Hartonella oblonga, 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 : 14

Hartonella oblonga sp. nov.

Figure 6 E-H zoobank.org/ B2257655-19E8-447F-A3FF-CBB4647C386C

Derivation of name. Latin, oblonga , elongated; genus neutral.

Holotype. 1HH/055, Harton Hollow, Nodular Packestones of the Off-reef Tract, Much Wenlock Limestone Formation, Homerian.

Paratype. 1HH/153, Harton Hollow, Nodular Packestones of the Off-reef Tract, Much Wenlock Limestone Formation, Homerian.

Material. 228 specimens.

Diagnosis. same as for genus.

Description. Test composed of two asymmetrical chambers that are elongate oval shaped. The dorsal chamber is elongated to tubular in shape and contains a cylindrical areal aperture at the posterior. The ventral chamber is hemispherical to conical in shape and can have either a sharp or smooth apex. The wall comprises lamellar arranged calcite tablets resembling the structure of a brick wall.

Dimensions. Overall test height of 24.1–296.8 μm and an overall test width of 22.1–258.1 μm long. Large dorsal chamber height of 17.6–111.3 μm and a diameter of 14.7–103.9 μm with a surrounding wall thickness of 0.5–19.2 μm. The smaller ventral chamber has a height of 2.9–32.3 μm and a width of 2.8–38.5 μm and the thickness of the wall surrounding the chamber is 0.5–9.7 μm thick. A septum thickness of 0.5–19.2 and an aperture width ranging from 0.9–3.2 μm.

Remarks. Specimens are different from Minourella gotlandica as they are more elongated, and their geometries are not due to longitudinal cross-sectional cuts. Variation is observed in their measurements that do not fit within the range of M. gotlandica . The apex of the ventral chamber can be either smooth or sharp. There is the possibility of establishing further species from specimens observed here, especially based on the shape of the ventral chamber.

Stratigraphical range. Lower Silurian (Homerian).

Figures

FIGURE 6. Photomicrographs of Natantesprifmata rogersi (A-D) and Hartonella oblonga (E-H) within the MWL Fm., these specimens are from Longville Stanway (A), Longville Stanway Track (B), Eaton Top (C), Moorwood Quarry (D) and Harton Hollow (E-H). (A) = N. rogersi with a prismatic dorsal chamber (DC) separated from the conical ventral chamber (VC) by a septum-like structure (ss). Apical aperture is present in the DC. (B) = N. rogersi with pyrite within the walls (pyw) of the test. Thickened walls (tw) are present around DC. Note quartz grains (qtz) within the DC infill. (C, D) = N. rogersi showing the typical kite-like shape. (E, F) = H. oblonga showing a large elongated dorsal chamber (DC) separated by a septum-like structure (ss) from its smaller globular ventral chamber. (G) H. oblonga with a pointed VC and a smoother, more oval DC. Bivalve fragment (bv) (top right). (H) An H. oblonga with a thicker than normal wall and elongated ss. Specimen of mg is neighbouring H. oblonga (bottom centre). Sparitic matrix (sp); Biosparitic matrix (bsp). All scale bars equal 50 µm.