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The Class Oligochaeta

The Class Oligochaeta - to internal septa(walls separating...

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The Class Oligochaeta The class Oligochaeta includes earthworms, that tend to have their few setae protruding in clusters directly from their body. Earthworms have poorly developed heads or parapodia. Locomotion is by coordinated movement of the body muscles and assistance of their setae. When longitudinal muscles contract, segments bulge and setae protrude and anchor into the soil. Circular muscles contract, causing the worm to lengthen, setae are withdrawn and the segment moves forward. Earthworms reside in moist soil where a moist body wall facilitates gas exchange. Earthworms are scavengers that extract organic remains from the soil they eat. A muscular pharynx draws food into the mouth. Ingested food is stored in a crop and ground up in a muscular gizzard. The dorsal surface of the intestine is expanded into a typhlosole that allows more surface area for digestion. External segments correspond
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Unformatted text preview: to internal septa (walls) separating each body segment. The earthworm excretory system has coiled nephridia tubules in each segment with two openings: one is a ciliated funnel that collects coelomic fluid, and the other is an exit in the body wall. Between the two openings, the coiled nephridia tubule allows removal of waste materials from blood vessels. Red blood is moved anteriorly by a dorsal blood vessel and pumped by five pairs of hearts (sometimes referred to as aortic arches) to a ventral vessel. Earthworms are hermaphroditic, having both testes with seminal vesicles, and ovaries with seminal receptacles. Mating involves the worms lying parallel to each other facing opposite directions and exchanging sperm. Each worm possesses a clitellum that then secretes a mucus, protecting sperm and eggs from drying out. Embryonic development lacks a larval stage....
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