Pentalaminamorpha radiata, Kaczmarska & Ehrman, 2023

Kaczmarska, Irena & Ehrman, James M., 2023, Parmalean and other siliceous nannofossils from the Oligocene of Polish Flysch Carpathians, Acta Palaeontologica Polonica 68 (3), pp. 441-456 : 452-453

Pentalaminamorpha radiata sp. nov.

Fig. 8A, B .

PhycoBank ID: http://phycobank.org/103789.

Etymology: From Latin radius, ray; with reference to radial ornamentation.

Holotype: DMF SEM stub 333-18, preparation KRAM A-26, sample Łubno 4 ( Fig. 8A ).

Type locality: Outcrop near the village of Łubno, southeastern Poland (shown in Kotlarczyk and Kaczmarska 1987).

Type horizon: Futoma Member, Rupelian, lower Oligocene.

Material.— Holotype only.

Diagnosis.—Cell walls silicified and contain elongate and circular constituents. Circular components take the form of a short, truncated cone. Elongated components are truncated isosceles triangles. Elevated central portion of the dorsal shield plates radially striated with margins showing mostly puncta and very short, parallel striae. Girdle plates perforated by disorganised pores.

Description.—Three radially ornamented structures found were circular. Most complete specimen in the form of a short, truncated cone with flat, ornamented top, 2.2–3.0 µm

in diameter. This structure associated with triangular band with two long sides lined by marginal ridges ( Fig. 8A ). Ridged margins of band curve in a way suggesting formation of a hollow in which conical structures would fit. Flat tops of the conical structures ornamented by short radial, punctate striae. Subtending sides carry mixture of pores and parallel striae ( Fig. 8B ).

Remarks.—The conical structure is reminiscent of the dorsal shield plates in the extant parmalean genus Pentalamina while the rimmed band to its girdle plates. In addition, the wide side of the band also has a flange similar to what is the external surface of the curved rim along the long, left side of the triangular band. A flange in this location would be expected in a pentalaminean cell to encircle the copular ventral plate. The convex profile of the radially ornamented top and structures associated with bands that curve around in a way consistent with them fitting together is again similar to the configuration of the dorsal shield plates and ventral plates in Pentalamina . Altogether, these fossilised remains suggest that they might be related to parmaleans, particularly to the family Pentalaminaceae . Diagrammatic representation of dorsal shield plates and ventral plates in extant Pentalamina is shown in Konno and Jordan (2007) while details of the single known species P. corona Marchant, 1987 in Booth and Marchant, 1987, are illustrated by Booth and Marchant (1987) and Franklin and Marchant (1995). These fossils are however notably more robust than Parmoligocena janusii gen. et sp. nov. or extant parmaleans in general. Cell size and complete cell walls remain unknown.

Stratigraphic and geographic range.— Type locality and horizon only.

Figures

Fig.8. Palaeomorphotaxa related or similar to parmaleans from Rupelian (lower Oligocene) diatomites of Łubno (A–C) and Futoma (D) Poland.A. Pentalaminamorpha radiata gen. et sp. nov. (DMF SEM stub 333-18), external surface of dorsal shield plate (arrow) and fragmented girdle plate (arrowheads). B. Pentalaminamorpha radiata gen.et sp. nov. (DMF SEM stub 333-10), internal view of the top of the central part of dorsal shield plate. C. Unnamed palaeomorphotaxon (DMF SEM stub 333-10), fragment of a cell wall containing a parmalean-like circular plate with heart-shaped depressions. D. Unnamed palaeomorphotaxon (DMF SEM stub 342-8), fragment of cell wall containing a plate with circular depressions. Scale bars 1 µm.