Annelida - Related Animals

...The phylum Stylostomes (about 140 species of sea worms) which has no vascular system, and the phylum Echinostomes (about 145 species of sea worms) which has a closed vascular system, are considered to be intermediate between mollusks and annelids, judging from the nephridia that carry sex cells and the shape of the larvae. (c) They are like mollusks in that they have a secondary coelom, but their bodies are divided into segments, their surface is protected by a hard exoskeleton, and their legs, if any, are very short. The phylum Annelida consists of more than 14,000 species, including lugworms, earthworms, and leeches. Many of them live free in the sea, freshwater, and on land, but some are parasitic.

*Some of the terminology that refers to the phylum "Annelida" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…血管系のない〈星口動物門〉(ホシムシ類約140種，海生)と，閉鎖血管系をもつ〈ユムシ動物門〉(ユムシ類約145種，海生)は，性細胞を運ぶ腎管や幼生の形態から見て，軟体動物と環形動物の中間に位置するものと考えられる。(c)二次体腔がある点は軟体動物に等しいが，体が体節に分かれ，表面が硬い外骨格でまもられていて，足はあってもごく短いもの　〈環形動物門〉はゴカイ，ミミズ，ヒルなど，約1万4000種以上よりなる。海，淡水，陸で自由生活をするものが多いが，寄生性のものもある。…

※「環形動物門」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報