Metarhachotropis, Ariyama & Kohtsuka, 2022

Ariyama, Hiroyuki & Kohtsuka, Hisanori, 2022, Metarhachotropis parva, a new genus and species of Eusiridae (Crustacea: Amphipoda) from Sagami Bay, central Japan, Zootaxa 5188 (1), pp. 95-100 : 96

Genus Metarhachotropis , new

[Japanese name: Kawari-ryūgūyokoebi-zoku, new]

Type species. Metarhachotropis parva sp. nov. by monotypy.

Diagnosis. Body weakly compressed laterally, smooth. Head massive, rostrum large, eyes present. Antennae subequal, without calceoli, accessory flagellum 1-articulate, flagella short. Mandible, molar poorly triturative. Maxillae reduced, palp of maxilla 1 ordinary, maxilla 2 inner plate broader than outer plate. Coxae very short, coxa 1 strongly produced anteriorly, coxa 4 lacking posterior excavation, coxae 5, 6 bilobed. Gnathopods alike, large, subchelate, not eusirid form; carpi narrow, with posterior lobe; propodi ovate, much longer than carpi, palms oblique. Pereopods slender; pereopods 3, 4 similar, bases narrow; pereopods 5–7 progressively longer, bases expanded. Pleonal epimeron 3 rounded. Uropods biramous, outer rami shorter than inner rami. Telson elongate, cleft.

Etymology. From the Greek meta (= beyond) and Rhachotropis (related genus).

Remarks. Metarhachotropis gen. nov. is characterized by the massive head with large rostrum. Despite the unique body shape, the keys to families in Barnard & Karaman (1991) lead the present specimens to Eusiridae sensu lato owing to (1) head massive but not downturned; (2) accessory flagellum 1-articulate; (3) mandibular palp present, molar well developed; (4) coxae 1–3 almost same length; (5) urosomites separate; (6) uropod 3 biramous, peduncle short, inner ramus not reduced; and (7) telson flat, elongate and cleft. Within the genera of the family, only Eusirella Chevreux, 1908 and Rhachotropis Smith, 1883 [both included in Eusiridae sensu stricto ( Lowry & Myers 2017)] resembles this new genus in the very short coxae and the strongly produced coxa 1. However, Metarhachotropis can be distinguished from Eusirella by the large rostrum (small in Eusirella ) and the ordinary length of the maxilla 1 palp (short in Eusirella ), and from Rhachotropis by the smooth body (carinate or toothed in Rhachotropis ).

Included taxa. Metarhachotropis parva sp. nov.