Paranarthrura arctowskii Jóźwiak & Błażewicz-Paszkowycz, 2011, n. sp.

Paranarthrura arctowskii n. sp.

Figures 2–5, Plate 1

Material examined: Holotype: juvenile male, ZMH K- 42681, 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. Paratypes: two mancas, ZMH K- 42683, 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 and one juvenile male (dissected on slides), ZMH K- 42682 (ZMH K- 42694 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; one female, ZMH K- 42684, ANTXXII/3, PS67/154-9-S, 62° 31.47'– 62° 31.36' S, 64° 39.45'– 64° 39.25' W, depth 3804–3808 m, 30 Mar 2005; one female and one juvenile male, ZMH K- 42685, ANTXXII/3, PS67/154-9-E, 62° 31.47'– 62° 31.36' S, 64° 39.45'– 64° 39.25' W, depth 3804–3808 m, 30 Mar 2005; one male, six females, 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; eight females, one manca, 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; three females, BIO 4-EBS-3A, 74º 39.731'– 74º 40.109' S, 104º 63.746'– 104º 62.019' W, depth 489–527 m, 0 7 Mar 2008; one male (partially dissected on slide), ZMH K- 42695, ST-EBS-2, 59° 30.42'– 59° 30.40' S, 27° 18.15'– 27° 18.47' W, depth 1019–1038 m, 28 Mar 2006; one manca, SR-EBS-6, 53° 15.19'– 53° 15.19' S, 42° 8.63'– 42° 8.89' W, depth 1016–1027 m, 12 Apr 2006; one female, USAP, Islas Orcada cruise 575, sta. 60, 56° 53.5' S, 26° 54.8' W, depth 1532–1590 m, 29 May 1975.

Paranarthrura cf. arctowskii: one female, R/V Eltanin 38, sta. 9/20, 57° 21.56' S, 149° 36.92' E, depth 3299 m; one male, R/V Eltanin 38, sta. 11/29, 49° 45.57' S, 152° 36.18' E, depth 4304 m, 28 Apr 1969; one female, R/V Eltanin 38, sta. 11/30, 49° 45.57' S, 152° 36.18' E, depth 4304 m, 28 Apr 1969; two females, sta. 9/21, 57° 21.56' S, 149° 36.92' E, depth 3299 m, 19 Apr 1969.

Diagnosis: Cephalothorax almost rounded, 15% of total body length; pleon short, 20% of total body length; chela with chitinized ventral keel fused with terminal spine; pereonites wider than long or (pereonites 3–5) as long as wide; maxillule with eight spiniform setae terminally; maxilliped endite terminal margin with pair of setae and lacking tubercles; ischium of pereopods 4–6 with one seta; uropod endopod two-articled; uropod basis projection long, exceeding length of proximal endopod article.

Etymology: This species is named in honour of Henryk Arctowski, the Polish explorer of Antarctica.

Description of juvenile male. Body (Figs 3 A, B) 2 mm long, 7.5 times as long as wide.

Carapace 15% of total body length, almost as wide as long, rounded in dorsal view.

Pereonites with hypospheniae. Pereonites 2 to 5 rounded laterally; pereonites 1 and 6 trapezoidal. Pereonite 1 as long as pereonite 6; pereonite 2 1.2 times as long as pereonite 1; pereonite 3 little longer than pereonite 2; pereonites 4 and 5 subequal to pereonite 3. Pleon 20% of total body length; pleonites equal; pleotelson as long as combined length of last three pleonites, with pair of simple setae distally and pair of setae on apex.

Antennule (Fig. 4 A): almost 1.4 times as long as carapace, 4-articled, relatively slender (10 times as long as wide); article 1 about as long as combined length of remaining articles, with one bipinnate seta in middle and two bipinnate setae distally on outer margin; article 2 0.3 times as long as article 1, with one simple and two bipinnate setae distally on outer margin; article 3 0.6 times as long as article 2, with two setae distally; article 4 2.6 times as long as article 3, with one bipinnate and four simple setae terminally.

Antenna (Fig. 4 B): 6-articled; article 2 short, with one simple and one minute seta subdistally; article 3 0.7 times as long as article 2, with one seta distally on outer margin; article 4 four times as long as article 3, with one bipinnate seta in middle and three bipinnate setae distally; article 5 0.4 times as long as article 4, naked; article 6 0.3 times as long as article 4, with one seta subdistally and two setae terminally.

