Macropyxis undetermined

Brandão, Simone N., 2010, Macrocyprididae (Ostracoda) from the Southern Ocean: taxonomic revision, macroecological patterns, and biogeographical implications, Zoological Journal of the Linnean Society 159 (3), pp. 567-672 : 595-599

MACROPYXIS ALANLORDI SP. NOV. ( FIGS 14–17 )

Etymology: In honour of the ostracodologist Dr Alan Lord (Senckenberg Forschungsinstitut und Naturmuseum, Germany).

Material: 4 live specimens.

Holotype: 1 A M ( SNB 0149 ) (soft parts in glass slide, valves in micropalaeontological slide), ANDEEP I, # 129-2-E, ZMH K-41370 .

Paratypes: 1 A M (SNB 0115) (valves in micropalaeontological slide, soft parts in glass slide), ANDEEP III, # 16-11. ZMH K-41371 ; 1 A F ( SNB 0141 ) , ANDEEP I, # 46-7-S, ZMH K-41379 ; 1 (A-1) ( SNB 0138 ) , ANDEEP II, # 136-4-E, ZMH K-41372 .

Distribution ( Fig. 14 ): Recent. Atlantic Sector of SO (Scotia, Weddell, and Cape Basins), 3631–4727 mm.

Valve measurements: Holotype, A M RV L 2.04 mm, H 0.85 mm, LV L 2.00 mm, H 0.76 mm. Paratypes, A M RV L 2.13 mm, H 0.89 mm; A F RV L 2.04– 2.05 mm, H 0.81–0.82 mm; (A-1) RV L 1.71 mm, H 0.68 mm.

Diagnosis: Carapace medium-sized (for the genus). In lateral view, valves elongated; RV with slightly convex ventral and dorsal margins; posterior margin relatively obtuse for the genus (around 60–70°). Podomere IV of female appendage V with one long, ventral seta; podomere V with two long, subequal setae and one medium-sized, dorsal seta. Right and left male appendage V fairly symmetrical; podomere II of male appendage V with two short, modified setae (= pegs) and one reduced seta; podomere III with one ventral, reduced seta and one distal, modified seta. Furca reduced, rods short and flexible, terminal setae longer than rod itself. Hemipenis elongated, subrectangular, copulatory process short and slightly curved. Zenker’s organ with weakly sclerotized, short central tube and very large terminal bulb.

Description: Carapace medium-sized (for the genus). In lateral view, valves elongate, slightly sinuous. RV with slightly convex ventral and dorsal margins; posterior margin relatively (for the genus) obtuse (around 60–70°); anterior margin narrowly rounded; maximum height at mid-length. LV with sinuous ventral margin; trisegmented dorsal margin, but with inconspicuous angles between segments, anterior segment slightly concave; anterior margin narrowly rounded; posterior margin pointed at around 45°; maximum height anterior to mid-length. Anterior zone of concrescence medium-sized, with ramified radial pore canals; posterior zone of concrescence thin, with straight radial pore canals. RV always larger than LV.

Antennae I and II quite robust, with relatively thick and short podomeres and setae. Mandible with one conical tooth and three or four tricuspidate teeth on the masticatory process; exopodite with one reduced seta and six to eight medium-sized setae. Vibratory plate of maxilla I with two strahlen and more than 12 feathered setae; ventral endite with two basal setae; other two endites without basal seta. Podomere II of female appendage V long; podomeres III to V short; podomere IV with one long, ventral seta; podomere V with two long, subequal setae and one medium-sized, dorsal seta. Right and left male appendage V fairly symmetrical; podomere II of male appendage V with two short, modified setae (= pegs) and one reduced seta; podomere III curved at approximately 90°, with one ventral, reduced seta and one distal, modified seta. Podomere VI of appendage VI with two long, thin claws and one short, ventral seta on distal margin. Appendage VII with thin and slender podomeres; podomere II with three long setae. Furca reduced, rods short and flexible, with four to five proximal, reduced setae; distal setae thin and slender, longer than rod itself. Hemipenis elongated, subrectangular, copulatory process located in the posterodorsal part of hemipenis, short, robust, and slightly curved. Zenker’s organ with weakly sclerotized and short central tube and very large terminal bulb; vas deferens very thin.

