Pleonexes lowryi, Souza-Filho & Andrade, 2022

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 : 201-208

Pleonexes lowryi sp. nov.

( Figs 1–7 )

urn:lsid:zoobank.org:act:A233A7CE-F0CA-4A01-8B39-188D29A111AD

Material examined. Holotype: male, 6.0 mm, dissected and drawn, São Pedro and São Paulo Archipelago, 00°55’N 29°20.7’W, Rio Grande do Norte state, Brazil, November 2004, MOUFPE 15519 . Paratypes: 1 female, 4.8 mm, dissected and drawn, same data as holotype, MOUFPE 15520 ; 6 males, same data as holotype, MOUFPE 15524 . Other material. One female, 5.4 mm and 1 male, 5.8 mm, used for SEM images, same data as holotype (lost by fire in the Museu Nacional) .

Type locality. São Pedro and São Paulo Archipelago, Equatorial Atlantic, Brazil .

Etymology. The species is named in honor to the late James K. Lowry for his huge contribution to the recent Amphipoda systematics.

Diagnosis. Mandibular palp slender, poorly setose. Gnathopod 1 carpal lobe rounded; propodus longer than carpus, palm entire, with a robust seta defining palm. Gnathopod 2 basis anterodistal lobe large and rounded; propodus longer than carpus, palm strongly acute, entire, occupying almost entire posterior margin, densely setose. Pereopods 3–4 basis slightly expanded. Pereopods 5–7 strongly prehensile. Uropod 1 peduncle with short and blunt spur in male, setal fringe weak, composed of 5 long and slender setae. Uropod 3 peduncle with 2 distal robust setae, outer ramus subequal to inner ramus, with a patch of small conical lateral denticles; inner ramus with 2 distal robust setae. Telson subtriangular, with one small subdistal lobe on each side.

Description. Based on Holotype male, 6.0 mm, MOUFPE 15519. Head almost as long as deep. Antenna 1 poorly setose, shorter than antenna 2, accessory flagellum absent. Antenna 2 peduncle strong, poorly setose, article 4 shorter than 5 (0.8 x); flagellum shorter than peduncle (0.56 x). Upper lip ventral margin rounded and weakly pubescent. Mandible molar well developed; incisor 7-dentate, both right and left; lacinia mobilis large, 7 or 8-dentate (left and right, respectively); accessory setal row consisting of 3 or 4 setae (left and right, respectively); palp slender, article 2 longer than article 3 (1.7 x), bearing a slender seta subdistally (left); article 3 longer than article 1 (2.0 x), with 2 slender setae apically. Lower lip, with lateral lobe longer than medial lobe, outer plate notched, mandibular lobe subacute apically, with curved margins. Maxilla 1, inner plate with a short slender seta; outer plate with 8 robust setae, being one stout and smooth on outer distal angle seta and 7 robust and dentate setae; palp with 3 apical robust setae and 4 marginal slender setae. Maxilla 2, inner plate narrower than outer. Maxilliped outer plate with reduced setation (7 small robust setae and 6 slender setae).

Pereon. Gnathopod 1, coxa almost as deep as gnathopod 2 coxa, anteroventral corner slightly produced, distoventral margin rounded, anterior margin almost straight, ventral margin with a row of small setules; basis longer than coxa, anterodistal lobe moderate and rounded, with 3 slender setae, posterodistal corner with 2 slender setae; merus posterior margin with 7 slender setae; carpus slightly longer than merus, subtriangular, anterior margin with a slender seta in middle and 2 setae on anterodistal corner, posterior margin poorly lobate and setose; propodus narrow (length 2.4 x width), suboval, palm with 1 striate robust seta each on near hinge of dactylus and end of palm; dactylus inner margin denticulate. Gnathopod 2, coxa ventral margin with a row of small setules; basis longer than coxa, without setae on posterior margin; merus forming a short setose lobe distoventrally, anterior margin with a seta; carpus subequal in length to merus, subtriangular, anterior margin without setae; posterior margin lobate and setose; propodus broad (length 1.9 x width), ovoid, posterior margin to medial surface densely setose, palm strongly acute, slightly concave, with 1 striate robust seta each on near hinge of dactylus and end of palm; dactylus strongly curved proximally, acute, inner margin denticulate. Pereopods 3–4, similar to each other, merus narrow and subquadrate. Pereopod 5, coxa lobate posteriorly; basis without marginal slender setae; ischium–dactylus slender; propodus slightly expanded distally, subrectangular, with 4 distal striated robust setae (distal one strongly curved); dactylus strongly curved, striated, with unguis on tip. Pereopods 6, coxa bilobate, anteroventral lobe deeper; basis without marginal slender setae; ischium–dactylus slender; propodus slightly expanded distally, subrectangular, with 4 distal striated robust setae (distal one strongly curved); dactylus strongly curved, striated, with unguis. Pereopod 7, coxa wider than deep; basis with sparse marginal slender setae; ischium–dactylus slender; propodus not expanded distally, subrectangular, with only slender setae, prehensile; dactylus strongly curved, striated, with unguis.

