Pleonexes Spence Bate, 1857

Souza-Filho, Jesser F. & Andrade, Luiz F., 2022, A new species of Pleonexes Spence Bate, 1857 (Amphipoda: Senticaudata: Ampithoidae) from the São Pedro and São Paulo Archipelago, Equatorial Atlantic, Brazil, with comments on the genus, Zootaxa 5209 (2), pp. 199-210 : 200-201

Pleonexes Spence Bate, 1857

Pleonexes Spence Bate, 1856: 59 (nomen nudum); 1857: 147. — Conlan, 1982: 2020. — Peart & Ahyong, 2016: 467, Fig. 3I .

Type species. Pleonexes gammaroides Spence Bate, 1857 .

Emended diagnosis. Epistome and upper lip angle directed ventrally, approximately 90° to head ventral margin. Antenna 1 accessory flagellum absent. Mandible molar well developed; palp 3-articulate, weak to stout, article 3 distally smooth. Lower lip outer plate notched, inner lobe shorter than outer lobe. Maxilla 1 palp well developed. Maxilla 2 outer plate broader than inner plate. Coxae long. Gnathopod 1 smaller than gnathopod 2, coxa produced forward anteroventrally, palm acute. Pereopods 3, 4 basis slightly expanded; merus slightly anteriorly expanded. Pereopods 5-7 prehensile. Pereopods 6, 7 propodus subrectangular; distal articles slender. Epimeron 3 without distoventral tooth. Uropod 1 position in situ reaching apices of uropod 2 rami; peduncle distoventral spur reduced, rounded in males, absent in females, setal fringe present, spread along the peduncle; rami of similar length, inner only slightly longer than outer. Uropod 2 peduncle laterodistal projection absent, setal fringe absent. Uropod 3 rami broad; outer ramus with 2 large recurved distal robust setae, denticles present, setal fringe absent. Telson subtriangular or trapezoidal; cusps small to very large; denticles present or absent.

Included taxa. Pleonexes auriculata ( Rabindranath, 1972) ; P. divisura ( Shoemaker, 1933) comb. nov.; P. gammaroides Spence Bate, 1856 ; P. helleri ( Karaman, 1975) ; P. kaneohe (J.L. Barnard, 1970) ; P. kava ( Myers, 1985) ; P. kulafi (J.L. Barnard, 1970) ; P. lowryi sp. nov.; P. maxillissius ( Ledoyer, 1984) ;? P. meganae ( Peart, 2007) ; P. navosa ( Myers, 1985) status nov.; P. parakava ( Peart, 2007) ; P. poipu (J.L. Barnard, 1970) ; P. rotunda ( Peart, 2007) ; P. suapensis ( Correia, Guedes-Silva & Souza-Filho, 2016) comb. nov.

Excluded taxa. Pleonexes koreana ( Kim & Kim, 1988) [removed to Ampithoe ].

Remarks. Pleonexes was resurrected by Peart & Ahyong (2016) based on some differences from Ampithoe : presence of a rounded and reduced spur on the peduncle of uropod 1 in males, subtriangular telson with sometimes large cusps, expanded bases and meri of pereopods 3–4, and prehensile pereopods 5–7. Based on these characters, some species were transferred from Ampithoe to Pleonexes . However, A. divisura Shoemaker, 1933 from Tortugas (Florida), which fits well with these characters ( Serejo & Licínio 2002), was not included in Peart & Ahyong (2016) ’s analysis. Thus, we transfer it from Ampithoe to Pleonexes . Ampithoe suapensis Correia, Guedes-Silva & Souza-Filho, 2016 described from Pernambuco ( Brazil) is also transferred to Pleonexes , because of the presence of important diagnostics characters of Pleonexes .

Pleonexes kaneohe navosa Myers, 1985 was described as a subspecies of P. kaneohe (J.L. Barnard, 1970) due to its more elongated carpus of gnathopod 2 and the presence of robust setae on the anterior margin of the pereopod 5 basis. However, we detected more differences in the subspecies ( P. kaneohe in parentheses): male gnathopod 1 coxa with slightly produced anteroventral lobe (vs. strongly produced); gnathopod 2 basis with only one slender setae (vs. a tuft of long slender setae), carpus elongated (vs. short), lobe rounded (vs. subacute), propodus setose on anterodistal angle (vs. inner surface), palm serrate, sinuose with a distinct hump defining palm (vs. not serrate, evenly rounded and not defined) and telson subtrapezoidal with truncate apex (vs. subtriangular with subacute apex). Therefore, we raise this subspecies to full species rank, Pleonexes navosa ( Myers, 1985) .

Furthermore, P. koreana ( Kim & Kim, 1988) , originally described as Ampithoe , lacks the distoventral spur in male uropod 1 peduncle and the pereopods 5–6 are not prehensile, so we transfer it back to Ampithoe . In P. meganae ( Peart, 2007) , it is doubtful to place correctly in Pleonexes , because of no description or illustrations of the pereopods 6–7 and uropod 1 in the original publication. Even if we consider the characters used in her key to identify P. meganae ( Peart, 2007, p. 6-7), because she stated in the first step: “Uropod 1 distoventral spur present, rounded and reduced in male and absent in female; pereopods 5–7 prehensile; telsonic cusps large”, in her description and illustration only female pereopod 5 was given and the telsonic cusp are very small.

In order to facilitate the species comparison, we divide the genus into 3 groups based on the telson morphology. Group 1—Apex truncate and cusps large (two hooks)— P. gammaroides , P. helleri , P. poipu .

Group 2—Apex truncate and cusps small— P. auriculata , P. navosa status. nov., P. meganae , P. parakava , P. rotunda and P. suapensis comb. nov.

Group 3—Apex subacute and cusps small or vestigial— P. divisura comb. nov.; P. kaneohe , P. maxillissius ; P. lowryi sp. nov., P. kava and P. kulafi .

Figures

FIGURE 3. Pleonexes lowryi sp. nov. Holotype, male, 6 mm, São Pedro and São Paulo Archipelago, 00°55’N 29°20.7’W, Brazil, MOUFPE 15519; paratype, female, 4.8 mm, same data as holotype, MOUFPE 15520. Scale bars: 0.3 mm.