Munneckella tribuscamera, 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 : 15-18

Munneckella tribuscamera sp. nov.

Figure 7 A-D zoobank.org/ 9075F00B-3A8D-4ED3-A416-8EC8EBBB1ABD

Derivation of name. Latin Tribus, three and camera - chamber, vault; genus neutral.

Holotype. 15MQ/0001, Moorwood Quarry, Crinoidal Grainstones of the Off-reef Tract, Much Wenlock Limestone Formation, Homerian.

Paratype. 17HH/0187, Harton Hollow, Crinoidal Grainstones of the Off-reef Tract, Much Wenlock Limestone Formation, Homerian.

Material. 44 specimens.

Diagnosis. same as for genus.

Description. Oval test split into three asymmetrical chambers. The large central chamber is oval to spherical in shape and is separated from the adjacent chambers by two pseudo-septa. The smaller peripheral chambers are positioned at either polar end of the large central chamber and are oval in shape. The apex of the chambers is smooth. Apertures may occur within the posterior of either, or both, of the smaller chambers. The wall of the test encompasses all three chambers and is characteristic of calcite tablets in a lamellar arrangement. Detrital clasts were observed sporadically within the chambers.

Dimensions. Measurements by Munnecke et al. (2000) gave a test height of 25–140 μm and a width, 20–90 μm. The specimens from the MWL Fm. measured a test height of 25.8–102.0 μm and a test width of 16.1–52.9 μm long. The large dorsal chamber height of 4.8–101.0 μm and a diameter of 8.1–50.0 μm with a surrounding wall thickness of 1.6–16.1 μm. The smaller peripheral chambers have a height of 1.0–96.8 μm and a width of 1.0– 52.9 μm and the thickness of the wall surrounding the chamber is 1–8.7 μm thick. A septum thickness of 1.6–17.3 and an aperture width ranging from 0.9–1.9 μm.

Remarks. Measured specimens from the MWL Fm. are comparably smaller than those observed from Gotland. Variation in thickness is observed within the three-chambered variants, in particular a thicker pseudo-septum is observed. Chamber sizes vary with some specimens having equalsized chambers and other specimens having asymmetrical chamber morphologies. There is a possibility of erecting further species based on the size variations of the chambers.

Stratigraphical range. Lower Silurian (Homerian) – Devonian (Frasnian).

Open Nomenclature

Gen. et. Sp. Indet. 1

Figure 8A

Material. 6 specimens.

Description. A bilocular test comprising of one large and one small chamber. The larger dorsal chamber has a sunken apex (heart-shaped). The smaller chamber is conical.

Dimensions. Test measurements range from: height of 61.3–71.9 μm, width of 63.2–82.7 μm. Dorsal chamber height: 35.5–48.4 μm, diameter: 58.8–71.2 μm, Thickness of the wall surrounding the dorsal chamber: 2.9–4.8 μm. Septum thickness: 1.6–3.8 μm.

Remarks. Similar to Minourella wenlockensis with its conical ventral chamber however the apex of the large dorsal chamber is slightly sunken. Due to specimen numbers, this morphotype has been left to open nomenclature because only six specimens were found and the full range of morphological variation, therefore, remains unknown. The observations could also possibly have been due to cross-sectional cuts.

Gen. et. Sp. Indet. 2

Figure 8B

Material. 2 specimens

Description. A bilocular prismatic test compartmentalised into two asymmetrical chambers. The larger dorsal chamber is pentagonal. The ventral chamber is conical.

Dimensions. Test measurements range from: height of 59.6–67.3 μm, width of 43.3–65.4 μm. Thickness of the wall surrounding the dorsal chamber: 2.9–4.8 μm. Septum thickness: 2.9–3.8 μm.

Remarks. The variant appears cubic in cross-section and could be a specimen of Natantesprifmata rogersi , however, they are cubic rather than prismatic. This morphotype has been left to open nomenclature because only two specimens were found and the full extent of the morphological variation still remains unknown.

Gen. et. Sp. indet. 3

Figure 8C

Material. 20 specimens

Description. A bilocular pyramidal test that comprises one large and one small chamber. Both the dorsal and ventral chambers are conical. The pseudo-septum separates the two chambers. No apertures were observed.

Dimensions. Test measurements range from: height of 51.0–96.8 μm, width of 60.6–96.2 μm. Dorsal chamber height: 14.4–86.6 μm, diameter: 33.7–82.7 μm, Thickness of the wall surrounding the dorsal chamber: 1.0–9.6 μm. Ventral chamber height: 1.9–38.4 μm, diameter: 1.9–38.4 μm, Thickness of the wall surrounding the ventral chamber: 1.0–6.5 μm. Septum thickness: 1.0–8.0 μm.

