Minyocythere tuberculata, Lord & Cabral & Danielopol, 2020

Lord, Alan R., Cabral, M. Cristina & Danielopol, Dan L., 2020, Sieve-type normal pore canals in Jurassic ostracods: A review with description of a new genus, Acta Palaeontologica Polonica 65 (2), pp. 313-349 : 336-337

Minyocythere tuberculata comb. nov.

Figs. 6E , 17 , 21 .

2012 Dolocythere tuberculata sp. nov.; Luppold 2012: 222–223; text-fig. 6a,?b; pl. 4: 9–12, pl. 6: 15, 16 [non pl. 4: 5–8 = M. macroporosa sp. nov. herein).

Holotype: BGR 16172 , RV.

Type locality: Klein Schöppenstedt, Braunschweig, Germany.

Type horizon: Sonninia sowerbyi Zone, Lower Bajocian.

Other material. —5 V, Borehole Rodewald WA 12, 404.5 m, Lower Bajocian, Witchellia laeviuscula Zone (Braun Jura γ); 2 V Borehole Hambühren WA2 150–155 m, lowermost Bajocian (Braun Jura γ). All, collective number SMF Xe 23767.

Original diagnosis. —“A species of the genus Dolocythere covered with unoriented surface swellings” ( Luppold 2012: 222).

Emended diagnosis. —A species of Minyocythere characterized by a quadrate heavily calcified carapace and strong irregular surface swellings with large sieve-pores in the depressions.

Description of NPC.—Externally large StPC-M are located in the depressions between the prominent swellings ( Figs. 6E , 17A 1 ). The median diameter for the round pores is 14.16 μm ( Table 4), which is very large when expressed in terms of the length of the supporting valve (median SI 0.025) and when this latter value is compared with those of the other three Minyocythere species (median SI 0.020). The shape of the sieve plate is generally convex and surrounded by a flat ring ( Fig. 17A 3 ). Note that for comparison with the other Minyocythere species we measured only the sieve diameter leaving out the peripheral ring. The setal pore of StPC-M is commonly visible while in most cases tubuli apertures are covered with fine sediment ( Fig. 17A 3 ). The size of the setal pore with a median of 1.4 μm and a SeP-SI of 0.095 ( Table 4) is similar to those for M. angulata ( Table 2) and M. maculosa ( Table 3). The StPC-M pores also occur with oblong shape, however, this latter shape is less frequent than the round. From the 55 pores identified on the valve in Figs. 6E and 17A 1 , 58% were round and distributed mainly on the central part of the valve, while the oblong type dominates in the peripheral area. Considering the total number of StPC-M pore density is “low”. These latter are “widely” dispersed on the valve. The DI is always above 10 μm, commonly between 30 and 40 μm. The typical two StPC-M in the antero-dorsal area are clearly visible ( Fig. 6E ).

StPC-m ( Fig. 17A 2 ) occur on the swellings of the valve. This is very clear in the LV of Fig. 6E . They can be recognized by the small sieve plate formed by a slightly depressed ring and by the large subcentral setal pore ( Fig. 17A 2 ). The median size of the round StPC-m with about 5.5 μm (SI 0.01) and the median of the setal pore of 2.76 μm (SeP-SI 0.5) are in the range of the other Minyocythere species ( Tables 1–4). We recognize in Fig. 17A 2 ten tubuli with a diameter approaching 0.3 μm. Figure 6E shows the position of 12 StPC-m.

Simple NPC were not observed on the outer sides of the valves.

Remarks.—We could not describe the pores on the interior of M. tuberculata because of lack of adequate clean material. However, for internal views of StPC Luppold (2012: pl. 4: 11) figures large StPC-M resembling those of other Minyocythere species. Luppold (2012: pl. 4: 5–8) figures juveniles of M. tuberculata that we consider to be adults of M. macroporosa sp. nov.

Stratigraphic and geographic range.—Lower Bajocian; NW Germany.

