Macropyxis alanlordi
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.
Antennula and antenna quite robust, with relatively thick and short podomeres and setae. Mandibula 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 maxillula 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 fifth limb 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 fifth limb 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 sixth limb with two long, thin claws and one short, ventral seta on distal margin. Seventh limb 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. Male copulatory limb elongated, subrectangular, copulatory process located in the posterodorsal part of male copulatory limb, short, robust, and slightly curved. Zenker’s organ with weakly sclerotized and short central tube and very large terminal bulb; vas deferens very thin.
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 fifth limb with one long, ventral seta; podomere V with two long, subequal setae and one medium-sized, dorsal seta. Right and left male fifth limb fairly symmetrical; podomere II 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. Male copulatory limb elongated, subrectangular, copulatory process short and slightly curved. Zenker’s organ with weakly sclerotized, short central tube and very large terminal bulb.
Macropyxis adrecta
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.
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, Macropyxis adunca, Macropyxis amanda, Macropyxis antonbruunae, Macropyxis arta, Macropyxis audens, Macropyxis improcera, Macropyxis kalbi, Macropyxis kaesleri, Macropyxis labutisi, Macropyxis longana, Macropyxis rhodana, Macropyxis similis, Macropyxis simulans, Macropyxis tenuicauda; (3) Macropyxis kornickeri presents a more protruded, elongated posterior angle than Macropyxis alanlordi; (4) Macropyxis sapeloensis and Macropyxis sonneae present a more evenly rounded dorsal margin than Macropyxis alanlordi (with more sinuous outline); (5) Macropyxis thiedei is more subtriangular than Macropyxis alanlordi; and (6) Macropyxis steinecki presents a conspicuously more sinuate outline, and more acute posterior angle. The female valve outline of Macropyxis alanlordi sp. nov. is very similar to Macropyxis amoena, Macropyxis adrecta, and Macropyxis bathyalensis, but these three species present a Zenker’s organ with a medium-sized terminal bulb, instead of a very large one.
Macropyxis 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 (Macropyxis alanlordi) and the Southern Atlantic (Macropyxis adrecta) is possibly the result of dispersion facilitated by the northward flow of the bottom water masses formed in the SO.
For the soft part anatomy, I follow Horne et al., 2002 (Horne DJ, Cohen A, Martens K. 2002. Taxonomy, morphology and biology of Quaternary and living Ostracoda. In: Holmes JA, Chivas AR, editors. The Ostracoda. Applications in Quaternary Research. Washington, DC: American Geophysical Union. p 5-35.).
We use the following terms for the limbs/furca from anterior to posterior with alternative names in parenthesis:
antennula (antenna I, Aa, AI, first antenna)antenna (antenna II, AII, Au, second antenna)mandibula (mandible, Md)Maxillula (first maxilla, maxilla I, maxillule, MxI, Mxu)Fifth limb (ApV, Appendage V, first thoracic leg, maxilla, maxilla I, MxI, Mxu, maxilliped, clasper (for males), P1, second maxilla, walking leg)Sixth limb (ApVI, Appendage VI, first thoracic leg, second thoracic leg, P2, walking leg)Seventh limb (ApVII, Appendage VII, cleaning limb, P3, second thoracic leg, third thoracic leg, walking leg)Male copulatory limb (eighth limb, hemipenis, uropod). Whether the Male copulatory limb is homologous to a crustacean limb remains controvertial.Furca (caudal rami, Fu, furcal rami, uropods). The homology of the podocopan furca (anterior to the anus) to a myodocopan furca (posterior to the anus) remains controversial. Similarly, the homology of the ostracod furca to the furca of other crustaceans remains controvertial.
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 AM (SNB 0115) (valves in micropalaeontological slide, soft parts in glass slide), ANDEEPIII, # 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.
2010 Brandão: Figs. 14-17.
In honour of the ostracodologist Dr Alan Lord (Senckenberg Forschungsinstitut und Naturmuseum, Germany).
Recent. Atlantic Sector of SO (Scotia, Weddell, and Cape Basins), 3631–4727 mm.
Brandão (2010)
Brandão, S. N., in press. Macrocyprididae (Ostracoda) from the Southern Ocean: taxonomic revision, macroecological patterns, and biogeographical implications. Zoological Journal of the Linnean Society.