Pseudomimonectes robustus Vinogradov, 1960

Zeidler, Wolfgang, 2012, A review of the hyperiidean amphipod families Mimonectidae and Proscinidae (Crustacea: Amphipoda: Hyperiidea: Scinoidea) 3533, Zootaxa 3533, pp. 1-74 : 53-55

Pseudomimonectes robustus Vinogradov, 1960

( Fig. 27)

Pseudomimonectes robustus Vinogradov, 1960: 219–222 , figs. 12–13. — Bowman & Gruner 1973: 11–12, fig. 12. Vinogradov et al. 1982: 110–112, figs. 44–45. Vinogradov & Vinogradov 2006: 62. Mori et al. 2010: 8 (list).

Type material. This species was described from one, immature specimen (sex unknown), 4.5 mm in length, from the Pacific Ocean, in the Ryukyu Trench (27°49’S 130°37’W), Vityaz stn. 3528, 4080– 5500 m, 28 October 1958. The unique holotype is in the ZMMU (Mb-1061).

Diagnosis. According to Vinogradov (1960) and Vinogradov et al. (1982). Known only from the unique holotype. Pereon slightly inflated. Antennae 1 relatively robust; about as long as head and first 2.5 pereonites combined (medially). Antennae 2 much reduced, consisting of four small articles; as long as peduncle of A1. Gnathopod 1; basis almost as long as remaining articles combined; carpus with broad distal margin, slightly shorter than propodus; dactyl short, curved. Gnathopod 2 slightly longer and more slender than G1; otherwise similar in structure. Pereopods 3 & 4 similar in structure and length; basis length equal to merus and carpus combined; merus length about two-thirds carpus; propodus slightly longer than carpus; dactyl relatively strong, curved, length about 0.2x propodus. Pereopod 5 sub-equal in length to P4 and more slender; basis with slight bulge mid-way on distal margin, length about 1.7x merus; carpus slightly longer than merus and propodus; merus and propodus similar in length; dactyl relatively strong, marginally longer than 0.2x propodus. Pereopod 6; length about 0.8x P5; basis length about 1.8x merus; carpus slightly longer than merus; propodus as long as carpus, with slight bulge mid-way on anterior margin; dactyl relatively strong, curved, length about 0.3x propodus. Pereopod 7 with relatively broad articles; length about 0.8x P6; basis about twice as long as wide, almost 3x length merus; carpus bulging anteroproximally, narrowed distally, about 1.6x length merus; propodus slightly longer and more slender than carpus, with slight bulge mid-way on anterior margin; dactyl strong and falcate, length almost one-third propodus. Uropoda with slender, but not particularly lanceolate rami, with rounded tips. Uropod 1; inner ramus length twice outer, similar in length to peduncle. Uropod 2; inner ramus length 1,8x outer, marginally longer than peduncle. Uropod 3; inner ramus length almost 1.4x outer, as long as peduncle; peduncle width 0.4x length. Telson ovaltriangular, length marginally more than one-third peduncle of U3.

Colour not known for living specimen.

Remarks. I have not seen any specimens of this species and have been unable to examine the unique holotype, but accept its validity based on the observations of Vinogradov (1960).

The one-articulate palp, and relatively broad lacinia mobilis of the mandibles, readily distinguishes this species, and the genus, from other members of the family. Otherwise it is very similar to Mimonectes . In having simple gnathopods and relatively strong dactyls, it resembles M. spandlii , but is readily distinguished by the relatively longer merus of pereopods 3–6. It is also similar to M. colemani , but in that species the dactyls are not as strong, and that of pereopod 7 is not falcate, and pereopods 6 & 7 lack the bulge mid-way on the anterior margin of the propodus. The structure of pereopod 7 is also similar to M. alexanderi , and initially I thought that this species might also belong to Pseudomimonectes but the mandibles lack the characteristic one-articulate palp (fig. 27).

Distribution. Known only from the type locality, from the unique holotype, as detailed above.