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Annelids. Annelid Taxonomy. Kingdom Animalia Phylum Annelida Class Oligochaeta Class Hirudinea Class Polychaeta. Characteristics of Annelids. Segmented body Coelom (body cavity) Organ systems Bristles of Parapodia (appendages) Bilateral symmetry Cerebral Ganglion (brain).
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Annelid Taxonomy • Kingdom Animalia • Phylum Annelida • Class Oligochaeta • Class Hirudinea • Class Polychaeta
Characteristics of Annelids • Segmented body • Coelom (body cavity) • Organ systems • Bristles of Parapodia (appendages) • Bilateral symmetry • Cerebral Ganglion (brain)
Form and Function • Annelids, also known as segmented worms, are round, wormlike animals with long, segmented bodies. • An annelid’s segments are very similar to on another and are separated by internal partitions. • In many annelids, bristles called setae are attached to each segment.
Feeding • The digestive tract, or gut, is a long tube within the body cavity of the worm that extends from the mouth to the anus. • Food enters through the mouth and travels through the gut, where it is digested.
Feeding • Like mollusks, annelids have evolved structures and behaviors that allow them to use a wide variety of foods. • Annelids range from filter feeders to predators
Respiration • Aquatic annelids breathe through gills. • Land annelids take in oxygen and give off carbon dioxide through diffusion.
Internal Transport • Annelids typically have closed circulatory systems organized around two blood vessels that run the length of their bodies. • Blood in the top (dorsal) vessel moves toward the head of the worm.
Internal Transport • Blood in the bottom (ventral) vessel moves from the head to the tail. • The dorsal blood vessel functions like a heart because it contracts rhythmically.
Excretion • Solid wastes pass out through the anus at the end of the gut. • Cellular wastes containing nitrogen are eliminated by the nephridia. • The nephridia are excretory organs that filter fluid in the coelom.
Response • Many annelids have well developed nervous systems consisting of a brain and several nerve cords. • The sense organs are best developed in the free-living marine annelids. • Many of these species have sensory tentacles, chemical receptors, statocysts to detect gravity, and two or more pairs of eyes.
Movement • Annelids have two groups of body muscles. • Longitudinal muscles run from the front to rear of worm and can contract to make wormer shorter and fatter. • Circular muscles wrap around each body segment and can contract to make the worm longer and thinner.
Movement • Earthworms move by alternating contractions of these two sets of muscles, using its setae to prevent slipping. • Burrowing annelids use their muscles to force their way through sediment. • Marine annelids have paddle-like appendages called parapodia on each segment, which they use for swimming and crawling.
Reproduction • Most annelids reproduce sexually. • Some species use external fertilization and have separate sexes. • Other annelids are hermaphrodites. • Individuals rarely fertilize their own eggs. Two worms attach to each other and exchange sperm. • Fertilization occurs at the clitellum.
Class Oligochaeta • Comes from Greek words: • Oligos – few • Chaite - hairs • Contains earthworms and their relatives. • Annelids that typically have streamlined bodies and relatively few setae.
Class Oligochaeta • Most oligochaetes live in soil or fresh water. • Tubifex worms are red, threadlike aquatic worms that are sold in pet stores as fish food.
Class Oligochaeta • Earthworms moves through soil, sucking in detritus and soil and passing it through its digestive system. • Undigested organic material is passed out through anus, producing castings. • Some tropical earthworms produce castings 18 cm long and 2 cm thick.
Class Hirudinea • Leeches • Leeches are typically external parasites that suck the blood and body fluids of their hosts. • One fourth of all leeches are carnivores that feed on soft-bodied invertebrates.
Class Hirudinea • Leeches have powerful suckers on both ends to help them cling to hosts. • Some slice into the skin with razor sharp jaws. • Once the wound has been made, leeches use their pharynx to suck in blood,
Class Hirudinea • Some leeches release a substance that anesthetizes the wound, to keep the host from knowing it has been bitten. • Leeches were once commonly used to treat medical conditions.
Class Hirudinea • Currently doctors use leeches to reduce swelling after surgery. • Leeches also produce anti-clotting chemicals.
Class Polychaeta • Comes from Greek words: • Poly – many • Chaite - hairs • Contains sandworms, bloodworms, and their relatives. • Polychaetes are marine annelids that have paired, paddle-like appendages typed with setae.
Class Polychaeta • Polychaetes live in cracks and crevices in coral reefs; in sand, mud, and piles of rocks; or even out in the open water. • Some burrow through or crawl over sediment.