Adult chaetotaxy: Antenna I 1, 2(0/.2), 3(.1/.1.), 4(.1/.1.), 5(.1/.1), 6(.1-2/.3), 7(0/0:4). Antenna II 1(0/0:1), 2(0/0:1), Exopodite (0/0:2,1r), 3(0/6.1c,4-5?), 4[female (.2./.2.2c,2)] [male (.2./.2.1c,2mod,1)], 5(0/.1c,1:4c,1), 6(0/0:2c,2-3). Mandible 1(0/ 4-5t,+5.1.), 2(0/.2:1), Exopodite (0/0:1r,6-8), 3(0-1/2-3:2-3), 4(5-7/0:3-5), 5(.2c./0:1c,2-4). Maxilla I vibratory plate (2re,~16), palp 1(.1/0)+2(4/0), 3(0/0:6). Appendage V 1(0/1-2.1-2), Exopodite (0/0:5-8), [female 2, 3, 4(0/.1) 5(.1./0:2)] [male 2(0/2mod,1), 3(0/.1r:1mod)]. Appendage VI 1(0/ 0:1-2), 2(.1.1.1/1), 3(0/.1), 4(.1/0), 5(1,1r/0) 6(0/0:1,2c). Appendage VII 1(.1-2/0), 2(.1.2./.1) 3(.1/0), 4(.1/0), 5(.2/ 0), 6(0/0:2,1re). Furca 1(0/0:3r.1).

Remarks: Macropyxis alanlordi sp. nov. differs from all macrocypridid species (with published illustrations on soft parts) owing to the presence of an extremely large terminal bulb and a very weakly sclerotized central tube on Zenker’s organ. One exception is Mk. sp. 19 from Maddocks (1990: 57), which present a very similar Zenker’s organ, but valves of Mx. alanlordi are conspicuously higher in relation to length, with more obtuse posterior angle. Additionally, Mx. alanlordi sp. nov. differs from other described Macropyxis species in: (1) Mx. alanlordi is more elongated, less high in relation to length than Mx. andreseni , Mx. eltaninae ; (2) Mx. alanlordi is more globulose, higher in relation to length than Mx. adriatica , Mx. adunca , Mx. amanda , Mx. antonbruunae , Mx. arta , Mx. audens , Mx. improcera , Mx. kalbi , Mx. kaesleri , Mx. labutisi , Mx. longana , Mx. rhodana , Mx. similis , Mx. simulans , Mx. tenuicauda ; (3) Mx. kornickeri presents a more protruded, elongated posterior angle than Mx. alanlordi ; (4) Mx. sapeloensis and Mx. sonneae present a more evenly rounded dorsal margin than Mx. alanlordi (with more sinuous outline); (5) Mx. thiedei is more subtriangular than Mx. alanlordi ; and (6) Mx. steinecki presents a conspicuously more sinuate outline, and more acute posterior angle. The female valve outline of Mx. alanlordi sp. nov. is very similar to Mx. amoena , Mx. adrecta , and Mx. bathyalensis , but these three species present a Zenker’s organ with a medium-sized terminal bulb, instead of a very large one.

Macropyxis adrecta seams to be the closest species to Mx. alanlordi because of similarities in the hemipenis (outline and copulatory process) and valve outline (especially in females), however both species differ, as cited above, in the terminal bulb of the Zenker’s organ. The occurrence of these species in abyssal depths of the SO ( Mx. alanlordi ) and the Southern Atlantic ( Mx. adrecta ) is possibly the result of dispersion facilitated by the northward flow of the bottom water masses formed in the SO.

Figures

Figure 14. Geographical distribution of Macropyxis and Macrosarisa species studied herein.

Figure 15. Valves and soft parts of Macropyxis alanlordi sp. nov. A, B, J, L, paratype adult male (SNB 0115, ZMH K-41371). C, D, I, K, M, holotype adult male (SNB 0149, ZMH K-41370). E, F, paratype adult female (SNB 0141, ZMH K-41379). G, H, paratype adult female (SNB 0138, ZMH K-41372). A, C, E, G, right valve external view; B, D, F, H, left valve external view; I, J, hemipenis; K–M, Zenker’s organ. Scale bars: A–H = 500 Mm; I–M = 200 Mm.

Figure 16. Valves and soft parts of Macropyxis alanlordi sp. nov. A, B, E–J, holotype adult male (SNB 0149, ZMH K-41370). C, D, paratype adult female (SNB 0141, ZMH K-41379). A, C, right valve external view; B, D, left valve external view; E, antenna I; F, maxilla I; G, H, male appendage V; I, furca; J, hemipenis. Scale bars: A–D = 500 Mm; E, G, H, J = 100 Mm; F, I = 50 Mm.

Figure 17. Soft parts of Macropyxis alanlordi sp. nov. A, D, E, paratype adult female (SNB 0141, ZMH K-41379). B, C, holotype adult male (SNB 0149, ZMH K-41370). F–H, paratype (A-1) female (SNB 0138, ZMH K-41372). A, female appendage V; B, appendage VI; C, D, appendage VII; E, H, furca; F, antenna II; G, appendage V. Scale bars: A–G = 100 Mm; H = 10 Mm.