Archaeomonas lenistriata 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 : 388-391

Archaeomonas lenistriata Kaczmarska sp. nov.

Fig. 3A–F .

PhycoBank ID: http://phycobank.org/105035.

Etymology: Refers to delicate ribbing of the cyst walls.

Holotype: DMF SEM stub 349-2, as preparation KRAM A-28, sample Borek Nowy Kawalec ( Fig. 3A , SEM image of fractured stomatocyst in anterio-lateral view).

Type locality: Borek Nowy Kawalec, Poland.

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

Material.—Stomatocysts with parallel ribs: Borek Nowy Kawalec (DMF stubs 349-2 as KRAM A-28, 349-2a, 349- 2b, 349-2c, 349-2d), Futoma 14. Concentric-ring morphology: Borek Nowy Kawalec, Brzezówka (DMF stub 333-3). At least a dozen specimens of each morphology found on SEM stubs (~20 images acquired). All from Oligocene of southeastern Poland.

Diagnosis.—Cell walls finely ribbed (may be called striae or ridges, approximately 25–35 in 10 µm) in pattern parallel to cell apical axis or showing a combination of perpendicular and parallel orientation. Collar in form of low cylinder topped with flat rim.

Description.—Stomatocysts spherical, 5.3–8.2 µm in diameter, cell walls with very fine and low ribs ( Fig. 3A, B, D, E ). Two variants of striation found: perpendicular ( Fig. 3A–C ) and parallel ( Fig. 3D–F ) to cyst apical axis (the axis connecting anterior with posterior poles of cyst). In parallel variant ribs loop around collar and descend toward posterior pole where they turn on themselves ( Fig. 3D, E ). In second variant ribs organised concentrically around collar and parallel to each other but perpendicular to apical axis ( Fig. 3B, C ). Both morphotypes of similar cell and pore size. Pores surrounded by simple cylindrical, low collar, similar in width and appearance to ribs on cyst surface, collar 0.6–0.7 µm in diameter. Ribs fine, 25–35 in 10 µm. Individual ribs up to 0.3 µm high and abaxially T-shaped when seen on best preserved specimens ( Fig. 3C, D, F ). In those specimens, rib tops nearly touch each other. In partially eroded specimens only vertical portion of “T” is preserved and so ribs appear further apart, most commonly separated by approximately 0.2 µm.

Remarks.—The overall wall general surface architecture of our specimens is similar to Archaeomonas striata Deflandre, 1933 , discussed below. Ribs looping around the collar and turning on themselves in the parallel variant are also shown in SEM images in Deflandre and Deflandre-Rigaud (1969) where they were erroneously attributed to A. striata . However, the rib density is much finer on the walls of A. lenistriata Kaczmarska sp. nov. than on the A. striata holotype or freshwater Stomatocyst 97 Duff & Smol, 1991. Furthermore, the collars of our specimens are different from those seen on LM and SEM images of the holotype and other specimens of A. striata shown by Deflandre 1933) and Perch-Nielsen (1978), leading us to conclude that our specimens represent a species new to science.

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

Archaeomonas striata Deflandre, 1933

Fig. 3G .

Material.— Six specimens from Futoma 4 ( DMF stub 349- 17a), Oligocene of southeastern Poland .

Description.—Stomatocysts spherical, 9–10 µm in diameter. Cell wall ornamented by narrow, tall ribs (up to 0.6 µm tall; 7–8 ribs in 10 µm) separated by wide depressions. Depending on cyst orientation, ribs may appear spiral, looping or nearly longitudinal between cyst anterior and posterior poles. Pores regular, 0.7 µm in diameter surrounded by a collar with obconical, concave flange, 2.2 µm in maximal diameter ( Fig. 3G ).

