Minourella wenlockensis, Hussain & Rogers & Blackburn, 2022

Hussain, Rowshi, Rogers, Steven L. & Blackburn, Joel A., 2022, Ovummuridae (calcareous microfossils) from the Much Wenlock Limestone Formation, Shropshire, UK, Palaeontologia Electronica (a 27) 25 (2), pp. 1-24 : 9

Minourella wenlockensis sp. nov.

Figure 4 E-G zoobank.org/ AC9E3A5C-4CE9-4A24-8A14-DF56DD236761

Derivation. After Wenlock Edge , Shropshire UK – the type locality of Wenlock aged strata .

Holotype. SQ1/51. Strefford Quarry, Nodular Packestones of the Off-reef Tract, Much Wenlock Limestone Formation, Homerian.

Paratype. 3MQ/54. Moorwood Quarry, Nodular Packestones of the Off-reef Tract, Much Wenlock Limestone Formation, Homerian.

Material. 858 specimens.

Diagnosis. A species of Minourella with an overall conical test, comprising one large globular dorsal chamber and one small conical ventral chamber with apertures at the anterior end of test and a dorsal secondary aperture. The wall of the microorganism comprises linearly arranged calcite tablets.

Description. Measurements are similar to Minourella gotlandica . The dorsal chamber is globular and can be oval shaped. The ventral chamber is conical with a sharp apex. The aperture is cylindrical and in some cases conical and can be present in either or both dorsal and ventral chambers, simultaneously.

Dimensions. Overall test height of 29–212 μm and an overall test width of 17–136 μm. Large dorsal chamber height of 7–151 μm and a diameter of 10– 115 μm with a surrounding wall thickness of 0.8–23 μm. The smaller ventral chamber has a height of 7.4–150.9 μm and a width of 9.6–115.4 μm, the thickness of the wall surrounding the chamber is 0.8-16 μm thick. An aperture ranging from 0.9–10 μm.

Remarks. This morphology is mentioned and described by both Munnecke et al. (2000) and MacNeil and Jones (2006) as a variant of Minourella gotlandica , however, the apex of the ventral chamber is sharp rather than smooth, from this distinct morphological difference is appropriate to assume it is another species belonging to the genus Minourella . Separated from M. gotlandica by its conical ventral chamber as opposed to a globular test. The ventral chamber closes as an abrupt sharp apex rather than smooth one like M. gotlandica . Apertures can be present within either dorsal/ ventral chamber or within both simultaneously (see Figure 4E ).

Stratigraphical range. Lower Silurian to Upper Devonian.

Figures

FIGURE 4. Photomicrographs of Minourella gotlandica (A-D), Minourella wenlockensis (E-G) and Minorella cameroni (H) within the MWL Fm., these specimens are from Eaton Top (A, B and C), Longville Stanway Track (D and F), Moorwood Quarry (E and G) and Harton Hollow (H). (A) = M. gotlandica (mg) specimen near a bryozoan (bry) within a spiritic matrix (sp) highlighting the similarities in wall structure, (B) = M. gotlandica with a larger globular dorsal chamber (DC) separated from the smaller globular ventral chamber (VC) by a septum like structure (ss). Sparitic (sp) matrix. Specimen has a pyritic wall. (C) = M. gotlandica with an aperture (ap) within the VC. (D) = Thickened walls of the dorsal chamber with an apical aperture (ap). (E) = Sectional cut through M. wenlockensis highlighting the conical ventral chamber (VC) in contrast to the globular dorsal chamber (DC) separated by septum like structure (ss) within a sparitic (sp). (F) = Apertures present in both DC and VC. Note pyritic growth within the specimen walls. (G) = M. wenlockensis with an apical aperture (ap) within the DC. Matrix comprised of sparite. (H) = M. cameroni Longitudinal transverse sectional cut through M. cameroni exhibiting the conical nature of the test. Lateral dorsal chamber (LDC) is separated from the ventral chamber (VC) by a septum like structure (ss). Sparitic infill of the LDC and VC from the surrounding sparitic (sp) matrix. All scale bars equal 50 µm.