Sextonia Chevreux, 1920

Labay, Vjacheslav S., 2017, A new species of Sextonia Chevreux, 1920 (Crustacea: Amphipoda: Liljeborgiidae) from the Okhotsk Sea, Zootaxa 4353 (3) : -

Sextonia Chevreux, 1920

Sextonia — Chevreux, 1920: 76.— Chevreux & Fage, 1925: 159.— Karaman, 1980: 431.— Barnard & Karaman, 1991: 417.— d'Udekem d'Acoz, 2010: 150.

Diagnosis. See d'Udekem d'Acoz (2010).

Species composition. Sextonia contains two species Sextonia longirostris Chevreux, 1920 and Sextonia caecus sp. nov.

Remarks. The genus Sextonia exhibits several characters, which are unique for the Liljeborgiidae : molar process well developed, fully triturative, with flat grinding surface and a single posterior gnathobasic seta; article 1 of mandibular palp with setae; article 3 of mandibular palp with several setae on anterior margin; carpus of gnathopod 1 very short, with minute narrow posterior process, propodus much longer than in pereopod 2; carpus of gnathopod 2 very long, longer than propodus; peduncle of uropod 1 with several ventrofacial spines, a proximal ventral seta on the inner ramus of uropod 1. Despite these exceptional characters, several authors ( Barnard 1959, Imbach 1967, Karaman 1979) considered Sextonia as a junior synonym of Idunella G.O. Sars, 1894 . While the affinities of Sextonia with Idunella are unequivocal, unique characteristics of the mandible morphology have been considered by Karaman (1980), J. L. Barnard & Karaman (1991) and d'Udekem d'Acoz (2010) as sufficient to accept the validity of Sextonia . Following the listed authors, I consider the allocation of the separate genus Sextonia to be justified.

Before the discovery of a new species, the genus Sextonia was represented by the only species S. longirostris . S. longirostris is found in the North East Atlantic from North West France to the Atlantic coast of Morocco. It inhabits well-sorted fine sands from intertidal to 34 m (see the rewiew of d'Udekem d'Acoz [2010]). The new species is found in the North West Pacific Ocean at the depth range of 109–309 m, which significantly expands the notion about biogeography and ecology of the genus Sextonia .