Reconstruction of arietellid copepod phylogenetic relationship, with description of a new species of Sarsarietellus (Copepoda, Calanoida, Arietellidae) from Korean waters.

A new species of the genus Sarsarietellus from Korean waters, S. orientalis n. sp. is described based on both sexes. This is very closely related to S. suluensis Ohtsuka, Nishida and Machida, 2005 , but is readily distinguished by the following characteristics: in the female (1) narrow head; (2) nearly symmetrical posterior corners of last pedigerous somite, not extending beyond the genital double-somite; (3) antennary endopod slightly longer than the exopod; (4) nearly equal length of three outer spines and the terminal spine of the exopod of the fifth leg, except for the proximal third outer spine; and in the male the left fifth leg with two whip-like setae on the tip of the second exopodal segment not being rotated outside. Sarsarietellus orientalis is the fourth species of the genus Sarsarietellus, while the male of Sarsarietellus species is the first reported. The habitat colonization of arietellids is reconsidered.