Archaeomonas gratiosa Hajós, 1968

Archaeomonas gratiosa Hajós, 1968

Fig. 3I, J View Fig .

Material.—Numerous specimens found on each SEM stub from Futoma 5 (DMF stubs 352-1a, 352-1b), Łubno 3, Oligocene of southeastern Poland.

Description.—Stomatocysts spherical, 6.0–9.0 µm, pores 0.5–0.9 µm in diameter. Collars indistinct, low, flat-rimmed and cylindrical, 0.8–1.8 µm in diameter ( Fig. 3I View Fig 1 View Fig ). Walls ornamented by sparse, thin, sharp ridges, up to 1.1 µm high in best preserved specimens. There may be 2–9 visible ridges, depending on cell orientation ( Fig. 3I View Fig 2), but most are distant from each other at 2–4 in 10 µm. Some ridges straight, running parallel to each other over a large part of the cyst surface, others shorter and slightly curved. Ridges may be positioned obliquely, spirally, or radially relative to cyst anterior-posterior axis ( Fig. 3J View Fig ).

Remarks.—Our specimens are similar to A. gratiosa with its relatively narrow cylindrical collar and ridges “not converging and connecting like in A. lefeburei Deflandre, 1933 ”, which Hajós (1968) deemed its closest relative. However, our specimens are somewhat smaller than those from the Tortonian in Hungary, being just at and below the lower range of the diagnostic size range (8–10 µm in diameter). Other similar species include A. venusta Deflandre, 1933 ( Deflandre 1933), and A. gracilis Tynan, 1960 ( Tynan 1960), but they have pronounced and obconical collars in addition to different patterns of ridges. In Archaeomonas chenevierei Deflandre, 1932d ( Deflandre 1932d), A. deflandrei Rampi, 1948 ( Rampi 1948), and A. lefeburei ( Deflandre 1933) ridges are wavy, joining and branching, unlike our cysts with singular ridges. A. deflandriana Hajós, 1968 , has an exceptionally long collar and very tall ridges.

Stratigraphic and geographic range.—Rupelian (lower Oligocene) of southeastern Poland (this study), and Tortonian (Miocene) of Hungary ( Hajós 1968).