无脊椎动物学/环节动物

 Phylum - Annelid

环节动物，俗称带状蠕虫或分节蠕虫，是一门庞大的门类，拥有 22000 多个现存物种，包括沙蚕、蚯蚓和水蛭。环节动物的生活环境多样，且适应了各种生态环境——一些生活在潮汐带和热液喷口等截然不同的海洋环境中，另一些生活在淡水中，还有一些生活在潮湿的陆地环境中。

  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.