Remarks. This morphotype differs from any Ovummuridae specimens observed or described. Specimens may potentially be transverse cross sectional cuts through Minourella cameroni . As there is so much variation and not great enough similarity to known specimens we have left this to open nomenclature.

Gen. et. Sp. indet. 4

Figure 8D

Material. 4 specimens

Description. A bilocular test that is open ended at its posterior. The larger dorsal chamber is open at its posterior rather differently than other apertures observed from Ovummuridae . The smaller ventral chamber can be conical or globular.

Dimensions. Test measurements range from: height of 86.6–192.4 μm, width of 48.1–74.1 μm. Thickness of the wall surrounding the dorsal chamber: 1.0–5.7 μm, thickness of the wall surrounding the ventral chamber: 1.0–3.8 μm. Septum thickness: 1.0–5.7 μm.

Remarks. Similar to Minourella gotlandica and Minourella wenlockensis . Left to open nomenclature as unsure if observations are due to cross-sectional cuts, however, the wall flares out to produce flanges that have a much wider opening than typical Ovummuridae apertures, these may not be due to cross-sectional cuts.

Gen. et. Sp. indet. 5

Figure 8 E-F

Material. 24 specimens

Description (Modified from MacNeil and Jones, 2006). Globular Ovummuridae characterised by one small ventral chamber and one large dorsal chamber. Septum partly divides the large dorsal chamber into two sub-chambers, connected by a simple aperture. The septum is undulating and protrudes into the dorsal chamber to form an arcuate member that fully or partially splits the test into two chambers.

Dimensions. MacNeil and Jones (2006) noted measurements of this ovummurid variant to measure: overall test height of: 135–200 μm high, 85– 130 μm wide, wall 9–14 μm thick; small chamber 15–25 μm high, 25–40 μm wide; large chamber 95–145 μm high, 70–105 μm wide; septum 50–75 μm long; septum. The specimens from Wenlock Edge range from: height of 33.9–250.5 μm and width of 45.2–298 μm. Dorsal chamber height: 22.6–230.9 μm and diameter: 27.9–282.3 μm. The thickness of the wall surrounding the dorsal chamber: 1.0–10.6 μm. A ventral chamber height: 3.8– 19.4 μm and diameter: 3.2–43.3 μm. The thickness of the wall surrounding the ventral chamber: 1.0– 8.1 μm. Septum thickness: 1.0–8.1 μm.

Remarks. These specimens are distinct from M. gotlandica because of their larger test size and partial division of their dorsal chamber by a prominent septum. Their globular test shape distinguishes them from M. cameroni , which is conical. The Wenlock Edge material in comparison to the Hay River specimens is comparably larger. They have been left under open nomenclature because the full range of morphological variation still remains unknown.

Figures

FIGURE 7. (A) = Photomicrographs of Munneckella tribuscamera within the MWL Fm., these specimens are from Harton Hollow (A and B), Strefford Quarry (C) and Eaton Top (D). (A) = M. tribuscamera with two septum-like structures (ss) forming a three-chambered morphology consisting of a slightly larger central chamber (CC) and two smaller, often dome or cone-shaped peripheral chambers (PC). (B) = M. tribuscamera with three unequal sized chambers and varying wall thickness. An apical aperture is present in one of the peripheral chambers. (C) = Large specimen of M. tribuscamera with conical PC. (D) = M. tribuscamera. with slightly thickened thicker than normal walls. Sparitic matrix (sp); Biosparitic matrix (bsp). All scale bars equal 50 µm.

FIGURE 8. Photomicrographs of Ovummuridae left to open nomenclature within the MWL Fm. (A) = Open gen. 1, sunken apex of the dorsal chamber (DC) producing a ‘love heart’ shape. (B) = Open gen. 2, a square test shape. (C) = Open gen. 3, Triangular test shape. Dorsal chamber (DC) is separated from the ventral chamber (VC) by the septum like structure (ss). A possible transverse cross-sectional cut of M. cameroni. (D) = Open gen. 4, open DC of an elongate specimen. Possibly due to cross-sectional cuts. Flanges (fl) creating an opening at the apex of the DC. (E and F) = Open gen. 5 = Three-chambered variant (E) in which the dorsal chamber (DC) is fully split into a smaller chamber (sc) by the septum like structure (ss). A ventral chamber (VC) is still observable. A two-chambered variant (F) of this form showing various morphological differences. A third chamber is not observed. Sparitic matrix (sp); Biosparitic matrix (bsp). All scale bars equal 50 µm.