Pseudorhachotropis longipalpus sp. nov.

(Figs 2–5)

Diagnosis. The same as the genus.

Type material. Holotype male, 6.2 mm; CNCR37074, dissected. Type locality. Bay of Campeche, SW Gulf of Mexico, 20°27’58.48’’N and 94°24’48.35’’W. The material was collected from soft–bottom characterized by mud (silty–clay) sediments of terrigenous origin at 2321 m in depth, on July 08, 1965 .

Etymology. This species in named after Latin longipalpus because of the long size of mandibular palp article 1.

Description. Holotype male, 6.2 mm. Body (Fig. 2): head without eyes; rostrum short, pointed, slightly directed downward; pereonal segments smooth dorsally; pleonal segments 1–3 posterodorsal teethed; urosomal segments 1–2 large with posterodorsal processes; epimeron 3 small with three–minute teeth at posteroventral corner (Fig. 5E). Antenna 1 (Fig. 3A) slightly longer than antenna 2, peduncle article 1, 1.4 x articles 2–3 combined, peduncle article 3 embedded; accessory flagellum 5–articulate, flagellum 12–articulate, article 1 of flagellum as length as articles 2–3 combined. Antenna 2 (Fig. 3A) peduncular article 4 subequal in length to 5, flagellum 9–articulate.

Mouthparts (Fig. 3). Maxilla 1 (Fig. 3B) outer plate with nine robust distal setae; inner plate with one long robust distal seta; palp article 1 naked, article 2 with four distal robust setae, two simple outer marginal setae, another inner margin, and two facial setae. Maxilla 2 (Fig. 3C) outer plate wider than inner, with 15 distal simple setae; inner plate with three distal setae, other seven inner margin. Maxilliped (Fig. 3D) inner plate half–length outer, with three molariform distal setae, and six anterolateral simple setae; outer plate with five long, other four short inner margin setae; palp article 1 with a lateral simple seta, another distal simple seta; article 2 as long as article 3, both settled in right angle; article 2 with seven inner margin robust setae, one distal and another outer margin robust setae; article 3 with six inner margin robust setae; article 4 half–length of article 3, set of tiny setae distal inner margin. Lower lip (Fig. 3F) extended laterally, inner plate missing, mandibular lobe poorly developed, naked. Upper lip (Fig. 3E) wider than long, lower margin somewhat bilobate. Left mandible (Fig. 3G) with seven incisors; lacinia mobilis quadrate, with five teeth; molar a small protuberance with two large and another small robust setae, and four small rakers; palp article 1 as long as article 2, one distal robust seta article 2; article 3 half–length of article 2, with one distal robust seta. Right mandible (Fig. 3H) with four incisors; lacinia mobilis subcircular, distal margin finely serrated; two subdistal robust setae palp article 2; rest of mandible like left one.

Gnathopods similar than those in genus Rhachotropis . Gnathopod 1 (Fig. 4A) coxa quadrangular, slightly directed forward; basis with three setae anterior margin, and 10 setae posterior margin; ischium and merus with one seta on posterior margin; carpus posterior lobe 0.4 x long dactylus, with three distal long setae; propodus subovoidal, with three distal setae; palmar margin convex, with minute plumose setae; dactylus fixing palm. Gnathopod 2 (Fig. 4B) coxa subrectangular; basis, ischium, and merus naked; carpus posterior lobe longer than dactylus, anterior and posterior margins with 6–9 setae, two plumose setae, and another one simple short seta, all distally; propodus more subovoidal than in gnathopods 1; palmar margin slightly convex with minute simple setae, palmar angle with one long robust seta, another simple seta distally; dactylus not fixing palm; gill 0.7 x long basis.

Elongate; cleft

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As long as wide; “V" inverted shape

Pereopod 3 (Fig. 5A) coxa subrectangular; basis to propodus slender; basis with four setae anterior margin, subequal in length to merus and carpus combined; propodus as long as merus; dactylus very short, gill half– length basis. Pereopod 4 (Fig. 5B) coxa rectangular; basis to propodus slender; basis 0.9 x long merus and carpus combined, propodus with three subdistal setae posterior margin, other two distally; propodus subequal in length to merus: dactylus 0.6 x long propodus; dactylus as long as carpus; gill half–length basis. Pereopod 5 (Fig. 5C) coxa subtriangular, posteroventral corner irregular; basis 0.9 x long merus and carpus combined; basis with three setae anterior and posterior margins; carpus with three setae anterior margin, other six setae posterior margin; propodus 0.6 x long merus; dactylus missing, gill 0.3 x long basis. Pereopod 6 (Fig. 5D) coxa triangular, notched posteroventral corner; basis subequal in length to ischium and merus combined; carpus as long as propodus, with four setae anterior and posterior margins; propodus with three setae anterior and posterior margins; propodus 1.2 x long carpus; dactylus missing, gill 0.3 x long basis. Pereopod 7 (Fig. 5E) coxa ovoidal, notched ventrally; basis as long as merus, with four setae anterior margin; merus with two setae anterior margin, four setae posterior margin, and other five distally; rest of pereopod missing.

Uropod 1 (Fig. 6A) peduncle 1.2 x longer than outer ramus, one subdistal robust seta inner margin; inter–ramal robust seta, 0.2 x long outer ramus; outer ramus 1. 3 x longer than inner ramus, with three inner margin setae, another one distal robust seta; inner ramus with three inner margin setae, other two short distal setae. Uropod 2 (Fig. 6B) peduncle as long as rami, with two setae outer margin, distal peduncle outer notch; rami subequal in length; outer ramus naked; inner ramus with four inner margin setae, other three outer margin setae. Uropod 3 (Fig. 6C) peduncle 1.2 x longer than rami, distal margin notched; rami subequal in length; inner ramus flat, with three setae on each margin; inner ramus narrow, naked. Telson (Fig. 6D) as long as wide, “V” inverted shape; incised 0.3 x posterior margin, each lobe with 1–2 robust setae.

Remarks. The new genus Pseudorhachotropis is easily distinguished for the known genera of eusirid amphipods by antenna 1 with accessory flagellum 5–articulate; mandibular molar smooth conical protuberance with large robust setae; dorsal ornaments pattern, such as pereonal segments smooth, pleonal segments 1–3 with posterodorsal teeth, urosomal segments 1–2 large posterodorsal processes; coxa 1 quadrangular, unproduced anteriorly; uropod 1 interramal robust seta present; epimeron 3 with three teeth at posteroventral corner; telson as long as wide, “V” inverted shape incised 0.3 x in length to posterior margin, each lobe with 1–2 robust setae. In addition, a distinctive morphological character is the palp article 1 long, subequal in length to article 2. Specific differences among eusirids genera are summarized in Table 1.