Pleonexes nargessi, Momtazi & Maghsoudlou, 2020

Momtazi, Farzaneh & Maghsoudlou, Abdolvahab, 2020, Pleonexes Spence Bate, 1857 (Amphipoda: Ampithoidae) in the Persian Gulf and the Gulf of Oman, Zootaxa 4895 (3), pp. 431-439 : 432-438

Pleonexes nargessi sp. nov.

( Figs 1–4 )

Material examined. Holotype: male, 6.9 mm ( INIOC1–37 S) Chapahn (28°20’53”N, 51°11’00”E) . Paratypes: male, 7.2 mm and 2 females, 6.5–7.4 mm ( INIOC1–39 S), Chapahn Village (28°20’53”N, 51°11’00”E); 3 males, 6.1–7.1 mm ( INIOC1–40 S), Tiss (25˚21’21”N, 60˚36’15” E); male, 5.8 mm ( INIOC1–41 S), Qeshm Island (26°58’5”N, 56°14’53”E) .

Description. Based on holotype, male, 6.9 mm, INIOC1–37S.

Head. Head as long as deep. Antenna 1, 1.4 × length of antenna 2; peduncular article 1 longer than article 2, with distal robust setae; flagellum with 34 articles. Antenna 2, peduncle densely setose on ventral margin; article 4 subequal to article 5; flagellum with 8 articles, 0.65 × length of peduncular article 5. Upper lip distally setose. Lower lip, outer plates notched forming a deep distal cleft. Mandible molar well developed, triturating, accessory setal row with 4 serrate setae; palp 3-articulate, article 1 shorter than article 2; article 2 longer than article 3, with 7 marginal palmate setae; article 3 with 9 terminal palmate setae. Maxilla 1 (based on paratype, INIOC1-41S) inner plate with 3 setae; palp article 2 with 6 robust setae. Maxilla 2, inner plate narrower than outer plate. Maxilliped, outer plate with row of large robust setae along medial margin, palp 4-articulate.

Pereon. Gnathopod 1 sexually dimorphic; smaller than gnathopod 2; coxa 1 subequal to coxa 2, anteriorly produced, anteroventral corner rounded; basis anterodistal lobe large, rounded, with 4 robust setae; ischium small, trapezoid-shaped; merus anterodistal lobe acute; carpus shorter than propodus, subtriangular, with 2 robust setae on anterior margin; propodus subrectangular, length 1.5 × width, palm acute, with a defining large robust seta on proximal tooth; dactylus subequal in length to palm, inner margin crenate. Gnathopod 2 sexually dimorphic; coxa slightly longer than width; basis with large anterodistal lobe, with 6 robust setae; carpus shorter than propodus, subtriangular, with small posterodistal lobe; propodus 1.9 × width, produced anterodistally, anterior margin with fringe of slender setae; palm oblique with a narrow cleft, posterior margin produced into a short, truncated, thumb-like process; dactylus short and stout. Pereopods 3–4 bases slightly expanded, merus longer than carpus; propodus with multi slender setae on posterior margin. Pereopod 5, coxa with two robust setae; basis expanded, with one robust setae on posteriodistal corner; merus longer than carpus, subrectangular; carpus subquadrate, short; propodus subrectangular, slightly expanded distally, with 2 robust setae on posterior margin and 2 distal robust setae; dactylus strongly curved. Pereopod 6 and pereopod 7 same; basis slightly expanded; ischium trapezoid; merus longer than carpus; propodus with three distal robust setae; dactylus simple.

Pleon. Uropod 1, sexually dimorphic; peduncle with 7 robust setae, with long fringe of slender setae that reach to end of peduncle, with small rounded distoventral spur; rami unequal, outer ramus subequal to peduncle with robust setae; inner ramus slightly shorter than outer ramus, with multi robust setae. Uropod 2 peduncle with 2 distolateral robust setae; rami unequal; outer ramus longer than peduncle, with multi robust setae; inner ramus shorter than outer ramus, with multi robust setae. Uropod 3 peduncle longer than broad; peduncle with 5 distal robust setae, inner ramus 2.1 × peduncle, with 2 apical and 2 marginal robust setae and 4 long simple setae; outer ramus with 2 apical large curved robust setae. Telson (based on paratype), subtriangular, apically rounded, with 2 apical and multi lateral setae.

Female (sexually dimorphic characters). Based on paratype, 7.4 mm, Chapahn (28°20’53”N 51°11’00”E). Antenna 1, 1.3 × length of antenna 2; peduncular article 1 subequal to article 2, with distal robust setae; flagellum with 21 articles. Antenna 2, peduncle densely setose on ventral margin; article 4 subequal to article 5; flagellum with 17 articles. Gnathopod 1, subequal to gnathopod 2; carpus anterior margin without robust seta. Gnathopod 2, palm sinusodial, with 1 robust seta defining palm. Uropod 1 peduncle with 12 lateral robust setae, with long fringe of slender setae, without small rounded distoventral spur.

Etymology. The name nargessi is derived from the first author’s mother’s name. A supportive mother in the Middle East, that despite of having no chance for higher education, always encouraged her daughter to progress in science.

Variations. The length of tooth on the palm of male gnathopod 2 depends on the body length. In most juveniles (INIOC1–41S), the tooth on the palm of gnathopod 2 does not reach the middle of palm ( Fig. 3 ).

Remarks. Pleonexes nargessi sp. nov. is most similar to P. kava ( Myers, 1985) , that was described from the Pacific Ocean ( Fiji), in having the distal round interannal spur on peduncle of first uropod, V-shape cleft on palm of second male gnathopod, and short flagellum on second male antennae. However, Pleonexes nargessi sp. nov., differs from P. kava by the following features (features of P. kava in parentheses): male gnathopod 1 with proximal angle in the palm (absent), longer third uropod, ratio of L/W is equal to1.9 (shorter, L/W is 1.4), elongated propodus in second male gnathopod, ratio of L/W is 1.8 (L/W is 1.4) and merus on third pereopod, ratio L/W is 1.4 (L/W is1), non-prehensile pereopod 6 and 7 (prehensile). It seems P. kava is a complex species. There is no homogeneity on the diagnosis characters that Myers (1985) is mentioned for describing P. kava such as short flagellum in second antenna (less than peduncle but not shorter than last article of peduncle) and telson shape. The material of A. kava from Australia [ Peart (2007) and Poor & Lowry (1997)] have flagellum shorter than last peduncle article in second antenna. In the numbered material, the shape of telson, and the palm of second male gnathopod are different from that of type specimens and other reported material. In the Australian materials against type specimen, the apical part of telson is truncated and the V-shaped excavation in the palm of second male gnathopod is not clear.

Figures

FIGURE 1. Pleonexes nargessi sp. nov., holotype, male 6.9 mm (INIOC1–37S) and female 7.4 mm (INIOC1–38S), Persian Gulf, Iran. Scale = 1 mm.

FIGURE 2. Pleonexes nargessi sp. nov., holotype, male 6.9 mm (INIOC1–37S) and female 7.4 mm (INIOC1–38S), Persian Gulf, Iran. Scale a = 1 mm and b = 0.5 mm.

FIGURE 3. Pleonexes nargessi sp. nov., holotype, male 6.9 mm (INIOC1–37S), paratype male 5.8 mm (INIOC1–41S) and female 7.4 mm (INIOC1–38S), Persian Gulf, Iran.

FIGURE 4. Pleonexes nargessi sp. nov., holotype, male 6.9 mm (INIOC1–37S), Persian Gulf, Iran. Scale a = 1 mm and b =0.5 mm.