Oligochaetes include the earthworms and a few small freshwater, estuarine, and recently described deep-sea forms. There are also some soil and freshwater (in the Great Lakes and Lake Baikal) polychaete species. The concretelike tubes of some polychaetes foul ships. Marine polychaetes include Aphrodite, the hairy sea mice lugworms ( Arenicola), which burrow in sand and mudflats sabellid and serpulid worms, whose tubes encrust shells, rocks, and algae, including peacock worms ( Sabella), which construct mosaic tubes of sand or shell economically important bait worms such as Nereis and a few pelagic ( ocean dwelling) species. Free-living polychaete species are grouped as errant polychaetes. Some tube-dwelling polychaetes leave their tubes, others do not all of these tube builders are grouped as sedentary polychaetes. In a few polychaete species, chitinous rods called acicula support parapodia. Parapodia of all polychaetes with few exceptions are stiffened by a bundle of chitinous bristles, enabling the parapodia to function as oars and levers. In most polychaetes (paddle-footed worms), a fleshy lobe ( prostomium) projects over the ventral mouth and bears tentacles. There are about 9000 species of polychaetes, including myzostomarians, a group of about 100 species of small polychaetes that live on or in echinoderms (Phylum Echinodermata), 6,000 species of oligochaetes, and 500 species of hirudinids. Some carnivorous polychaetes have fangs with which they inject toxins into prey.Ībout 15,000 species of annelids are grouped into three classes: the Polychaeta, mostly marine and a few soil and freshwater bristle worms the Oligochaeta, terrestrial and freshwater bristle worms and the Hirudinea, or leeches. The sea star Luidia (Phylum Echinodermata), hosts the polychaete Podarke among its tube feet. Certain species harvest algae growing on their tubes. Others pop out of their tubes to seize prey. Some trap plankton on a mucus-covered, ciliated eversible proboscis. Filter-feeding marine annelids capture bacteria and feed selectively on sediment particles within tubes (which they build of mucus-cemented sand grains, calcium carbonate, protein and polysaccharide compounds, and other materials) buried in sand or mud. Swimming annelids catch fish eggs or larvae. Many annelids burrow incessantly, turning over and exposing detritus and soil and aerating anaerobic muds and sands these activities are known as bioturbation. The endangered Australian earthworm Megascolides, which is 3 m in length, is the largest species the smallest annelid is only 0.5 mm.Īctive predation or scavenging is the feeding mode for most annelids. Some have colorful gills and cirri, modified parapodia. They may be striped or spotted, and pink, brown, or purple. Chitinous cuticle covers the entire body.Īnnelids live in soil, fresh water, and oceans-including Antarctic seas. Parapodia are unique to polychaetes these thin, fleshy flaps protrude laterally from each body segment. Chitinous lateral bristles called setae on each segment are used for locomotion or to anchor the annelid in substrate or burrow leeches lack setae. Annelids have spacious, mesoderm-lined coeloms-except for leeches, in which tissue packs the coelom-and their coeloms are important in excretion, circulation, and reproduction. Anterior segments bear jaws, eyes, and cirri (singular: cirrus, a slender appendage) in some species the terminal segment may bear a cirrus. Copyright 2002 ETI / Freeman & Co Publishers)Īnnelid worms-polychaetes, earthworms (oligochaetes), and leeches (hirudineans)-are distinguished by linear series of external ringlike segments the grooves between segments coincide with internal compartments, often separated by transverse sheets of tissue (septa), containing serially repeated nervous, muscle, and excretory systems. (To complete all classifications ETI has added the Kingdom and the Phyla of all the different taxa treated on this DVD-ROM without higher classification descriptions.
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