Figures

Fig. 6. Distribution of sieve-type normal pore canals (StPC) and simple normal pore canals (NPC) on the outer side of left valves of cytherid ostracod Minyocythere gen. et spp. nov. A. Minyocythere macroporosa sp. nov. from Borehole Hambühren WA2, 166 m, NW Germany, Witchellia laeviuscula Zone (Braun Jura γ), Lower Bajocian. Holotype, SMF Xe 23721, male left valve (A), detail (A), total area of A, c. 45 μm2. B. Minyocythere angulata 1 2 2 sp. nov. from Borehole Hambühren WA2, 203 m, NW Germany, Upper Aalenian (Braun Jura β). Holotype, SMF Xe 23737, male left valve (B1), detail (B), total area of B, c. 44 μm2. C. Minyocythere sp. cf. M. macroporosa sp. nov. from Borehole Rodewald WA12, 404.5 m, NW Germany, Witchellia 2 2 laeviuscula Zone (Braun Jura γ upper), Lower Bajocian. SMF Xe 23725, male left valve (C1), detail (C2). D. Minyocythere maculosa (Bate, 1963) from Hambühren WA2, 171–174 m, NW Germany, Upper Aalenian (Braun Jura β). SMF Xe 23750, male left valve. E. Minyocythere tuberculata (Luppold, 2012) from Borehole Rodewald WA12, 404.5 m, NW Germany, Witchellia laeviuscula Zone (Braun Jura γ upper), Lower Bajocian. SMF Xe 23754, female left valve. Black dots refer to macro StPC (StPC-M); white arrows point to micro StPC (StPC-m); simple NPC underlined; black arrows indicate position of the two StPC-M characteristic of Minyocythere species. Scale bars 100 μm.

Fig. 17. Cytherid ostracod Minyocythere tuberculata (Luppold, 2012) from Borehole Rodewald WA12, 404.5 m, NW Germany, Lower Bajocian. A. SMF Xe 23754, female left valve in external (A1) and internal (A4) views, micro sieve-type pore canals (StPC-m) (A2), macro sieve-type normal pore canals (StPC-M) A3), hinge, posterior (A5) and anterior (A6) parts. B. SMF Xe 23755, female right valve in external view.

Fig. 21. Stratigraphic distribution of Minyocythere angulata sp. nov., Minyocythere sp. cf. M. macroporosa sp. nov., Minyocythere macroporosa sp. nov., Minyocythere maculosa (Bate, 1963), and Minyocythere tuberculata (Luppold, 2012) in Borehole Hambühren WA2, NW Germany.

Fig. 1. Schematic cross-sections of ostracod valves, exterior to top, interior to bottom. A. NPC classification of Puri and Dickau (1969). B. StPC with sieve plate flush with external surface (1) and sieve plate in funnel-shaped depression (2).

Fig. 3. Sieve-type normal pore canals (StPC) in Aphelocythere and Camptocythere spp. A. Aphelocythere perforata Plumhoff, 1963, from Borehole Wesendorf 51a, 1031–1035 m, NW Germany, Upper Aalenian. SMF Xe 5608 (Plumhoff Collection), carapace in external right view (A1), macro StPC (StPC-M) (A2–A4). B, C. Camptocythere praecox Triebel, 1950 from Borehole Hambühren WA 2, 341 m, NW Germany, Leioceras opalinum Zone, Lower Aalenian (Braun Jura α). B. Paratype, SMF Xe 1448, male right valve in external view (B1), mid-anterior area behind marginal rim, ornamentation and pores (large and small) (B2), StPC-M with a peripheral large pore (B3), micro StPC (StPC-m) (B4). C. Paratype, SMF Xe 1448, male right valve in internal view (C1), hinge (C2), StPC-m (C3). D. Camptocythere media Triebel, 1950 from Borehole Altencelle 1014, 212/16 m, NW Germany, Upper Aalenian (Braun Jura β). Paratype, SMF Xe 1513, female left valve in external view (D1), detail, antero-dorsal area, ornamentation and pores (large and small) (D2), round StPC-M (D3), elongate StPC-M (D4), StPC-m (D5).

Fig. 2. Sieve-type normal pore canals (StPC) in Phraterfabanella spp. A, B. Phraterfabanella tridentinensis Whatley and Boomer in Boomer et al., 2001, from Rotzo Member, Calcari Grigi Formation, Trento Platform, Venetian Prealps, NE Italy, Upper Sinemurian, Lower Jurassic. A. SMF Xe 23715, female left valve, in external view (A1). Detail of antero-dorsal area (A2), macro StPC (StPC-M) (A3), micro StPC (StPC-m) (A4), and large StPC (A5). B. SMF Xe 23716, male? fragment of right valve, in internal view (B1), StPC-M in general view (B2) and details (B3, B4). C. Phraterfabanella boomeri Cabral and Colin, 2015, from Praia da Concha, Coimbra Formation, sample PCR-318, Portugal, Upper Sinemurian, Lower Jurassic. SMF Xe 23717, male carapace, in external left view (C1), StPC-M in general view (C3) and details (C2, C4, C5).