Pseudonesimus Chevreux, 1926

Kilgallen, N. M. & Lowry, J. K., 2014, The Tryphosa group (Crustacea: Amphipoda: Lysianassoidea: Lysianassidae: Tryphosinae), Zootaxa 3768 (5), pp. 501-545 : 511

Pseudonesimus Chevreux, 1926

Pseudonesimus Chevreux, 1926: 3 .— Chevreux, 1935: 13.—J.L. Barnard, 1961: 50.

Aristiopsis J.L. Barnard, 1961: 30 .―J.L. Barnard, 1969: 299, 306, 310, 311, 314 (key), 324.― Barnard & Karaman, 1991: 467. (type species Aristiopsis tactius J.L. Barnard, 1961 , original designation).

Schisturella .―J.L. Barnard, 1969: 361 (in part).― Barnard & Karaman, 1991: 526 (in part).

Type species. Pseudonesimus abyssi Chevreux, 1926 , by monotypy.

Included species. Pseudonesimus includes seven species: P. abyssi Chevreux, 1926 ; P. cedrosianus (J.L. Barnard, 1967) ; P. parachelatus ( Ledoyer, 1986) ; P. robustus (J.L. Barnard, 1961) ; P. tacitus (J.L. Barnard, 1961) ; P. tasmanensis J.L. Barnard, 1961 ; P. zopa (J.L. Barnard, 1966) .

Diagnostic description. Antenna 1 flagellum article 1 lacking robust seta on distal margin; accessory flagellum forming cap. Antenna 2 flagellum articles 3–5 slender in female and (?) male, with weak brush setae on the anterior margin or brush setae absent. Mandibular incisor curved; molar with reduced column and convex triturating surface (button); palp attached midway. Maxilla 1 ST-7 serrate along the distomedial margin; ST-D slender, apically cuspidate. Maxilliped outer plate with apical robust setae. Gnathopod 1 subchelate; coxa vestigial; carpus subequal or slightly longer than propodus; propodus palm transverse, convex. Pereopod 4 coxa with well developed posteroventral lobe. Uropod 2 inner ramus constricted. Uropod 3 rami without plumose setae. Telson moderately to slightly cleft.

Remarks. Pseudonesimus was originally described by Chevreux (1926) to accommodate the north Atlantic species Pseudonesimus abyssi . Aristiopsis was later described by Barnard (1961) for Aristiopsis tacitus . Barnard did not associate A. tacitus with Pseudonesimus , and did not draw any comparison between the two genera in his assessment of their relationships with other taxa. Thus, Pseudonesimus remained a monotypic genus (with two subspecies) for more than 40 years until it was eventually placed in the synonymy of Schisturella by Barnard (1967) where it has since remained.

Based on the lack of a robust seta on the distal margin of antenna 1 flagellum article 1, the relative length of the gnathopod 1 carpus and propodus, the strongly subchelate, transverse and convex gnathopod 1 palm, and the cleftness of the telson we consider Pseudonesimus to be distinct from Schisturella , and congeneric with Aristiopsis . In accordance with the Principle of Priority ( ICZN 1999: Article 23) Aristiopsis thus becomes a junior synonym of Pseudonesimus .

Distribution. Atlantic and Pacific Oceans.