Macromckenziea giambonini Brandão 2010, SP. NOV.

MACROMCKENZIEA GIAMBONINI SP. NOV.

(FIGS 7, 11–13)

Etymology: In honour of Diego Giambonini for his immense support.

Material: 8 live specimens.

Holotype: 1 A F (SNB 0030) (soft parts in glass slide, valves in micropalaeontological slide), EASIZ II, # 107, ZMH K-40809.

Paratypes: 3 A F (SNB 0029, 0031, 0032) (valves in micropalaeontological slide, soft parts in glass slide) and 4 (A-1) (in alcohol 90%), EASIZ II, # 107, ZMH K-40810.

Distribution (Fig. 7): Recent. Eastern Weddell Sea, SO, 924- 934 m.

Measurements (Fig. 7): Holotype, RV L 1.56 mm, H 0.68 mm; LV L 1.54 mm, H 0.64 mm. Paratypes, A F, RV, L 1.56–1.60 mm, H 0.68–0.70 mm; (A-1) RV, L 1.34–1.38 mm, H 0.56–0.60 mm.

Diagnosis: Carapace medium-sized. In lateral view, elongate; with slightly arched dorsal margin; and straight (RV) or slightly concave (LV) ventral margin; posterior margin pointed at 90°. Zone of concrescence very narrow with short, straight radial pore canals. Podomeres I of maxilla I without seta. Podomere V of female appendage V with very long mid-distal seta. Furca reduced, with two rods, each rod flexible and bearing two tiny proximal setae and one terminal, short seta.

Description: Carapace medium-sized (for the genus), non-equilateral, elongate in lateral outline, narrow zone of concrescence with straight radial pore canals, calcified inner lamella narrow. Greatest height at midlength in RV and anterior to mid-length in LV. Length approximately 2.3 times maximum height. RV larger than LV. Anterior margin of both valves narrowly rounded, dorsal margin gently arched, posterior margin rounded, ending in 90° posterior angle. Ventral margin straight in RV and slightly concave in LV. Anterodorsal margin fairly straight in RV, slightly concave in LV.

Antenna I robust, thick, tapering, with seven podomeres; Podomeres II and III flexibly articulated. Antenna II compact, thick-proportioned, tightly curled, with six podomeres; podomere IV short and thick. Mandible with a broad masticatory jaw armed with one dorsal, conical tooth followed by four tricuspidate teeth and several setae. Maxilla I with three slender endites, each armed distally with a dense fringe of subequal claws, ventral endite with two proximal setae on ventral margin, other two endites without proximal setae; vibratory plate with one strahlen and ~14 to ~17 feathered setae; palp slender, flexible; podomeres I and II fused, dorsal seta of podomere I absent). Exopodite of female appendage V with seven setae; podomeres IV and V with long and thin setae, mid-distal seta conspicuously longer than other three setae. Podomere IV and V of appendage VI short; podomere VI elongate, with two subequal, medium-sized, distal claws and one short distal seta. Appendage VII thin and small; podomere V with two ventrodistal, medium-sized setae, the most ventral one shortest; and with one very short reflexed seta. Furca very small, each rod flexible and bearing two tiny proximal setae and one terminal, short seta.

Adult chaetotaxy: Antenna I 1, 2(0/.2), 3(.1/.1.), 4 (.1/.1.), 5(.1/.1), 6(.2/.3), 7(0/0:3-4). Antenna II 1(0/0:1), 2(0/0:1), Exopodite (0/0:2,1r), 3(0/5.5), 4(.2/.1c:3), 5(0/.1,1c:1.3c), 6(0/0:4c,1s). Mandible 1(0/ 5t,+5.1.), 2(0/.2), Exopodite (0/0:5), 3(0/5:1), 4(5/4), 5(.2./0:3). Maxilla I vibratory plate (1re,~14-16), palp 1+2(4/0), 3(0/0:5). Appendage V F 1, Exopodite (.3./0:4), 2, 3, 4(0/1), 5(0/0:3). Appendage VI 1(0/.1), 2(.1/.1.1.1), 3(0/.1), 4(0/.1), 5(0/.1), 6(0/0:2c,1). Appendage VII 1+2(.1/.1), 3(0/ 1), 4(0/1), 5(0/1), 6(0/0:1.1r,1). Furca 1(0/0:1.2r).

Remarks: Macromckenziea giambonini sp. nov. fits well in the description of the genus Macromckenziea except for the furca, which is more similar to the genera Macrocypris Brady, 1868 and Macropyxis Maddocks, 1990. In the new species the furca is less reduced than the furca of the other species in Macromckenziea. In this character, Mk. giambonini sp. nov. differs from all other species of Macromckenziea for which the appendages have been figured: Macromckenziea glacierae, Macromckenziea ligustica, and Macromckenziea siliquosa (Maddocks, 1990: figs 46.20–34). Additionally, Macromckenziea australiana, Mk. glacierae, Macromckenziea gregalis, Macromckenziea porcelanica, and Macromckenziea swansoni are more subtriangular, higher in relation to length than Mk. giambonini sp. nov. Furthermore, Mk. glacierae presents a more pointed posterior angle than Mk. giambonini sp. nov. Macromckenziea ligustica and Mk. siliquosa have more subparallel ventral and dorsal margins, a more straight dorsal margin and a more sinuate ventral margin than Mk. giambonini sp. nov. The valves of Macromckenziea sp. 3 from Maddocks (1990: 56), recorded from the Drake Passage (240 m), are very similar to those of Mk. giambonini sp. nov., but smaller (grey triangle in Fig. 7), with a slightly more truncated anterior margin, and Macromckenziea sp. 3 ’s antenna I is more robust, with the podomeres wider in relation to length than in Mk. giambonini sp. nov. Macropyxis andreseni and Macropyxis sonneae, from the Pacific Sector of the SO, present similar carapace outlines but are higher in relation to length, and present well-developed furca, whereas in Mk. giambonini sp. nov. the furca is reduced.