Mouthparts: labrum (Fig. 4 D) hood-shaped, covered by numerous minute setae. Mandibles (Figs 4 E, F) molar not discovered (possibly grossly reduced), mandible incisor crenulated, well calcified, lacinia mobilis in left mandible as thick spine. Maxillule (Fig. 4 G) with eight spiniform setae terminally (one serrated) and one simple seta distally on outer margin; palp (Fig. 4 G') with two terminal setae. Maxilla not recovered. Labium (Fig. 4 H) lobes rounded with dense setation distally. Epignath (Fig. 4 I) slender, naked, pointed distally. Maxilliped (Fig. 4 J) bases slender, elongate and fused, without distal setae; endites with two simple setae on distal margin; distal tubercles not observed. Palp article1 naked; article 2 with two short and one long setae on inner margin; article 3 with two simple setae on inner margin and one seta distally; last article with one simple and four serrated setae terminally.

Cheliped (Fig. 5 A; Plate 1): sclerite posterior to basis unfused ventromedially (Figs 3 C, C’); basis wider than long, with one short seta dorsally; merus triangular, with one seta ventrally; carpus almost twice as long as wide, with one seta dorsally, one distodorsally and two setae ventrally; propodus 1.3 times as long as wide, with one long and two short spines on inner surface of chela; fixed finger as long as combined length of dactylus and unguis, with strongly calcified ventral keel, one ventral seta and three setae on inner margin; dactylus with one tooth on inner margin.

Pereopod 1 (Fig. 5 B): coxa with simple seta; basis 4.5 times as long as wide, naked; ischium with simple seta; merus almost as long as carpus, with one serrated seta distoventrally; carpus with one serrated seta distodorsally and with one serrated seta and one spiniform seta distoventrally; propodus 1.5 times as long as carpus, with two serrated setae distoventrally, ventral margin with minute spines. Dactylus about 0.8 times as long as unguis, both together 0.75 times as long as propodus.

Pereopod 2 (Fig. 5 C): similar to pereopod 1, but basis with bipinnate seta dorsally and propodus only with one serrated seta distoventrally.

Pereopod 3 (Fig. 5 D): similar to pereopod 2.

Pereopod 4 (Fig. 5 E): basis 4.2 times as long as wide, with one bipinnate seta ventrally; ischium with one simple seta; merus 0.3 times as long as basis, with two serrated setae distoventrally; carpus about 1.4 as long as merus, with one bipinnate seta distodorsally, one serrated seta distally and two serrated setae distoventrally; propodus subequal carpus, with two serrated setae distoventrally and with one serrated seta and one spine distally, ventral margin with minute spines. Dactylus as long as propodus; unguis 0.75 times as long as dactylus.

Pereopod 5 (Fig. 5 F): similar to pereopod 4, but basis with one bipinnate seta on dorsal margin.

Pereopod 6 (Fig. 5 G): similar to pereopod 5, but propodus with two spiniform and two serrated setae.

Pleopod (Fig. 5 H): basal article about as long as wide, with short seta; both rami gently rounded, naked; exopod 0.8 times as long as endopod.

Uropod (Fig. 5 J): basal article as long as wide, naked; basal projection with one short and one long setae terminally; endopod article 1 0.75 times as long as basal projection, naked; article 2 with one long seta subdistally and one simple and one bipinnate seta terminally.

Mature female: similar to juvenile male, but lacking pleopods.

Mature male: similar to juvenile but with fully-developed pleopods (Fig. 5 I), of which rami are equal in length; exopod with one subdistal seta and six setae terminally; endopod with nine setae terminally. Antennule (Fig. 4 C) stouter than in juveniles, with article 1 about 3.5 times as long as wide, with two bipinnate setae distally, article 2 almost 0.4 times as long as article 1, with two simple and two bipinnate setae distally, article 3 square, with two distal, simple setae, terminal article 2.4 times as long as article 3, with five simple and two bipinnate setae distally and subdistally.

Distribution: The s pecies is known from north-west Cape Norway, the vicinity of Pine Island Bay (Amundsen Sea), west of Antarctic Peninsula, west of Macquire Island and from the Scotia Sea in the depth range 489–4304 m (Fig. 2).

Remarks: Paranarthrura arctowskii n. sp. is distinguished by the unique structure on the ventral margin of chela: the strongly chitinized terminal spine on the fixed finger continues backward and produces a keel that is bent and extends horizontally from the main axis of the chela. In addition, the dactylus of the chela is comparatively slender (4.5 times as long as wide) while the carapace is clearly rounded in dorsal view.

PLATE 1. Paranarthura arctowskii n. sp. details of chela.