Rhachotropis abyssalis Lörz, 2010, sp. nov.
Creators: name: Lörz, Anne-Nina
Publisher: name: Zenodo
Year: 2010
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Amphipoda
Eusiridae
Rhachotropis
Rhachotropis abyssalis

description: Rhachotropis abyssalis sp. nov.
(Figs 13–17)
Material examined. Holotype: NIWA 60483, male, 13.2 mm, TAN0802/ 288, Brenke sled, 66°45.28’S, 171°9.7’E, 12 March 2008, depth 3379–3380 m, Admiralty seamount, Ross Sea, Antarctica.
Paratypes: NIWA 60484, female, 13.2 mm, photographed on board immediately after sampling (Fig 17); damaged female, 15.5 mm; damaged male, 13.4 mm; all paratypes same collection data as holotype.
Etymology. Rhachotropis abyssalis sp. nov. is named for the abyssal habitat in the northern Ross Sea from which the species was collected.
Diagnosis. Body delicate. Rostrum longer than head. Antenna as long as body. Eyes absent. Head twice as long as pereonite 1, lateral lobes strongly produced. Pereonites smooth. Pereopod 7 longer than body. All pleonites bearing dorsal processes. Pereonite 3 indented. Urosomite 1 bearing dorsal process, urosomites 2 and 3 smooth. Telson cleft, long and narrow.
Description. Antenna 1 and 2 equal in length. Antenna 1 article 2 of peduncle with several plumose setae, article 2 slightly shorter than first article, twice as long as third article; flagellum 67 articles, the first 22 articles very short and bearing many setae. Antenna 2 peduncle article 4 shorter and wider than article 5, with several plumose setae, flagellum of 65 articles.
Mandible with incisor process well developed, lacinia mobilis denticulate, molar process conical; palp article 1 short, about one fifth of article 2; article 3 longer than 2; articles 2 and 3 with long slender setae. Maxilla 1 inner plate bearing 1 subterminal plumose seta; outer plate with 9 denticulate spines; article 2 of palp with several slender setae at tip; palp twice as long as outer plate. Maxilla 2 inner and outer plate subequal in length; margins bearing stout and slender setae; inner plate wider than outer plate with 1 plumose seta. Maxilliped palp more than twice length of outer plate; article 2 of palp with epibionts. Maxilliped outer plate twice as long as inner plate, not reaching half of article 2 of maxillipedal palp; inner margins of palp, outer plate and terminal end of inner plate setose, a plumose setae on article 2 of maxillipedal palp. Labrum entire, with setae at broadly rounded terminal corners. Hypopharynx outer lobe setose, inner lobes broken off.
Gnathopod 1 coxa 1 produced, reaching longer than head, coxa 2–4 subquadrate. Gnathopods similar in shape, subchelate. Gnathopod 1 slighly smaller than gnathopod 2, basis bearing small spines at anterior side; merus long setae at posteroventral corner; carpus lobe extending width of propodus, spines at terminal end of lobe; propodus widened, oval; dactylus slender, nearly reaching end of palm. Gnathopod 2 basis bearing small spines at anterior side; ischium with pointed protrusion at posterior margin; merus with long setae at posteroventral corner; carpus lobe extending width of propodus, spines at terminal end of lobe; propodus widened, oval; dactylus slender, reaching end of palm.
Pereopods 3 and 4 basis long and narrow with few setae, carpus–dactylus broken off. Gill at pereopod 4 as long as basis. Pereopod 5 basis posterior margin serrate; merus bearing short setae; carpus–dactylus broken off. Pereopod 6 basis larger than that of pereopod 5, slightly serrate. Pereopod 7 basis parallel, merus long, slender, carpus–dactylus broken off.
Pleopod 1 rami with 32 articles, peduncle two-thirds rami length.
Uropod 1 outer ramus slightly shorter than inner ramus; rami about one quarter shorter than peduncle; rami and peduncle serrate. Uropod 2 peducle shorter than outer ramus; outer ramus shorter than inner ramus; peduncle and outer ramus slightly serrate. Uropod 3 and telson lost. The telson of the male and female paratypes differ in width to length relation as well as percentage cleft. Telson cleft to at least one-tenth, longer than wide.
Remarks. The live specimens of R. abyssalis sp. nov. are very translucent, as shown on the photographs of a paratype (NIWA 60484), taken shortly after being caught (Fig 17).
The dorsal features of R. abyssalis sp. nov. are very similar to R. distincta (Holmes, 1908). The new species can be distinguished from R. distincta by its produced first coxa and serrate basis of pereopod 7.
Not common amongst Rhachotropis species is the nearly parallel (not widened) basis of pereopod 7, seen in R. distincta and R. abyssalis sp. nov.
Epibionts. Epibionts were found on the maxilliped, 2 on the left and a further 2 on the right maxillipedal palp.
Molecular data. COI sequences were obtained from the holotype of R. abyssalis sp. nov. (NIWA 60483; BOLD Accession No: AMPNZ0 9509) and one paratype (NIWA 60484; BOLD Accession No: AMPNZ09409).
Morphological variation. The dorsolateral protrusions of epimeral plates 1 and 2 are less obvious in the holotype (Fig 13 A) than in the paratype (NIWA 60484) (Fig 17).
Sexual dimorphism of the antenna and telson was observed. Male specimens have more than 20 additional short flagellar articles on antenna 1 and these bear many setae. The telson of the males is more cleft and the apical tips of the narrower female telson are wider apart.
Distribution. Ross Sea, Antarctica, close to Admiralty seamount; 3380 m.
description: Published as part of 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, pp. 22-48 in Zootaxa 2482 on pages 39-45, DOI: 10.5281/zenodo.195450