Minyocythere maculosa ( Bate, 1963 )

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 : 332-336

publication ID	https://doi.org/ 10.4202/app.00632.2019
persistent identifier	https://treatment.plazi.org/id/03C7A65F-C95D-FFFB-FFC8-CEB1886BFEEC
treatment provided by	Felipe
scientific name	Minyocythere maculosa ( Bate, 1963 )
status

Treatment

Minyocythere maculosa ( Bate, 1963)

Figs. 5C, D, 6D, 14, 15, 16, 21.

1941 Leptocythere View in CoL ? sp.; Triebel 1941: 333, pl. 7: 71, 72a, b.

1949 “Ostr. 99”; Brand 1949: table 14.

1962 “ Lophodentina ”? sp. 99; Brand and Fahrion 1962: 136–137, pl. 20: 25; table 9.

1963 Dolocythere maculosa sp. nov.; Bate 1963: 205–206, text-figs. 8, 9, pl. 12: 1–11.

Type material: Holotype BMNH Io. 609; paratypes BMNH Io. 610–613 and Io. 856–875, for original description see Bate (1963: 205–206).

Type locality: Eastfield Quarry , South Cave, East Yorkshire, UK .

Type horizon: “Cave Oolite”, Bajocian .

Material. — UK: 9 C, 35 V, 1 V juvenile (near topotypic), collective number SMF Xe 23767, Everthorpe Quarry, South Cave, “Basement Beds”, Bajocian. NW Germany: 29 V including 2 V ( SMF Xe1227 of Triebel 1941), Borehole Rodewald WA2, 390– 395 m, Lower Bajocian, Witchellia laeviuscula Zone (Braun Jura γ); 2 C, 51 V, 2 V juvenile, Borehole Hambühren WA2 171–174 m, uppermost Aalenian (Braun Jura β); 2 C, 2 V, Borehole Lingen 330, 1014–1020 m, Lower Bajocian, Witchellia laeviuscula Zone (Braun Jura γ); 1 V, Borehole Fuhrberg 26, 178.75– 179.15 m, Sonninia “ sowerbyi ” Zone, Lower Bajocian.

Original diagnosis. —A species of Dolocythere , slightly constricted in mid-dorsal/mid-ventral region and ornamented with large circular pits scattered over carapace ( Bate 1963: 205).

Remarks. —The British type material is not very well preserved but Bate (1963: 205–206) provides a full description including details of hingement and marginal pores that match the definition herein of Minyocythere and its type species. He noted ( Bate 1963: 206) “Surface of carapace covered with large, circular, rather shallow pits, within each of which is a large normal pore canal.” The nature of the normal pore canals as sieve-type was not mentioned, doubtless due to preservation. Our South Cave material revealed two types of StPC. StPC-M are visible on the exterior of the valve ( Fig. 14A View Fig 1 View Fig ), majority of round type. There are few oblong pores especially at the periphery of the valve. The valve in Fig. 14A View Fig 1 View Fig shows approximately 70 round pores and 3–4 oblong ones. These pores are sunken in slight depressions ( Fig. 14A View Fig 2 View Fig ). The median diameter is 15.5 μm (n = 12) and the SI is 0.023 (15.5/650). Diameter of the setal pore is in range of 1.2 μm and is peripherally located ( Fig. 14A View Fig 2 View Fig ). The DI varies between 25–45 μm (n = 5), i.e. a “widely” dispersed pore pattern. On the inner side of the valve the StPC-M display a smaller size as compared to the outer side, namely less than 10 μm diameter. Figure 14B View Fig ( UK material) displays for the inner side of the female valve the positions of the pore apertures around the central AMS; their diameter is less than 10 μm (cf. Fig. 5D, female, German material). The StPC-m on the valve exterior ( Fig. 14A View Fig 3 View Fig ) display a diameter in the range 5–6 μm. The setal pore has a subcentral position and is larger than those of the StPC-M. For example, in Fig. 14A View Fig 3 View Fig the diameter of the StPC-m is 5.41 μm and the setal pore is 2.33 μm. Around the setal pore 16 tubuli with diameters between 0.3–0.4 μm are disposed in two incomplete rows.

Sexual dimorphism was not recognized by Bate (1963), but it is less well developed in our material than in M. macroporosa sp. nov or M. angulata sp. nov.

The British material is larger than the German specimens presumably for reasons of a more favourable or stable environment or nutrients ( Fig. 15 View Fig ).

