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The Robinson Library >> Phylum Annelida
About the Phylum Annelida

The word "Annelida" comes from the Latin annelus, or ringed.

Characteristics (1) Segmented body; (2) digestive tract with two openings; (3) body cavity.

simplified diagram of an Annelid

Size Less than an inch to over 3 yards, with varied shapes.

Habitat Soil, also all waters and sandy shores.

Other Characteristics Segments are often provided with bristles, or setae. The digestive tract, ventral nerve cord and major blood vessels run uninterrupted the length of the body; all other organs are placed within certain segments.

Class Polychaeta -- (about 4,000 species) -- Common but inconspicuous marine creatures, polychaetes burrow in the sand, crawl under rocks or live within tubes partially buried in sand or mud. Thousands of such tubes may be seen dotting a tidal flat at low tide. Polychaetes often have a well-developed head with eyes and antennae. A pair of lateral appendages on each segment aids in movement.

Class Oligochaeta -- earthworms (about 2,700 species) -- Lacking appendages, these worms move by extending and contracting the body. They live in the bottoms of lakes, ponds and streams or burrow in soil. Certain body segments are sometimes swollen by glands which secrete mucus for the construction of cocoons in which the hermaphrodite worms deposit their eggs. Most species run several inches in length but one Australian type may be as much as 10 feet long.

Class Hirudinea -- leeches (300-plus species) -- These primarily fresh-water annelids have rather flattened bodies with a sucker at each end. Many are scavengers or feed on small invertebrate animals. A large number are bloodsuckers and attack snails, fish, turtles and other aquatic animals.

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The Robinson Library >> Phylum Annelida

This page was last updated on 09/28/2018.