Rhachotropis delicata, 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 : 29-34

Rhachotropis delicata sp. nov.

( Figs 5–8 )

Material examined. Holotype: NIWA 60481, ovigarous female, 10.3 mm. Type locality: TAN0705/285, 43°47.48´S, 175°18.56´E, Brenke sled, 27 April 2007, 420 m, Chatham Rise, New Zealand. Paratype: NIWA 60482, female 8.2 mm, same locality as holotype.

Etymology. Rhachotropis delicata sp. nov. is named for its delicate, elegant body shape.

Diagnosis. Body delicate. Rostrum longer than head. 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, pleonite 1 and 2 additionally bearing dorsolateral processes. Pereonite 3 indented. Urosomite 1 dorsolaterally smooth or bearing small dorsal hook. Telson cleft one-tenth, triangular, long and narrow.

Description. Antenna 1 shorter than antenna 2. Antenna 1 peduncle with several plumose setae; article 2 slightly longer than article 1, twice as long as article 3; flagellum 11-articulate. Antenna 2 peduncle articles 3 and 4 subequal in length, several plumose setae; flagellum 9-articulate.

Mandible with incisor process well developed, lacinia mobilis denticulate, molar process conical; palp article 1 short, less than a third of article 2; article 3 longer than 2; articles 2 and 3 with long slender setae. Maxilla 1 inner plate bearing 1 subterminal setae; outer plate with 9 denticulate spines; article 2 of palp with several slender setae, especially at tip. 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 outer plate nearly twice as long as inner plate, reaching half of article 2 of maxillipedal palp; inner margins of palp, outer plate and terminal end of inner plate setose.

Gnathopod 1 coxa 1 expanded anteriorly, rounded, coxa 2–4 subquadrate. Gnathopods similar in shape, subchelate, propodus of G1 less expanded than propodus of G2. Gnathopod 1 slighly smaller than gnathopod 2, basis bearing several small spines at anterior side; 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.

Pereopods 3 and 4 articles long and narrow, carpus and propodus bearing slender setae. Gill at pereopod 3 nearly as long as basis; gill at pereopod 4 as long as basis, fully developed oostegite extending length of basis. Pereopod 5 basis small; gill and fully developed oostegite twice the length of basis; merus longer than carpus; prododus nearly twice as long as carpus; merus, carpus and propodus bearing short setae. Pereopod 6 basis larger than that of pereopod 5, posteriorly notched; proportion of articles as in pereopod 5. Pereopod 7 basis slightly widened, posterior margin serrate; merus posteroventral angle produced; carpus nearly twice as long as merus, propodus a third longer than carpus.

First (right side) pleopod rami with 17 and 19 articles.

Uropod 1 rami subequal in length, slightly shorter than peduncle. Uropod 2 peducle about same length as outer ramus; outer ramus a quarter shorter than inner ramus. Uropod 3 rami lanceolote, subequal in length; 2.5 times longer than peduncle. Telson cleft one-tenth, more than three times as long as wide, lobes pointed apically, one plumose seta each side basally.

Remarks. Rhachotropis delicata sp. nov. was collected at the same station in 420 m depth on the Chatham Rise, east off New Zealand as R. chathamensis sp. nov.. Rachotropis delicata sp. nov. is very similar to Rhachotropis levantis , the only species of Rhachotropis previously recorded from New Zealand waters. It differs from R. levantis amongst other characters in having a longer and further cleft telson, basis of gnathopod 2 is expanded, dactyli of gnathopod 1 and 2 are shorter than palm, rami of uropod 1 are subequal in length (see Table 1).

Telson as long as or longer than uropod 3 Telson shorter than uropod 3

Telson cleft 1/10 Telson cleft 1/3

Epimeron 3 laterally smooth Epimeron 3 with lateral ridge

Urosomite 1 laterally smooth Urosomite 1 with lateral ridge

Uropod 1 rami same length Uropod 1 outer rami shorter than inner Gnathopod 2 basis expanded Gnathopod 2 basis parallel

G1 and G2 propodus extension exceeding article G 1 and G2 propodus extension small G 1 and G2 dactylus shorter than palm G1 and G2 dactylus longer than palm Morphological variation. Rhachotropis delicata sp. nov. shows some morphological variation in the first urosome. While the holotype has a completely smooth first urosomite, a small hook can be found on the paratype.

Distribution. New Zealand, Chatham Rise, 420 m.

Figures

FIGURE 5. Rhachotropis delicata sp. nov., holotype, 10.3 mm, female, NIWA 60841: a, habitus lateral; b, erpimeral plates dorsal; c, antenna 1; d, maxilla 1; e, antenna 2. Scale bars a – c 1 mm; d, e 0.1 mm.

FIGURE 6. Rhachotropis delicata sp. nov., holotype, 10.3 mm, female, NIWA 60841: a, mandible; b, maxilla 1; c, maxilliped; d, gnathopod 1; e, pereopod 4. Scale bars a – c 0.1 mm, d, e 1 mm.

FIGURE 7. Rhachotropis delicata sp. nov., holotype, 10.3 mm, female, NIWA 60841: a, pereopod 3; b, pereopod 4; c, pereopod 7; d, pereopod 6; e, pereopod 5. Scale bars 1 mm.

FIGURE 8. Rhachotropis delicata sp. nov., holotype, 10.3 mm, female, NIWA 60841: a, pleopod 1; b, uropod 2; c, uropod 3; d, uropod 1; e, egg; f, telson. Scale bars 1 mm.