Bythopussella brandtae, Brandão, Simone N., 2008

Brandão, Simone N., 2008, New species of Bairdioidea (Crustacea, Ostracoda) from the Southern Ocean and discussions on Bairdoppilata simplex (Brady, 1880),? Bairdoppilata labiata (Müller, 1908) and Bythopussella aculeata (Müller, 1908) *, Zootaxa 1866, pp. 373-452 : 435-442

Bythopussella brandtae sp. nov.

( Figs. 43 , 44, 45.A–D, 46, 47.A–F)

2005? Anchistrocheles ? cf. A.? aculeata Müller, 1908 , Mazzini: 20, Figs. I–K.

Etymology. Named in honour of Prof. Dr. Angelika Brandt, who coordinated the ANDEEP project.

Material: 20 live specimens, 203 V. Holotype: 1 A M (SNB 0281), ANDEEP II, # 133–3–E, ZMH K­ 41320. Paratypes: 3 A F (SNB 0 280, SNB 0 282, SNB 0283), 8 A, 1 (A­1), 79 V, 11 RLV, ANDEEP II, # 133–3–E, ZMH K­ 41358; 3 A M (SNB 0661­0663), 3 A F (SNB 0658­0660), 15 RV, 17 LV, 8 RLV, 54 V, ANDEEP II, # 132–2–S, ZMH K­ 41322; 1 A F (SNB 0678), ANDEEP III # 133–2, ZMH K­ 41323.

Distribution. NW Weddell Sea, Southern Ocean (Atlantic Sector), 1123 to 2084 m.

Measurements ( Fig. 43 ). Holotype, LV, L 1.00mm, H 0.56mm; RV, L 1.00mm, H 0.53mm. Paratypes, LV, L 1.08mm, H 0.62mm; A F L 1.05–1.08 mm, H 0.60–0.62mm; A M L 1.00– 1.05 mm, H 0.56–0.57mm; A (sex indeterminate) L 0.95–1.12 mm, H 0.53–0.64mm; (A–1) L 0.80–0.87mm, H 0.44–0.49mm; (A–2) L 0.67 mm, H– 0.39 mm.

Diagnosis. Valves large, bairdiid in aspect, with conspicuous lateral punctation; both valves with 8 to 10 short spines on anterior margin; LV with 1 long spine on posterior margin. Podomere VI of AII with 1 long claw, and 1 medium­sized and 1 small setae in males; females present 1 long claw, and 1 medium­sized and 2 small setae. MxI with 7 strahlen. Distal claw of podomere V of ApV robust. Podomere V of ApV to VII with 1 long terminal claw, and 1 vestigial seta. Fu with 2 medium­sized claws, and 2 medium­sized setae. Genital lobe subcircular with short, internal tube. Hemipenis with sub­hemispherical basal capsule, which is distally beaked; short, curved copulatory tube, and one rigid, chitinized, flexibly articulated medial process ending in a slender hook.

Description. Valves large, with bairdiid outline in lateral view; lateral surface of valves punctate, except on the anterior and the ventral areas in adults; in juveniles just the central area is punctate; numerous long, conspicuous sensilla present. Dorsal margin of both valves tri­segmented, in LV more smoothly rounded than in RV, posterodorsal segment concave; anterior margin of both valves with 8 to 10 short spines; ventral margin sinuous with conspicuous concavity in mouth region and upswung posterior. Adductor muscle scars pattern with 3 anterior and 1 posteroventral scars. Calcified inner lamella and zone of concrescence fairly broad with numerous, straight radial pore canals, vestibules constricted. Radial pore canals simple, with or without rims. Male valves not as long as, and less high in relation to length than female valves. In dorsal view, carapace compressed, sub­hexagonal, maximum width slightly posterior to mid­length.