Pleon. Epimeral plates 1–3, posteroventral corner rounded. Uropod 1 peduncle with 3 dorsomedial, 4 dorsolateral and 1 ventrolateral robust setae; outer ramus with 2 marginal robust setae and 2 apical robust setae; inner ramus with 3 marginal robust setae and 4 apical robust setae. Uropod 2 peduncle with 3 robust setae, setal fringe absent; outer ramus shorter than inner ramus, with 3 marginal robust setae and 3 apical robust setae; inner ramus with 5 marginal and 4 apical robust setae. Uropod 3 peduncle longer than broad (2.2 x width), longer than both rami (2.2 x), with 1 marginal slender setae and 2 robust and 6 distal slender setae; outer ramus lacking marginal robust setae; inner ramus with 1 distal robust seta and 4 slender setae. Telson with a pair of dorsal long setae and 4 marginal and slender setae on each side, apex with denticles.

Female (sexually dimorphic characters). Based on paratype female, 4.8 mm, MOUFPE 15520. Antenna 2 weak. Gnathopod 1 slightly smaller than gnathopod 2; coxa subequal in size to gnathopod 2 coxa; basis shorter than coxa; carpus shorter than propodus (0.65 x); propodus subrectangular; palm with 1 striate robust seta each on near hinge of dactylus and end of palm. Gnathopod 2, basis posterodistal lobe rounded, with 4 slender setae; merus truncate distally, not forming a lobe; carpus subequal in length to merus, shorter than propodus (0.5 x); propodus oval (length 1.98 x width); palm with 1 striate robust seta each on near hinge of dactylus and end of palm. Uropod 1 penducle lacking distovental spur.

Remarks. The characters of the new species described herein fit well the emended diagnosis shown above. Within the group 3 (telson with subacute apex and small or vestigial cusps), Pleonexes lowryi sp. nov. is close to P. kaneohe from Hawaii in having the not-defined palm of male gnathopod 2. However, it can be distinguished by the following combination of characters ( P. kaneohe in parentheses): gnathopods 1–2 basis lacking long setae on posterior margin (vs. with tuft of long setae), palm of male gnathopod 2 with 1 robust seta each on near hinge of dactylus and end of palm (vs. lacking robust setae); and propodus of pereopod 7 different from pereopods 5–6, distally slender, without palm and robust setae (vs. prehensile, similar to pereopods 5–6, distally expanded, with palm and robust setae).

Geographic distribution. Known only from the type locality.

Habitat. Depth 1– 2 m. Attached to green algae Caulerpa spp.

Figures

FIGURE 1. Pleonexes lowryi sp. nov. male, 5.8 mm, São Pedro and São Paulo Archipelago, 00°55’N 29°20.7’W, Brazil; female, 5.4 mm, same data as male. Scale bars: 1 mm for mHb; 0.5mm for fHb.

FIGURE 2. Pleonexes lowryi sp. nov. Holotype, male, 6.0 mm, MOUFPE 15519; paratype, female, 4.8 mm, MOUFPE 15520. Scale bars: 0.5 mm for A1–2, 0.3 mm for Hd, 0.1 mm for the remaining.

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.

FIGURE 4. Pleonexes lowryi sp. nov. male, 5.8 mm, São Pedro and São Paulo Archipelago, 00°55’N 29°20.7’W, Brazil. Scale bar: 0.2 mm.

FIGURE 5. Pleonexes lowryi sp. nov. Holotype, male, 6 mm, São Pedro and São Paulo Archipelago, 00°55’N 29°20.7’W, Brazil, MOUFPE 15519. Scale bars: 0.5 mm.

FIGURE 6. Pleonexes lowryi sp. nov. Holotype, male, 6 mm, São Pedro and São Paulo Archipelago, 00°55’N 29°20.7’W, Brazil, MOUFPE 15519. Scale bars: 0.1 mm for U3; 0.05 mm for T; 0.2 mm for the remaining.

FIGURE 7. Pleonexes lowryi sp. nov. Male 5.8 mm, São Pedro and São Paulo Archipelago, 00°55’N 29°20.7’W, Brazil. Scale bars: 0.1 mm for US1–3; 0.02 mm for T.