Paranarthrura fortispina Sieg 1986

Paranarthrura fortispina Sieg, 1986

Figures 1–2

Paranarthrura fortispina Sieg, 1986: 4, 5, 8, 64–68; Bird and Holdich, 1989: 146, 153.

Material examined: one female, two males (one dissected on slides), one manca, ZMH K- 42688 (ZMH K- 42698 for dissected specimen), ANTXXII/3, PS67/074-6-E, 71º 18.35'– 71º 18.28' S, 13º 57.71'– 13º 57.31' W, depth 1030–1040 m, 20 Feb 2005; two mancas, ZMH K- 42689, ANTXXII/3, PS67/074-6-S, 71º 18.35'– 71º 18.28' S, 13º 57.71'– 13º 57.31' W, depth 1030–1040 m, 20 Feb 2005; one female, one male, BIO 4-EBS-3D, 74º 39.038'– 74º 39.535' S, 104º 76.815'– 104º 75.903' W, depth 502–507 m, 0 7 Mar 2008; two females, one male, BIO 4-EBS-3B, 74º 40.122'– 74º 40.556' S, 104º 61.957'– 104º 60.154' W, depth 495–516 m, 0 7 Mar 2008; two females, BIO-EBS- 3A, 74º 39.731'– 74º 40.109' S, 104º 63.746'– 104º 62.019' W, depth 489–527 m, 0 7 Mar 2008.

Diagnosis: labium without medial process; dactylus of chela robust (2.7 times as long as wide); pereopod 1 propodus with spiniform seta distoventrally; uropod endopod with two articles, uropod basis projection well developed and as long as first article of endopod.

Description of male. Body (Figs 1 A, B) 3.4 mm long, 8.4 times as long as wide.

Carapace 20% of total body length, 1.2 times as long as wide.

Pereonites. All pereonites, except pereonite 5, with hyposphaenium. Pereonite 1 trapezoidal, as long as pereonite 6; pereonites 2–5 equal in length, 1.2 times as long as pereonite 1. Pleon 20% of total body length; each pleonite with simple seta on lateral margin, last pleonite with pair of setae dorsally; pleotelson as long as last two pleonites, with two setae ventrally at uropod insertion, two setae on distal margin and two setae on apex.

Antennule (Fig. 1 E): 4-articled, 0.9 times as long as carapace; article 1 twice as long as article 2, with one simple and one bipinnate seta on outer margin and two bipinnate setae distally on outer margin; article 2 with one simple seta distally and one simple and three bipinnate setae distally on outer margin; article 3 half as long as article 2, with two simple setae distally; article 4 almost three times as long as article 3, with five bipinnate setae in middle and five simple (one short and four long) setae terminally.

Antenna (Fig. 1 F): 6-articled. Article 2 with one simple distal seta and few minute spines on outer margin; article 3 as long as wide, with one simple seta distally; article 4 four times as long as article 3, with one simple and four bipinnate setae distally; article 5 half as long as article 4, with one simple, distal seta; article 6 about 0.3 times as long as article 5, with one seta subdistally and three setae terminally.

Cheliped (Fig. 1 H) sclerite posterior to basis and unfused ventromedially (Fig. 1 A’); basis 0.6 times as long as wide, trapezoidal, with dorsal seta; merus triangular, with ventral seta; carpus twice as long as basis, with one dorsal seta and two setae ventrally; propodus about as long as wide, with two short setae (one proximally and one near dactylus insertion); fixed finger as long as dactylus and unguis combined, with one ventral seta and three setae on inner margin; inner margin calcified, with tooth pointed forward; dactylus thick, twice as long as wide, with two short spines on inner margin; unguis 0.25 times as long as dactylus.

Pleopod (Fig. 1 I): basal article 0.9 times as long as rami, naked; rami subequal; exopod with one seta subdistally and six setae terminally; endopod with eight terminal setae.

Mouth parts, pereopods and uropods as in female (see Sieg 1986, pages 65–67).

Sexual dimorphism. The female differs from the male by lacking pleopods (Fig. 1 D), by having pleonites narrower than the rest part of the body and by having slender antennule with different proportions in articles (Fig. 1 G).

Distribution: The species is known from two localities in the Weddell Sea: at 75°21.88'S, 29°22.00'W (type locality) and at Cape Norway in a depth range from 1030 to 1040 m (present study) as well as in the Amundsen Sea in a depth range from 489 to 527 m (present study) (Fig. 2).

Remarks: Paranarthrura fortispina is distinguished from the other members of the genus by the robust and well-calcified cheliped dactylus. Also the species has a two-articled endopod of the uropods and a relatively long uropodal projection that reaches the end of the proximal article of the endopod. There are five other described species with a similar uropod: P. bacescui Kudinova-Pasternak, 1986; P. crassa Bird & Holdich, 1989; P. insignis Hansen, 1913; P. lusitanus Bird & Holdich, 1989 and P. tenuimanus Larsen, 2005, but all of them have a relatively narrow cheliped dactylus. The other differences between those species and P. fortispina have been discussed by Bird and Holdich (1989: 146).