OVUMMURUS

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 : 5-6

Genus OVUMMURUS

Minoura and Chitoku, 1979

Type species. Ovummurus duoportio Minoura and Chitoku, 1979 . Upper Pennsylvanian , Kansas, USA, by original designation .

Original diagnosis (Summarised from Minoura and Chitoku, 1979). A free calcareous microorganism characteristically ovoid to ellipsoidal shaped walls. The internal chambers are oval to elliptical and are diagonally divided into two equal cavities by a septum-like structure. The test is distinctive of two narrow slit-like apertures extending symmetrically to the centre and diagonally towards both the short and long axes of the test. These apertures equate to the length of the longer axis. Along the aperture the test is elevated to give shape to slender lips surrounding the apertures.

Remarks. The shape of the aperture in almost all specimens is difficult to determine, Munnecke et al. (2000) suggest the aperture is cylindrical rather than slit-like as described by Minoura and Chitoku (1979). Areal apertures are observed in both dorsal and ventral chambers.

Stratigraphical range. Lower Silurian to Upper Permian ( Munnecke et al., 2001).

Species Ovummurus duoportius Minoura and Chitoku, 1979

Figure 3 A-D

Material. 194 specimens.

Original diagnosis. Species diagnosis the same for genus ( Minoura and Chitoku, 1979).

Description (Modified from MacNeil and Jones, 2006). Ovoid to elliptical shaped test with varying sizes based on the plane of intersection depending on a sagittal or transverse cross section. The aperture to each chamber is only visible in longitudinal cross sections, and sometimes the wall around the aperture is thickened. Sometimes flange-like features on the outer walls of an aperture are visible.

Dimensions. MacNeil and Jones (2006) report measurements of: test, 160–230 µm long, 70–100 µm wide and 65–70 µm high, the wall and septum-like structure is approximately 3–12 µm thick. Our specimen values are smaller with test ranges between 14–142 µm in height and a test width of 14–86 µm, a wall thickness of 1–14 µm and septum thickness of 1–18 µm.

Remarks. It is very difficult to obtain three-dimensional measurements, as noted by MacNeil and Jones (2006). Only the test height and length have been noted as it is near impossible with two-dimensional cross-sectional cuts to determine the threedimensional measurements. The population of Ovummurus observed was smaller than previously noted by MacNeil and Jones (2006); none of our specimens conform to the 160–230 µm test range given by them, with specimens reaching a maximum test length of 142 µm. The average test height of Ovummurus was recorded as 53 µm and width of 39 µm. However, we observed the largest overall test range between 14–142 µm in height and an overall test width of 14–86 µm. We note the largest wall thickness with a range from 1–14 µm and a septum thickness of 1–18 µm. The largest aperture observed was 3.8 µm wide.

Stratigraphic range. Lower Silurian to Upper Permian ( Munnecke et al., 2001).

Figures

FIGURE 3. Photomicrographs of Ovummurus duoportius within the MWL Fm. showing this species typical morphology and characteristic. These specimens are from: Longville Stanway (A and B) and Moorwood Quarry (C and D). (A) = Ovummurus duoportius exhibiting two chambers (C1 and C2) separated by a septal structure (ss) with an apical aperture (ap) present in C2. All specimens here are found within a sparitic (sp) grainstone matrix. (B) = O. duoportius with thickened. (C) = Longitudinal cross section showing the equal-sized chambers present within O. duoportius. (D) = O. duoportius specimen with pyrite growth within C2. All scale bars equal 50 µm.