Crayfish earthworm (English name) Stephanodrilus sapporensis

Japanese: ザリガニミミズ（英語表記）Stephanodrilus sapporensis

A member of the phylum Annelida, class Oligochaeta, order Neolithicida, family Oligochaeidae. Body length 9-12 mm, body width 2-3 mm. The body is cylindrical, with a head and body, and 10 major segments. None of the segments have setae. The mouth at the anterior end of the body is surrounded by 16 projections, and on the outside of that is a dorsal lip with 13 finger-like projections. The oral cavity also has two chitinous jaw plates, the shape of which varies depending on the species. It is hermaphroditic, with one male pore opening on the midline of the ventral surface of the sixth major segment. It has a sucker at the posterior end of its body, which it uses to attach itself to the surface of Hokkaido crayfish and move in a similar way to a leech. The egg capsules are mainly attached to the swimming legs of the crayfish. In addition to this species, more than a dozen other species, such as the Kamuri crayfish worm and the Ooago crayfish worm, are known to be found on the surface of the bodies and in the gill chambers of crayfish from northern Honshu and Hokkaido, but all of these are small, with body lengths of 2 to 3 mm. One or two species of crayfish worms are also found attached to American crayfish that have naturalized from the United States. Recently, they have also been found on crustaceans other than crayfish.

Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information

Japanese:

環形動物門貧毛綱新貧毛目ヒルミミズ科。体長9～12mm，体幅2～3mm。体は円柱形で，頭部と胴部に区別され，10大体節から成る。各体節には剛毛がない。体前端の口の周囲には 16個の突起が並び，その外側に 13個の指状突起をもった背唇がある。また口腔内にはキチン質の2個の顎板があり，その形は種類によって異なる。雌雄同体で，第6大体節の腹面中央線上に1個の雄性孔が開く。体の後端に吸盤をもち，これで北海道産のザリガニの体表に付着して生活し，ヒルと同じような運動をする。卵包はおもにザリガニの遊泳脚に固着している。なお，本種のほかにカムリザリガニミミズ，オオアゴザリガニミミズなど十数種類が本州北部や北海道産のザリガニの体表，鰓室内から知られているが，これらはいずれも体長2～3mmで小さい。アメリカから帰化したアメリカザリガニにも1～2種類のザリガニミミズが付着している。最近，ザリガニ以外の甲殻類からも発見されている。

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