Archaeomonas robusta Rampi, 1969

Archaeomonas robusta Rampi, 1969

Fig. 7B View Fig .

Material.—Numerous specimens encountered on each SEM stub from Futoma 4, 5, Łubno 3, 4 (DMF stub 342-13 as B 40 0046308), Oligocene of southeastern Poland.

Description.—Stomatocysts ovate, 14.3–18.7 µm long and 11.6–14.6 µm wide, widest at approximately one quarter of cyst length from posterior pole ( Fig. 7B View Fig 1 View Fig ). Pores surrounded by externally nearly cylindrical collar with spiny margins, up to 2.3 µm high and 4.0–4.6 µm in diameter. Internally to collar walls a flat planar annulus surrounds pore, 1.2– 2.5 µm in diameter ( Fig. 7B View Fig 2). Cyst wall surface slightly undulated by elevations covered with short stout conulae loosely organised into longitudinal rows, 1–3 rows in 10 µm. Spines 1.2–1.6 µm apart.

Remarks.—There are several ovate species with spiny walls recovered from marine sediments that are somewhat similar to our specimens. However, most have distinct, long cylindrical or slightly subconical collars ( A. cayeuxi Deflandre, 1933 , A. verucosa Rampi, 1969 , A. irregularis Deflandre, 1932a ) in addition to being significantly smaller and showing different patterns of spine distribution than seen on our specimens. In contrast, the original delineation of A. robusta states that the species ought to have “…wall thicker towards the pore where it forms a kind of neck. Surface rough, slightly undulating and dotted with small, low-lying pimples” ( Rampi 1969: 7, translated from French). Although our specimens are just above the size attributed to A. robusta , the illustration of the holotype and other characters mentioned in the original species description fit them well. This species has been infrequently reported since its erection. Perch-Nielsen (1978) substantiates it with an image of a non-ovoid cyst with a long, narrow cylindrical collar, contrasting with the species delineation.

Stratigraphic and geographic range.—Eocene of the Kreyenhagen Formation, California ( USA; Rampi 1969), Eocene of the Vøring Plateau of the Norwegian Sea ( Perch-Nielsen 1978), and Rupelian (lower Oligocene) of southeastern Poland (this study).

Archaeomonas stomatocysts with equidistant wall protrusions

Remarks.—Equidistant distribution of wall surface protrusions (scabrae, papillae, conulae or spines) is relatively frequent among stomatocysts. Such stomatocysts are known from marine sediments since the Paleocene. For example, Archaeomonas dubia , A. punctifera , and A. granulata all share a quincunx, hexagonal or other grid-based pattern of wall ornamentation ( Deflandre and Deflandre-Rigaud 1969). Similarly, such stomatocysts are also known from extant inland and predominantly freshwater environments ( Duff et al. 1995; Wilkinson et al. 2001). They all differ from our three new species not only in collar structure (Stomatocyst 117 Zeeb et al., 1990; Stomatocyst 210 Duff & Smol, 1994; Stomatocyst 31 Duff & Smol, 1989; Stomatocysts 65, 67, 89 Van de Vijver & Beyens, 2000) but also in the size and shape of the surface structures (Stomatocyst 73 Duff & Smol, 1991) and their density (Stomatocyst 352 Zeeb & Smol, 2001 in Wilkinson et al.

2001).