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Which animals belong to the phylum Annelida?
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annelid
The structure of polychaetes. (Left) Free-moving polychaetes. (A) Neanthes, (B) Nereis. (Right) Tube-dwelling (sedentary) polychaetes. (C) Amphitrite, (D) Sabella.
The phylum Annelida consists of invertebrate animals characterized by segmented bodies, a coelom, and typically, movable bristles known as setae. There are more than 9,000 known species, which are categorized into three primary classes:1
- Marine worms (Polychaeta): This diverse group includes both free-moving species and sedentary, tube-dwelling forms. Examples include the scale worm (Halosydna), the sea mouse (Aphrodita), and the oyster pest Polydora.12
- Earthworms (Oligochaeta): These annelids are generally adapted to terrestrial or freshwater environments.12
- Leeches (Hirudinea): These specialized annelids typically lack setae and have a reduced coelom. They are closely related to oligochaetes, sharing features such as the clitellum.12
Would you like to learn more about the specific anatomical differences between these three classes?