Archaeomonas jimstehrii Ehrman & Kaczmarska, 2025

Archaeomonas jimstehrii Ehrman & Kaczmarska sp. nov.

Fig. 7C–F, G View Fig .

PhycoBank ID: http://phycobank.org/105039.

Etymology: Dedicated to our son.

Holotype: DMF SEM stub 333-10, as preparation KRAM A-33, sample Łubno 4 ( Fig. 7C View Fig , SEM image of stomatocyst in anterior-lateral view). Type locality: Łubno, Poland.

Type horizon: Futoma Diatomite Member, Rupelian, lower Oligocene.

Material.—Stomatocysts with two rings of spines on secondary collar: Borek Nowy 5, Futoma 5 (DMF stub 352- 1g), 17, Łubno 3, 4 (DMF stubs 333-10 as KRAM A-33, 333- 10d, 333-10e). One ring of spines: Borek Nowy 5, Futoma 5 (DMF stub 352- 1g), 14, 20, Łubno 3 (DMF stub 342-10b). Numerous specimens encountered on each SEM stub. All Oligocene of southeastern Poland.

Diagnosis.—Collar apparatus complex; primary collar low rounded marginal rim surrounded by wide planar interannulus. Secondary collar carries one or two rings of small spines and conulae.

Description.—Stomatocysts spherical, 6.2–8.4 µm in diameter, including surface projections 0.5–0.8 µm in diameter in well preserved specimens. Pores surrounded by complex collar apparatus. Two variants of the collar were found. Primary collar in form of low rounded marginal rim ( Fig. 7C, E View Fig ) is surrounded by a planar interannulus ( Fig. 7C View Fig ), which in turn is surrounded by secondary collar consisting of two rings (variant one, Fig. 7D View Fig ) or a single ring (variant two, Fig. 7F, G View Fig 1 View Fig ) of spines and conulae ( Fig. 7E, F, G View Fig ). In variant one, the primary collar height may reach 0.4 µm with diameter 0.7– 1.1 µm. Secondary collar height may reach 0.8 µm (including projections) and 2.0–3.3 µm in diameter. Overall shape of secondary collar varies from cylindrical to obconical. Stomatocyst wall densely covered by nodules, up to 0.4 µm high, organised into a pattern similar to nodes in a regular hexagonal lattice, 13–23 papillae in 10 µm.

Metrics for variant two of these cysts overlap with those of the variant one described above: cysts 5.7–8.0 µm, pores 0.5–0.7 µm in diameter, primary collar 0.7–1.0 µm and secondary 2.0–3.3 µm in diameter, density of papillae 13–18 in 10 µm. No specimens with intermediate collar morphologies were found.

Remarks.—Our specimens share some characters with three species of the genus Archaeomonas : A. dubia Deflandre, 1933 , A. punctifera Deflandre, 1933 , and A. granulata Rampi, 1969 . All are similar in terms of cell and pore size and in their wall patterning. However, original descriptions and available illustrations show quite different collar structures in all three species. In contrast to our specimens, A. dubia ( Deflandre 1933; Deflandre and Deflandre-Rigaud 1969; Perch-Nielsen 1978) has a cylindrical, rounded rim-like collar. The collar in A. punctifera is very low, nearly indistinguishable from the structures covering the cyst surface, while the pore in A. granulata is surrounded only by a plain thick marginal rim ( Rampi 1969).

Stratigraphic and geographic range.—Rupelian (lower Oligocene) of southeastern Poland (this study).