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How many annelid species are known?
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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.
There are more than 9,000 known species of annelids, which are a major phylum of invertebrate animals. These species are distributed among three primary classes: marine worms (Polychaeta), earthworms (Oligochaeta), and leeches (Hirudinea).1