無脊椎動物學/環節動物

 Phylum - Annelid

環節動物，俗稱帶狀蠕蟲或分節蠕蟲，是一門龐大的門類，擁有 22000 多個現存物種，包括沙蠶、蚯蚓和水蛭。環節動物的生活環境多樣，且適應了各種生態環境——一些生活在潮汐帶和熱液噴口等截然不同的海洋環境中，另一些生活在淡水中，還有一些生活在潮溼的陸地環境中。

  The annelids are bilaterally symmetrical, triploblastic, coelomate, invertebrate organisms. They also have parapodia for locomotion. Most textbooks still use the traditional division into polychaetes (almost all marine), oligochaetes (which include earthworms) and leech-like species. Cladistic research since 1997 has radically changed this scheme, viewing leeches as a sub-group of oligochaetes and oligochaetes as a sub-group of polychaetes. In addition, the Pogonophora, Echiura and Sipuncula, previously regarded as separate phyla, are now regarded as sub-groups of polychaetes. Annelids are considered members of the Lophotrochozoa, a "super-phylum" of protostomes that also includes molluscs, brachiopods, and nemerteans.