Labrum and hypostome anteroventrally prolonged. AI robust with 7 podomeres, none fused; 1 of the terminal setae very long; chaetotaxy 1(0/0), 2(1/0), 3(1/0), 4(0/0­1), 5(2­3/1), 6(1­3/1), 7(0/0:?2­?5). AII podomeres elongated, especially podomere V; exopodite with 1 long and 1 short setae; podomere VI with 1 long claw, and 1 medium­sized and 1 small setae in males, females present 1 long claw, and 1 medium­sized and 2 small setae, all setae articulated; chaetotaxy 1(0/0:1int), 2(0/1), 3(0/.1­3r.1), 4(.2/0), 5(.2pq./.1), 6(0/ 0:1,1c,0­1,1). AII and ApV to VII terminal claws with tiny terminal hooks. Md and MxI also very elongate. Md with 4 trifurcate teeth on masticatory base, exopodite with 3 long setae; palp chaetotaxy 1(0/.1.: 1i), 2(.1.1/ 1:0­ 1 i), 3(.1.1.0­1/1­2: 1i), 4(.1/0:1c,?4). Vibratory plate of MxI with 7 strahlen and around 20 feathered setae; palp with 2 dorsal, 1 ventral, and 3 distal, medium­sized setae; 3 endites without proximal seta. ApV with quite short podomeres, vibratory plate with 4 strahlen and around 8 feathered setae; chaetotaxy 1(.1.1.0­1.0­ 1.2/0), 2(.2/0), 3(0/0), 4(.1r/0), 5(0/0:1c,1r). ApVI and ApVII without setae on exopodite (=ventral setae); chaetotaxy 1(.1.1.1r/0), 2(.2/0), 3(0/0), 4(.1r/0), 5(0/0:1r,1c). Fu with 1 large and 1 medium­sized claw, and 2 medium­sized setae. One short seta between both Fu rods. Brush­shaped organ symmetrical. Genital lobe subcircular, with short internal tube. Hemipenis with sub­hemispherical basal capsule, which is distally beaked; the short, strongly chitinized, curved copulatory tube extends less than the distal part of the basal capsule; plus one rigid, also chitinized, flexibly articulated process ending in a slender hook.

Remarks. Warne (1990) described the genus Bythopussella in order to accommodate species previously assigned (based on soft parts) to the genus Anchistrocheles , but which present a bairdiid carapace. Bythopussella brandtae sp. nov. fits exactly this last description: with bairdiid carapace and anchistrocheline soft part characters – (1) anteroventrally prolonged labrum and hypostome, forming a flexible jawlike snout; (2) elongated mandible and maxilla I; (3) appendages VI and VII lack setae on exopodite (= ventral setae on basal podomere); (4) distal setae of antenna II and appendages V to VII terminated by tiny hook.

Contrary to the wide variation observed in B. malyutinae sp. nov., Bythopussella brandtae sp. nov. shows very little, if any, intraspecific morphological variability in valves and hemipenis ( Fig. 44.A–I, P–V), male specimens collected from both stations (at 1123 and 2082 m depth) present the same hemipenis outline, beaked basal capsule, equal relative length of copulatory tube and elongated process.

Bythopussella brandtae sp. nov. is very similar to Bythopussella microguttata , but the former species is higher in relation to length; and presents 1 long posterior spine, larger anterior spines, more arcuate dorsal margin in LV, rounder dorsal margin in RV, and less marginal pore canals anteriorly and posteriorly (appr. 30 instead of 44 and 41).

Valves of B. brandtae sp. nov. are similar in shape and size to B. aculeata ( Müller, 1908) , which was recorded only from the Indic sector of the Southern Ocean (65°S, 90°E, 385m) ( Fig. 45.P–S). The new species can be distinguished from B. aculeata by the following characters: 1) ventral margin of both valves is more sinuous in the new species (especially RV); 2) the new species is more compressed in dorsal view; 3) the punctation is more widely distributed and deeper in the new species; 4) hemipenis – a) in the B. brandtae sp. nov. the hemipenis is sub­hemispherical (more elongate in B. aculeata ) and has a large, elongated, strongly chitinized process perpendicular to dorsal hemipenis margin and terminating in a hook, while B. aculeata presents a shorter, L­shaped process; b) the copulatory rod of the new species is curved at approximately 90° instead of 180° in B. aculeata .

