Annelida

Annelida is an animal phylum whose members typically have bodies divided into repeated segments. It includes earthworms, leeches, and marine bristle worms.

Metamerism: The division of an animal body into repeated structural units along its length. Repeated segments are the defining feature of most annelid bodies.
Hydrostatic skeleton: A support system in which muscles act against pressure within a fluid-filled body cavity. Segmental coelomic compartments provide the pressure that powers many annelid movements.
Earthworm: A burrowing annelid that feeds on soil and decaying organic matter. Earthworms illustrate segmented locomotion and soil-based feeding.
Jean-Baptiste Lamarck: A French naturalist who developed an early theory of species change and helped establish invertebrate classification. Lamarck introduced the name Annelida for the segmented worms in the early nineteenth century.
Vermicomposting: The use of earthworms to convert organic waste into nutrient-rich compost. Earthworm feeding and burrowing drive the decomposition used in this practice.
Coelom: A fluid-filled body cavity completely lined by mesoderm. Annelids typically use this cavity as a hydrostatic skeleton and space for organs.
Peristalsis: The movement of a body or substance through coordinated waves of muscle contraction. Earthworms advance through soil using alternating contractions along their segmented bodies.
Leech: A flattened annelid, usually without chaetae, that moves with suckers; some species feed on blood. Leeches are specialized clitellates whose body plan supports attachment and looping movement.
Clitellata: A group of annelids that includes earthworms and leeches and bears a clitellum during reproduction. This group unites familiar terrestrial and freshwater forms within the phylum.
Soil ecology: The study of interactions among organisms and their physical environment in soil. Earthworms alter soil structure, nutrient cycling, and habitats for other organisms.

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