(Claus, 1863)
Females: In lateral view, R usually curved ventroposteriad; R not tapering uniformly in either lateral or anteroventral views. More characters can be accessed by backtracking the key:
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Males: Ur2 less than 1.35 times as long as segment 2 of P5. More characters can be accessed by backtracking the key:
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Remark: male Clausocalanus mastigophorus is keyed out together with male Claucocalanus parapergens by the same character.