Bythocypris polarsterni Brandão, 2008, sp. nov.

Bythocypris polarsterni sp. nov.

(Figs. 24.N, O, R, S, V, W, 33–35, 36.A–D)

Etymology. From the RV Polarstern.

Material: 4 live specimens. Holotype: 1 A F (SNB 0137), ANDEEP II, # 134–4–E, ZMH K­ 41314. Paratypes: 1 (A­1) (SNB 0246), 2 (A­?2) (SNB 0 383, B 0384), ANDEEP II, # 134–4–S, ZMH K­ 41315.

Distribution. NW Weddell Sea, Southern Ocean (Atlantic Sector), 4059.4 to 4068.7m.

Measurements (Fig. 34). Holotype, LV, L 2.23mm, H 1.07mm; RV, L 2.22mm, H 1.01mm. Paratypes, LV, (A­1) L 1.76mm, H 0.88mm; (A­2) L 1.37–1.41mm, H 0.68mm.

Diagnosis. Valves large; lateral outline quite rectilinear, subtrapezoidal; inequilateral, both anterior and posterior margins narrowly rounded, but anterior broader than posterior; ventral margin straight in LV and fairly straight in RV. Podomere VI of AII with 1 long articulated claw, 1 short fused (!) claw, and 1 or 2 short thin setae. Vibratory plate of MxI with 4 or 5 strahlen and 21 or 22 feathered setae. Vibratory plate of ApV with 4 strahlen plus around 8 setae. Fu with 3 small, 1 long, and 3 medium sized setae. Genital lobe sub­hemispherical with double coiled internal tube.

Description. Valves large; lateral outline of both valves rectilinear, subtrapezoidal; inequilateral, both anterior and posterior margins narrowly rounded, but anterior broader than posterior; dorsal margin broadly rounded, posterodorsal and anterodorsal margins straight, but without conspicuous angles; ventral margin straight in LV and fairly straight in RV. Adductor muscle scars subdivided but bythocypridid in aspect, occupying a very small area (less than 1/7 of valve height). Calcified inner lamella broad. Zone of concrescence very narrow, marginal pore canals straight and short. Radial pore canals simple, with wide rim.

Appendages strongly pigmented, dark brown, conspicuous even through closed valves. AI with slender thin podomeres I–II; very short podomeres IV–VII; chaetotaxy 1(0/0), 2(0/0), 3(.2/0), 4(.1/.1), 5(.2/.2), 6(.3/.2), 7(0/0:3­4). Exopodite of AII with 2 long and 1 short setae; podomere VI with 1 long, articulated claw, 1 short fused (!) claw, and 1 or 2 short thin setae; chaetotaxy 1(0/0: 2i), 2(.1/0: 1i), 3(0/.2­3.1,1), 4(0/.2­3r.1,1), 5(.1.2./.1.1c), 6(0/0:1c,1­2,1fc). Base of Md with 1 dorsal seta, 1 or 2 bifurcate teeth, and 3 to 4 trifurcate teeth; palp podomere III elongated; chaetotaxy 1(0/0: 1i), 2(.2/.1: 1i), 3(.3./.1: 2i), 4(.1/0:2c,2). Vibratory plate of Mx I with 4 or 5 strahlen and around 21 feathered setae. Vibratory plate of ApV with 4 strahlen and around 10 feathered setae; chaetotaxy (.1.2.3/0), 2(0/.2), 3(0/.1), 4(0/.1), 5(0/0:1c,1). ApVI and ApVII with 1 tiny seta on expodite; 1(.1.1.2/0), 2(0/.2), 3(0/0), 4(0/.1), 5(0/0:1c,1). Fu with 3 short proximal setae, 1 long seta, and 3 medium­sized distal setae. One long seta between Fu rods. Genital lobe subhemispherical, with double coiled internal tube.

FIGURE 33. Occurrence of Bythocypris polarsterni sp. nov, Bythocypris sp. aff. B. polarsterni sp. nov. and B. elongata informal species group (published information). Legend: — type locality of B. elongata Brady (1880) and Puri and Hulings (1976); — Chapman (1910); "—Le Roy (1943); — Key (1954); — Maddocks (1969); — B. polarsterni sp. nov. (herein); Π— Bythocypris sp. aff. B. polarsterni sp. nov. (herein).

Remarks. Like Bythocypris malyutinae sp. nov. (see above), Bythocypris polarsterni sp. nov. present several bythocypridid characters: (1) carapace (subtriangular, thin and smooth), (2) antenna I with not very long setae; (3) genital lobe with short internal tube; (4) adductor muscle scars arranged in three anterior and one posterodorsal rows. Otherwise, the antenna II in B. polarsterni sp. nov. presents the bairdiid claw fused to podomere VI. Similarly, the female genitalia and the furcae of B. polarsterni sp. nov. are very similar to that of Zabythocypris helicina Maddocks, 1969. Otherwise, the valves of B. polarsterni sp. nov. are typical of the genus Bythocypris.

Bythocypris polarsterni sp. nov. is similar to B. elongata, but the former differs in being higher in relation to length, with a more smoothly rounded dorsal margin, and straighter ventral margin, and in presenting subdivided adductor muscle scars. The lateral outline of the valves of the new species described herein differs from: (1) B. reniformis, B. affinis, B. prolata, B. praerenis sp. nov. and B. richarddinglei sp. nov in being more subtriangular; (2) B. mozambiquensis, B. promoza, B. eltanina, B. spiriscutica and B. malyutinae sp. nov. in being more elongated, and rectilinear.