Annelids: Segmented Worms, Classes, and Key Structures

Annelids

Segmented worms with repeating body sections.

Septa

Internal walls that divide the body into segments.

Setae

Tiny bristle-like structures used for movement and grip.

Coelom

Fluid-filled body cavity surrounding organs.

Longitudinal muscles

Muscles that run lengthwise; contraction shortens the body.

Circular muscles

Muscles around the body; contraction lengthens the body.

Hydrostatic skeleton

Support system using fluid pressure to help movement.

Peristaltic movement

Wave-like muscle contractions that move the organism forward.

Polychaeta

Class of marine annelids with many setae.

Parapodia

Paddle-like structures for movement and gas exchange.

Tentacular crown

Crown of tentacles used for feeding.

Atoke

Non-reproductive form of a polychaete.

Epitoke

Reproductive form filled with gametes.

Pogonophorans

Tube-dwelling worms that rely on symbiotic bacteria instead of a digestive system.

Oligochaeta

Class of annelids (like earthworms) with few setae.

Clitellum

Thickened band that secretes mucus for reproduction.

Pharynx

Muscular structure that pulls in food.

Crop

Storage chamber for food.

Gizzard

Organ that grinds food.

Cocoon

Protective case where fertilized eggs develop.

Hirudinida

Class of annelids that includes leeches.

Cerebral ganglia

Simple brain that controls basic functions.

Anticoagulant

Substance that prevents blood from clotting.

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