The LV of Anchistrocheles ? cf. A.? aculeata from the South Tasman Rise illustrated by Mazzini (2005, Fig. 10 .I–K) is similar to B. brandtae sp. nov. but presents greater height/length ration, slightly more rounded dorsal margin, and lacks the anterior and posterior spines (or they might be broken).

The valves of Anchistrocheles angulata (Brady, 1870) sensu Brady (1880, Pl. 11.5a–d) have a distinct lateral and dorsal outline: (1) lateral – more sub­reniform, without the long spine on the posterior edge of LV; (2) dorsal – less inflated, more sub­oval outline. Anchistrocheles angulata ( Brady, 1880) sensu Maddocks (1976, Pl. 7.11) has a very similar hemipenis to Bythopussella brandtae sp. nov., especially in the copulatory tube and chitinized process, but the distal part of the basal capsule is not beak­shaped in the first species. Furthermore, antenna I has 7 articulated podomeres in the new species and only 6 podomeres in Brady’s species ( Maddocks 1976, Pl. 7.2); antenna II of the new species is more elongated, especially podomere V; appendage V presents about 8 feathered setae (instead of 2). A comparison of the carapace morphology of Anchistrocheles angulata ( Brady, 1880) sensu Maddocks, 1976 is not possible because the carapace of this specimen was decalcified and consequently no illustrations of the valves were provided.

Bythopussella brandtae sp. nov. is similar in outline to Anchistrocheles ? sp. aff. A. angulata ( Maddocks 1969:113, Fig. 60M) but lacks the long spine on the anterior of LV.

Anchistrocheles ? n. sp. from Triebel (1960, Pl. 20.44a, b) from Bass Strait, has a more subreniform outline and lacks the long, posterior spine on the LV.

The shallow water species Anchistrocheles mcquadei Maddocks, 1976 , Anchistrocheles barnharti Maddocks, 1976 and Anchistrocheles hartmanni Maddocks, 1976 from the Caribbean, Anchistrocheles acerosa (Brady, 1868) from Northeastern Atlantic, Anchistrocheles bradyi Scott, 1905 and Anchistrocheles fumata Brady, 1890 both from the Indian Ocean, are very distinct from the new species herein owing to their valve subreniform outline in lateral view.

The presence of these five morphologically similar species around Antarctica – B. brandtae sp. nov., B. microguttata , B. aculeata , A?. cf.? A. aculeata G. W. Müller, 1908 (from Mazzini, 2005) and B. sp. aff. B. brandtae sp. nov. (herein) – indicates that even with the circum­antarctic current, which favours the migration and consequent genetic flux among populations located around Antarctica, podocopid species are probably not able to migrate in the velocity and frequency necessary to keep the genetic flux and to prevent speciation. It also indicates that many of the species previously believed to have a circum­antarctic distribution could actually be groups of species. The possibility of a vicariant speciation due the isolation of several populations as a consequence of larger ice extension during glaciation periods is herein considered improbable since these species also occur in the continental slope, and it is very improbable that the water column was frozen to such depths.

Figures

FIGURE 10.? Bairdoppilata sp. 1 aff.? B. labiata. Legend: A – K, A M (USNM 121348); L – O, A F (USNM 121347). A, C, LV hinge; B, LV, iv; D, F, RV hinge; E, N, RV iv; G, I, normal pore canals; H, posterior of LV, ev; J, adductor muscle scars of LV; K, anterior of LV, ev; L, posterior of RV, ev; M, O, RV lateral surface. Scale bars: A, C, D, F, O, 10 µm; B, E, N, 500 µm; G, I, 1 µm; J, H, L, 100 µm; K, M, 50 µm.

FIGURE 43. Length: height scatter plot of the valves of Bythopussella aculeata (Müller, 1908), Bythopussella brandtae sp. nov. and Bythopussella sp. aff. B. brandtae sp. nov.