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

Abstract

We describe Zeuxo ezoensis sp. nov. from Hokkaido, Japan. This species closely resembles Z. phytalensis, Z. shitipingensis and Z. turkensis 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 c oxidase subunit I (COI) gene (655 nt) from Z. ezoensis 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 Z. ezoensis within Zeuxo. 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 Zeuxo taxonomy. http://zoobank.org/urn:lsid:zoobank.org:pub:6CB565DB-DAFF-41EF-A06D-EAAE2F619C31.