A new species of <i>Zeuxo</i> (Crustacea: Peracarida: Tanaidacea) from Japan, with remarks on carapace pigmentation as a potentially useful taxonomic character

We describe <i>Zeuxo ezoensis</i> sp. nov. from Hokkaido, Japan. This species closely resembles <i>Z. phytalensis</i>, <i>Z. shitipingensis</i> and <i>Z. turkensis</i> in having the pleopodal endopod with one inner plumose seta, maxillipedal palp article 4 with one outer simple seta, the left mandible with a wide, denticulate lacinia mobilis and one bifurcate accessory seta, and the right mandible with a peg-like lacinia mobilis and two accessory setae. It differs from them in having (1) antennal article 6 longer than wide, (2) the distal region of the maxillipedal endite with four spiniform setae and two circumplumose setae, (3) maxillipedal palp article 2 with one outer simple seta, (4) the chelipedal carpus with three or four dorsodistal simple setae, (5) the chelipedal dactylus with one inner simple seta, (6) the pereopod-1 basis with one or two ventrodistal simple setae, (7) the pereopod-1 carpus with one ventrodistal simple seta, and (8) the uropod with four or five articles (basal article plus three or four ramus articles). Partial nucleotide sequences for the cytochrome <i>c</i> oxidase subunit I (COI) gene (655 nt) from <i>Z. ezoensis</i> specimens from four localities in Hokkaido showed Kimura 2-parameter (K2P) divergences of 0–0.5% and 0.6–1.5% within and between populations, respectively. Based on the COI data, we examined the phylogenetic position of <i>Z. ezoensis</i> within <i>Zeuxo</i>. Six specimens used for morphological observations and 10 specimens used for COI sequencing showed a similar dorsal pigmentation pattern on carapace. We briefly discuss the validity of using this pattern as a diagnostic character in <i>Zeuxo</i> taxonomy. http://zoobank.org/urn:lsid:zoobank.org:pub:6CB565DB-DAFF-41EF-A06D-EAAE2F619C31