Bythocypris weddellensis Brandão, 2008, sp. nov.

Bythocypris weddellensis sp. nov.

(Figs. 18, 39–42)

Etymology. In reference to its occurrence in the Weddell Sea.

Material. 3 A. Holotype: 1 A M (SNB 0191), ANDEEP III # 142–5–E, ZMH K­ 41325. Paratypes: 1 A M (SNB 0398), ANDEEP II, # 136–4–E, ZMH K­ 41327. 1 A F (SNB 0251), ANDEEP III # 80–9–E, ZMH K­ 41326.

Distribution. Weddell Sea, Southern Ocean (Atlantic Sector), 3102 to 4782m.

Measurements (Fig. 18). Holotype, LV, L 1.04mm, H 0.52mm; RV, L 1.04mm, H 0.50mm. Paratypes, LV, A M L 1.07mm, H 0.53mm; AF, L 1.22mm, H 0.63mm.

Diagnosis. Valves small, smooth, glossy, oval/sub­rectangular in lateral view. Podomere VI of AII with 1 large claw, 2 medium­sized setae, and 1 short seta. Vibratory plate of MxI with 7 strahlen and around 25 feathered setae. Vibratory plate of ApV with 4 or 5 strahlen and around 10 feathered setae; podomere V with 1 large claw and 2 short setae. Fu with 5 tiny proximal setae and 3 medium­sized distal setae. Hemipenis with sub­hemispherical basal capsule; with a tubular, short and thick distal process, copulatory tube short and curved. Genital lobe sub­oval with a distal, strongly sclerotized, beak­shaped process.

Description. Valves small, smooth, glossy, oval/sub­rectangular in lateral view. Larger valve with rounded outline; smaller valve with slightly angulated outline; posterior margin obtuse, and less broadly rounded than anterior margin; dorsal margin slightly arched; faint or no ventral indentation; fused marginal zone narrow, with numerous straight marginal pore canals; vestibules constricted. Carapace compressed laterally. Adductor muscle scars composed of 3 anterior scars plus one posterodorsal scar. Single female valves considerably larger than both males. In the holotype RV is larger than LV, in both paratypes LV is larger than RV.

Labrum and hypostome bairdioid in structure (not elongated). AI robust, with not very long setae; chaetotaxy 1(0/0), 2(1/0), 3(2/0), 4(0/0­1), 5(2/2), 6(3/2), 7(0/0:5). AII robust, with short and thick podomeres; exopodite with 2 long and 1 short setae; podomere VI with 1 large claw, 1 short seta and 2 medium­sized setae, all of them flexibly articulated to podomere distal margin; chaetotaxy 1(0/0:2), 2(0/0: 2i), 3(0/.3.2), 4(.2r/1,1r), 5(.1/.2), 6(0/0:1,1c,2). Masticatory process of Md with 2 bifid plus 3 trifid teeth and several setae; exopodite with 3 long feathered setae; chaetotaxy of palp 1(0­1/.1: 1i), 2(.2/.1: 1i), 3(.6/1:2e), 4(.2/0:3­4,1c). Vibratory plate of MxI with 7 strahlen and around 25 feathered setae; endites with several broad claws and simple setae; ventral endite with 2 ventral setae; other 2 endites with 1 ventral seta each; palp with 4 dorsal simple setae, 2 ventral simple setae, and 1 distal robust finely feathered claw. Vibratory plate of ApV with 4 or 5 strahlen and around 10 feathered setae; chaetotaxy 1(1.1.2/0: 2i), 2(.2/0), 3(.1/0), 4(.1/0), 5(0/0:1r,1c,1). ApVI with 1 or 2 setae on exopodite, chaetotaxy 1(.1.1.1­2/0), 2(.1­2/0), 30/0), 4(.1/0), 5(0/0:1r,1c,1). ApVI 2 setae on exopodite, chaetotaxy 1(.1.1.2/0), 2(.2/0), 3(0­1/0), 4(.1/0), 5(0/0:1r,1c,1). Fu with 5 tiny ventral setae and 3 medium­sized feathered distal setae; 1 tiny seta between Fu rods. Brush­shaped organ symmetrical, with short rods and numerous very long setae. Hemipenis with sub­hemispherical basal capsule, plus tubular, thick distal process, and curved copulatory process attached near a sub­circular, rugose process. Genital lobe rounded, with distally strongly sclerotized, beak­shaped process, and a short, coiled, thick, internal tube.

