described in this class. Common representatives include the lugworm and the ragworm.

Characteristics

Polychaetes are extremely variable in both form and lifestyle, and include a few groups of species that swim among the plankton or above the abyssal plain. However, most species live in tubes or burrows, and a minority are active swimmers.

Anatomy

The head, or prostomium, is relatively well developed, compared with other annelids. It projects forward over the mouth, which therefore lies on the animal's underside. The head normally includes two to four pair of eyes, although some species are blind. These are typically fairly simple structures, capable of distinguishing only light and dark, although some species have large eyes with lenses that may be capable of more sophisticated vision.

Reproduction

Polychaetes have a variety of reproductive strategies. Most common is sexual reproduction, with separate male and female individuals, but some species are hermaphroditic. In some species, individuals are either male or female throughout their lives, but in others they may change sex as they age.

Ecology

Polychaetes play important roles in marine ecosystems, both as prey items for a wide variety of organisms and as predators on other marine organisms.

See also

• Annelid
• Lugworm
• Ragworm

External links

• World Register of Marine Species: Polychaeta

Polychaeta Resources
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