Bristle WormsPolychaete

By: Jayme De La Vega

TaxonomyKingdom- Animalia

Phylum- Annelida

Class- Polychaeta

About Polychaeta or polychaetes are a polyphyletic class of annelid worms, generally marine.

Each body segment has a pair of fleshy protrusions (lumps) called parapodia that bear many bristles, called chaetae, which are made of chitin.

Annelid worm

Where are they? Polychaetes as a class are widespread

with species that live in the coldest ocean temperatures of the abyssal plain to forms that tolerate extreme high temperatures near hydrothermal vents

Description Polychaetes are segmented worms, Generally less than 10 centimeters (3.9 in) in length,

although ranging at the extremes from 1 millimeter (0.039 in) to 3 meters (9.8 ft).

They can be either brightly colored, iridescent or luminescent

Each segment bears a pair of paddle-like and highly vascularized parapodia, which are used for movement and, in many species, act as the worm's primary respiratory surfaces.

Bundles of bristles, called setae, project from the parapodia. The mobile forms (Errantia) tend to have well-developed

sense of organs and jaws Stationary forms (Sedentaria) lack them but may have

specialized gills or tentacles used for respiration and deposit or filter feeding

Continued Underwater Polychaetes have eversible

mouthparts used to capture prey. A few groups have evolved to live in terrestrial environments,

Body Forms Most polychaetes crawl along the

bottom floor, but others have adapted to burrowing, swimming, tube-dwelling and commensalism (two organisms, one benefits the other is not harmed)

Reproduction Most polychaetes have separate sexes, rather than being

hermaphroditic. The most primitive species have a pair of gonads in every

segment, but, in most species, there has been some degree of specialisation.

The gonads shed immature gametes directly into the body cavity, where they complete their development.

Once mature, the gametes are shed into the surrounding water through ducts or openings that vary between species, or in some cases by the complete rupture of the body wall (and subsequent death of the adult).

A few species copulate but most fertilize the eggs externally.

Continued The fertilized eggs typically hatch into

trochophore larvae, which float among the plankton, and eventually metamorphose into the adult form by adding segments

Bibliography http://en.wikipedia.org/wiki/Polychaete