Rhachotropis rossi, Lörz, Anne-Nina, 2010

Lörz, Anne-Nina, 2010, Deep-sea Rhachotropis (Crustacea: Amphipoda: Eusiridae) from New Zealand and the Ross Sea with key to the Pacific, Indian Ocean and Antarctic species, Zootaxa 2482, pp. 22-48 : 34-39

Rhachotropis rossi sp. nov.

( Figs 9–12 )

Material examined. Holotype: NIWA 45813, ovigarous female, 11.8 mm, TAN0802/188, Brenke sled, 68°33.7’S, 178°22.19’W, 1 March 2008, 3210 m, Scott Island, Ross Sea, Antarctica .

Etymology. Rhachotropis rossi sp. nov. is named after James Ross, the discoverer of the Ross Sea, where the species was collected.

Diagnosis. Body delicate. Rostrum shorter than head. Eyes absent. Head twice as long as pereonite 1, lateral lobes strongly produced. Pereonites smooth. All pleonites bearing small dorsal processes, pleonite 1 and 2 additionally bearing very small dorsolateral processes. Pereonite 3 indented. Pereonite 3 and urosomite 1 with dorsal ridge. Urosomites 1–3 dorsolaterally smooth. Telson slightly cleft, triangular, long and narrow.

Description of holotype. Antenna 1 broken off, with more than 10 articles.

Antenna 2 article 3 of peduncle shorter than article 4, with several plumose setae; flagellum 18-articulate.

Mandible with incisor process well developed, lacinia mobilis denticulate, molar process conical; palp article 1 short, less than a third length of article 2; article 3 longer than 2; articles 2 and 3 with long slender setae; 2 plumose setae at tip of palp. Article 2 of maxillipedal palp bearing epibiont. Maxilla 1 inner plate bearing 2 subterminal plumose setae; outer plate with 9 denticulate spines; article 2 of palp with several slender setae, especially at tip and with epibionts. Maxilla 2 inner and outer plate subequal in length; margins bearing stout and slender setae; inner plate wider than outer plate with several small plumose setae. Maxilliped outer plate nearly twice as long as inner plate, reaching half of second article of maxillipedal palp; inner margins of palp, outer plate and terminal end of inner plate setose. Inner plate, outer plate and maxillipedal palp bearing total of nine epibionts. Hypopharynx inner and outer lobe with terminal setae, outer lobe separated by wide gap.

Coxa 1 produced, coxa 2–4 subquadrate. Gnathopods similar in shape, subchelate. Gnathopod 1 slighly smaller than gnathopod 2; basis with ridge along its length; basis, merus, ischium long setae at posteroventral corner; carpus long setae terminal end of lobe; propodus widened, oval; dactylus slender, not reaching end of palm. Gnathopod 1 gill half length of basis. Gnathopod 2 basis with ridge along its length; ischium with long setae at posteroventral corner; carpus with long setae at terminal end of lobe; propodus widened, oval; dactylus slender, not reaching end of palm. Oostegite of gnathopod 2 extending beyond basis.

Pereopods 3 and 4 carpus and propodus long and narrow, all articles except dactylus bearing slender setae. Oostegites of pereopod 3 and 4 much longer than basis. Gill at pereopod 4 longer than basis. Pereopod 5 basis small; basis and merus bearing short setae; carpus–dactylus broken off. Pereopod 6 basis larger than that of pereopod 5; proportion of articles as in pereopod 5, but also carpus–dactylus missing. Pereopod 7 missing.

Pleopod 2 rami with 21 and 26 articles.

Uropod 1 rami subequal length, shorter than peduncle. Uropod 2 peducle shorter than inner ramus; outer ramus a quarter shorter than inner ramus. Uropod 3 rami lanceolote, subequal in length; longer than peduncle. Telson slightly cleft, to less than one-tenth of its length, more than three times as long as wide.

Remarks. R. rossi is rather similar to R. multesimus , but can be distinguished by a longer rostrum, a produced, pointed coxa 1 and a telson that is cleft for less than a tenth versus about one third of the telson length.

Epibionts. Epibionts were found on the mandibular palp, on the maxillar palp and the maxilliped.

Molecular data. COI sequences were obtained from the holotype of R. rossi NIWA 45813 (BOLD Accession No: ANZR47008).

Distribution. South of Scott Island, Ross Sea, Antarctica , 3210 m.

Figures

FIGURE 9. Rhachotropis rossi sp. nov., holotype, 11.8 mm, female, NIWA 45813: a, habitus lateral; b, habitus dorsal; c, maxilliped; d, hypopharynx; e, Antenna 2. Scale bars a, b, e 1 mm; c, d 0.1 mm

FIGURE 10. Rhachotropis rossi sp. nov., holotype, 11.8 mm, female, NIWA 45813: a, maxilla 2; b, maxilla 1; c, mandibular palp; d, mandible; e, gnathopod 1; f, gnathopod 2. Scale bars a – d 0.1 mm, e, f 1 mm.

FIGURE 11. Rhachotropis rossi sp. nov., holotype, 11.8 mm, female, NIWA 45813: a, pereopod 3; b, pereopod 4; c, pereopod 5; d, pereopod 6. Scale bars 1 mm.

FIGURE 12. Rhachotropis rossi sp. nov., holotype, 11.8 mm, female, NIWA 45813: a, uropod 1; b, uropod 2; c, uropod 3; d, telson; e, pleopod 2. Scale bars 1 mm.