Archaeomonas sextapapillatus Kaczmarska, 2025

Kaczmarska, Irena, Ehrman, James M. & Samanta, Brajogopal, 2025, Oligocene archaeomonad stomatocysts from the Polish Central Paratethys, Acta Palaeontologica Polonica 70 (2), pp. 385-410 : 402

publication ID	https://doi.org/10.4202/app.01218.2024
persistent identifier	https://treatment.plazi.org/id/390C4800-550C-BF0A-FF89-B697AA72F8A9
treatment provided by	Felipe
scientific name	Archaeomonas sextapapillatus Kaczmarska
status	sp. nov.

Treatment

Archaeomonas sextapapillatus Kaczmarska sp. nov.

Fig. 8A, B, C, D, E–G View Fig .

PhycoBank ID: http://phycobank.org/105041.

Etymology: Reflects the hexagonal pattern of the cyst wall ornamentation.

Holotype: DMF SEM stub 352-1, as preparation KRAM A-31, sample Futoma 5, fine fraction ( Fig. 8G View Fig , SEM image of stomatocyst in anterior-lateral view).

Type locality: Futoma, Poland.

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

Material.—Several specimens encountered on each SEM stub from Borek Nowy 5, Futoma 4 (DMF stubs 349-17e, 349-17f, 349- 17g), 5 (DMF stubs 252-1h, 352-1i, 352-2c, 352-1 as KRAM A-31), 14, Łubno 2, 4, Oligocene of southeastern Poland.

Diagnosis.—Complex, conical, multilayered secondary collar with the outermost layer overlaying the secondary collar original external surface, carrying one or two rings of papilla. Primary collar in the form of narrow rim. Planar interannulus present.

Description.—Stomatocysts spherical, 6.0–8.6 µm in diameter, including papillae. Regular pore diameter 0.4–0.8 µm in well preserved specimens. Pores surrounded by complex collar apparatus. Primary collar in form of narrow marginal rim 0.6–0.9 µm in diameter, Fig. 8E View Fig ) and surrounded by a planar interannulus ( Fig. 8E View Fig ). These in turn surrounded by a gently conical secondary collar, 1.3 µm in apical and 3.4 µm in basal diameter ( Fig. 8B View Fig ). Secondary collar 0.4–1.1 µm high. In some cysts, additional layer of silica overlays secondary collar, covering it with a folded-out from the top layer that may be smooth ( Fig. 8C View Fig 1, D 1 View Fig , E) or carry small papillae on its surface ( Fig. 8A, B, F View Fig , and G). Stomatocyst wall densely covered by stout papillae in a regular hexagonal lattice pattern, up to 0.8 µm high, 13–22 papillae in 10 µm. Figures 8B, C, D, E–G View Fig show progression of buildup (or erosion) of pore-collar system with folded-over layer covering external surface of secondary collar base and cyst surface.

Remarks.—Somewhat similar to our specimens are those of A. multipunctata Rampi, 1969 , shown by Perch-Nielsen 1978). However, the illustration in Rampi (1969) presents cells with less regularly distributed papillae and a simple rim-collar. Archeomonas sextapapillatus Kaczmarska sp. nov. size and wall ornamentation are similar to A. jimstehrii Ehrman & Kaczmarska sp. nov. but the two differ in the structure of the secondary collar, clearly demonstrated in

Fig. 8A; A View Fig . jimstehrii Ehrman & Kaczmarska sp. nov. on the left and A. sextapapillatus Kaczmarska sp. nov. on the right.

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

Archaeomonas stomatocysts with smooth walls

Remarks.—We note that some freshwater cysts of similar, smooth-wall morphology are thought to represent early developmental stages of several species whose mature stomatocysts walls will eventually become different ( Duff et al. 1995; Wilkinson et al. 2001; Holen 2014). For example, the smooth-walled Stomatocyst 234 Duff et al., 1995, may represent several members of the genus Paraphysomonas De Saedeleer, 1929 ( Duff et al. 1995; Bai et al. 2023), or a species of Dermatochrysis ( Holen 2014) . There may be similar examples among species found in marine environments. Furthermore, some haptophyte species recovered from decades old marine sediments also produced cysts similar to smooth-walled chrysophyceans ( Ellegaard et al. 2016). Due to these uncertainties, we refrain from describing any new species of stomatocysts with indistinct collars and smooth walls.

Archaeomonas aff. inconspicua Deflandre, 1933

Fig. 8H View Fig .

Material.—Several specimens encountered on each SEM stub from Borek Nowy 5, 12, Futoma 5 ( DMF stub 352-1j), 17, Oligocene of southeastern Poland.

Description.—Stomatocysts spherical or slightly oblate (when infrequently observed in lateral view), 3.0–11.0 µm in diameter. Cyst external wall surface smooth, no collar. Pores conical, 0.7–2.0 µm in outer and 0.4–1.1 µm in inner diameter ( Fig. 8H View Fig ). Smaller cysts have proportionally smaller pores.

Remarks.—The current delineation of A. inconspicua is sufficiently general to encompass the smaller of our specimens. Cysts presented by Deflandre (1933) and Tynan (1960) were only 3–5 µm in diameter, although Hajós (1968) reported cells up to 7 µm in diameter. However, neither Deflandre nor Tynan provided details of pore size and structure, so we attribute our specimens to this species with reservations. There are also stomatocysts reported from freshwater environments that are quite similar to our specimens. Examples are Stomatocyst 29 Duff & Smol, 1989, emended in Zeeb and Small (1993), Stomatocyst 120 Zeeb & Smol, 1993, and Stomatocyst 42 Duff & Smol, 1989, and immature cysts which are well delineated and illustrated in Duff et al. (1995) and Holen (2014). Basic differentiation of the three cysts rests on their diameters (3–5.9 µm, 6.0–8.9 µm, and 9.0+ µm, respectively) and all fall within the size range of our specimens. See also our closing remarks at the end of the section devoted to smooth-walled stomatocysts.