Triebel’s (1941) discussion of his “ Leptocythere ? sp.”, which first drew our attention to the early record of StPC, is translated in Appendix 2. We have analysed NPC in Triebel’s material (Figs. 5D, 6D, 14C–E, 16, Table 3) to

) mm in (Height

Length (in mm) Length (in mm)

compare with the British topotype material of M. maculosa . Figure 6D View Fig shows a simple, peripherally located NPC with a diameter of about 2.5 μm. The StPC-M in most cases are round and large and located in slightly depressed alveoles

Fig. 14C View Fig 2 View Fig , C 3 View Fig ). There are a few oblong pores peripherally. The median diameter of the StPC-M apertures on both sides of the valve is about 12 μm and those of the SI 0.02 ( Table 3). Setal pores ( Fig. 14C View Fig 2 View Fig , C 3 View Fig ) display median diameter values between 1.3–1.5 μm ( Table 3). The StPC-M on the inner side of the valves of Triebel’s north German material are much larger than those of the UK topotype valves. The StPC-M display numerous tubuli with a diameter of 0.3–0.4 μm; median values are in the range 90 to 106 depending on the side of the valve observed ( Table 3). Density of StPC-M on the lateral side of the valve is “low”, namely in the range of 50 to 65 pores, e.g., the male valve in Fig. 14C View Fig 1 View Fig displays 55 pores, while the female ( Fig. 14D View Fig 1 View Fig ) has 52. The pores are widely spaced, with DI values similar to those of the topotype material. The two characteristic StPC-M in the antero-dorsal area ( Fig. 6D View Fig ) are visible on both sides of the valve. The StPC-m display a small size with median values for the diameters between 6–4 μm, depending of the side of the valves observed ( Table 3). The small sieve plate displays between 12–23 visible tubuli around a large setal pore, with a median value of about 2.5 μm. The median value of SeP-SI is 0.45 ( Table 3). We identified on the various valves between 8 and possibly 14 StPC-m with very stable location. Figure 6D View Fig shows this pattern of “stable” location as compared to the apparently “random” distribution of the StPC-M type.

Figure 16 View Fig illustrates the development of juvenile valves of M. maculosa , the stage A-2 (L = 0.378), A-3 (L = 0.290), and A-4 (L = 0.240), using Triebel’s SMF material ( Fig. 16A View Fig 1, B 1, C 1 View Fig ). On these valves we analysed the size and the number of tubuli for StPC-M and StPC-m. In the A-2 stage ( Fig. 16A View Fig 2 –A View Fig 5), the StPC-m ( Fig. 16A View Fig 2 View Fig ) displays a size of about 3.7 μm with a setal pore of about 2 μm and 12 tubuli with a diameter of 0.3 μm. In this respect the StPC-m of the A- 2 juvenile resemble those of the adult type ( Figs. 14C View Fig 2 View Fig , C 4 View Fig , Table 3). The StPC-M in the Fig. 16A View Fig 3 View Fig , A 4 View Fig display a sieve-type much smaller than in the adult, diameter in Fig. 16A View Fig 4 View Fig is 5.5 μm and number of tubuli is about 40 with diameters of about 0.3 μm. The setal pore has a diameter close to those of the adults, namely 1.15 μm. The number of tubuli on the inner side of the A-2 ( Fig. 16A View Fig 5) valve is apparently in the range of those of the outer side seen in Fig. 16A View Fig 4 View Fig . In the A-4 valve we note that the StPC-m ( Fig. 16C View Fig 2 View Fig ) has a diameter of 3.6 μm, the setal pore has 1.5 μm diameter. We noted 12 tubuli with a diameter of 0.3 μm. The StPC-M ( Fig. 16C View Fig 3 View Fig ) displays a larger size than the StPC-m, with diameter 4.6 μm and number of tubuli about 26. The A-3 details in Fig. 16B View Fig 2 View Fig , B 3 View Fig are not very significant but they contribute to the following interpretation of the development of the two types of StPC, namely the StPC-m approaches full development in A-2 for its size, the setal pore diameter and number of tubuli, whereas the StPC-M in the A-2 displays a size and number of tubuli which represents about the half of the dimension and the number seen in the adult pore.

Stratigraphic and geographic range.—Bajocian, Middle Jurassic; NW Europe. Bate (1967: Table 4) summarises the occurrence of M. maculosa in a number of Bajocian age units in Lincolnshire and eastern Yorkshire, UK, but the age range in terms of ammonite biostratigraphy is not well-defined as a consequence of variable marine connections ( Cope et al. 1980; Rawson and Wright 1995); Lower Bajocian Witchellia laeviuscula –Otoites sauzei zones is a best estimate. Our German material from boreholes is also not closely age-constrained but the material studied is from the Upper Aalenian to Lower Bajocian, although “ Lophodentina ”? sp. 99 of Brand and Fahrion (1962) is reported as restricted to the Sonninia “ sowerbyi ” Zone, Lower Bajocian.