Remarks. Bythocypris weddellensis sp. nov. resembles the genus Anchistrocheles in the valve morphology (very delicate, with sub­rectangular outline, narrow zone of concrescence and restricted vestibule), and the genus Bythocypris in soft part morphology (labrum and hypostome “normal” bairdioid, not prolonged anteroventrally in flexible jawlike snout; podomere 6 of AII with long distal claw and 3 smaller setae; distal claws of AII and appendages V to VII not terminated by right angled, bevelled hook; Md and MxI also “normal” bairdioid, not elongated; maxillar vibratory plate with 7 strahlen; furca with 3 long and 5 very short setae). Since the carapace of bairdioids appear to show more evolutionary plasticity than the soft parts, and other species of the genus Bythocypris also present small, sub­rectangular carapaces, Bythocypris weddellensis sp. nov. is herein assigned to the genus Bythocypris.

Bythocypris weddellensis sp. nov. is very similar to Anchistrocheles antemacella Maddocks, 1969, which was described from 62 subfossil specimens collected in the Mozambique Channel (1280 to 2750 m); but Bythocypris weddellensis presents the following characters: (1) more rounded outline, instead of sub­rectangular; (2) anterodorsal margin straight, instead of curved; (3) more acute and elevated posterior margin; (4) dorsal margin arcuate, instead of straight and subparallel to ventral margin.

Anchistrocheles hartmanni Maddocks, 1976 is similar in valve outline to B. weddellensis, but the former species presents the following differences in the soft parts: (1) hemipenis and genital lobe outline, (2) fused podomere VI and VII of AI; (3) fused podomere IV and V of ApV; (4) Fu with just 3 setae. Anchistrocheles mcquadei Maddocks, 1976 and A. angulata (Brady, 1870) has a very distinct hemipenis and more elongated Md and MxI.

The valves of Bythocypris weddellensis sp. nov. differ from Bythocypris reniformis Brady, 1880 sensu Puri and Hulings (1976: Pl. 2.7–10, Fig. 1) because the former species presents a more rounded outline, greater height in relation to length, and larger size (LV L: 1.21 to 1.27mm, instead of 1.09mm). The valves of Bythocypris [sic] reniformis recorded by Maddocks (1969, Fig. 45.J–M) from the south­western Atlantic (Albatross, #2763, 24°17’S, 42°48’30’’W, 1227m) are larger (LV L: 1.52–1.61mm), and more subtriangular than those of the new species described herein, with the maximum height of LV and RV at mid­length, instead of posterior to it. Bythocypris [sic] reniformis recorded by Maddocks (1969, Fig. 45.N–U) from the Mozambique Channel, south­western Indian Ocean (RV Anton Bruun, cruises 7 and 8, #365D, 23°20’S, 43°33E, 695– 475m) present more similar, rectilinear outline to B. weddellensis sp. nov., but a more arcuate LV dorsal margin, and more rounded RV dorsal margin.

B. eltanina Maddocks, 1969, B. spiriscutica Maddocks, 1969, B. promoza Maddocks, 1973, Bythocypris elongata Brady, 1880, Bythocypris mozambiquensis Maddocks, 1969, and Bythocypris prolata Maddocks, 1969 are more subtriangular than B. weddelensis sp. nov. Additionally, B. affins affins Brady, 1886 (sensu Brady & Norman 1889: 242), Bythocypris affins madagascarensis Maddocks, 1969, and Bythocypris richarddinglei sp. nov. are more subquadrate and less elongate than B. weddellensis sp. nov.