Remarks.— Archaeomonas striata ( Deflandre 1933; Deflandre and Deflandre-Rigaud 1969) from Jutland ( Denmark) is the most similar to our specimens. Although several specimens are shown in those sources, just one measurement is given which is for the cyst diameter (5.5 µm). The species is also reported by Perch-Nielsen (1978) and on those cysts the ribs (there called striae) also loop and split in the manner illustrated by Deflandre (1933). Her specimens are also coarsely striated (~ 9 in 10 µm), similar to the LM-documented holotype shown by Deflandre (1933) with 5–7 striae on the visible side of the spherical cell when counted on her images. Freshwater Stomatocyst 97 Duff & Smol, 1991, is somewhat similar to our specimens and those of Deflandre (1933) and Perch-Nielsen (1978) in terms of striation density (striae are called circuli in Duff and Smol 1991) but differs in collar structure; conical with ridges continuing onto the collar in Perch-Nielsen (1978) vs. cylindrical, separate and circular in Duff and Smol (1991). Furthermore, there are two SEM images shown by Deflandre and Deflandre-Rigaud (1969) attributed to this species. However, these images carry finer ribbing. At least 13 ribs can be counted on a part of the clearly visible side of the spherical cell while 5–9 is seen on the holotype in Deflandre (1933) and Perch Nielsen (1978) specimens. Admittedly, any metrics are difficult to establish when only magnifications and not scale bars are provided. Nonetheless, because of the significant difference in rib density between their LM and SEM images, we consider the two specimens illustrated in SEM as belonging to a species other than A. striata sensu Deflandre (1933) , most likely to our new species A. lenistriata Kaczmarska sp. nov.

Stratigraphic and geographic range.—Paleocene–Eocene of Mors Island, Denmark ( Deflandre 1933), Upper Eocene of the Vøring Plateau of the Norwegian Sea ( Perch-Nielsen 1978), Rupelian (lower Oligocene) of southeastern Poland (this study), and Miocene of the Subantarctic Southwest Pacific ( Perch-Nielsen 1975).

Archaeomonas stomatocysts with ridged walls

Archaeomonas genetynanii Ehrman sp. nov.

Fig. 3H .

PhycoBank ID: http://phycobank.org/105036.

Etymology: Dedicated to Eugene J. Tynan (1924–1986), who reported extensively on many microfossils including archaeomonads.

Holotype: DMF SEM stub 349-16, as preparation KRAM A-30, sample Futoma 4, fine fraction ( Fig. 3H 1 , SEM image of stomatocyst in anterio-lateral view).

Type locality: Futoma, Poland.

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

Material.—Several specimens encountered on each SEM stub from Futoma 4 (DMF stub 349-16 as KRAM A-30), 5, Oligocene of southeastern Poland.

Diagnosis.—High obconical, concave collar, cyst wall covered with short, curved ridges and prickly spines.

Description.—Stomatocysts spherical, 7.4–8.8 µm in diameter. Pores regular, 0.6 µm in diameter surrounded by obconical, concave collar ( Fig. 3H 1 ) abruptly emerging from cyst wall surface, up to 0.8 µm high and 2.9 µm in diameter at its irregular free margin. Cyst walls ornamented with short, ridges and prickly spines dispersed throughout ( Fig. 3H ). Some spines rounded, others polygonal at base. Some ridges straight, others bowed and/or branching. Spines and ridges up to 1.2 µm high, 6–8 in 10 µm.

Remarks.—Tynan described and illustrated specimens named “ Archaeomonas cf. helminthophora ” ( Tynan 1960) . He emphasised significant differences in collar structure between A. helminthophora Deflandre, 1933 , and his specimens as distinguishing characters between the two. His specimens have a collar distinctly obconical (which he called “flared”), while the holotype of A. helminthophora has a low, more cylindrical collar ( Deflandre 1933). Unfortunately, in the same publication Deflandre also diagnosed A. helminthophora cysts as having “the structure of the pore very low and flared”, contradicting his own drawing of the holotype. The low “flaring” is clearly seen on our specimens; therefore, we attribute them to A. helminthophora . Other characteristics of A. helminthophora are detailed below. The most immediately notable difference between our new species and the type specimen shown by Deflandre (1933) for A. helminthophora is the wall ornamentation. A. helminthophora cyst walls carry long ridges while our specimens and those of Tynan (1960) have a mixture of short ridges and various prickly spines.

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

Figures

Fig. 3. Archaeomonad stomatocysts from Rupelian (lower Oligocene) of Poland. A–F. Archaeomonas lenistriata Kaczmarska sp. nov., variant with concentric orientation of strips (A–C), variant with strips looping around anterior and posterior poles (D–F). A. DMF stub 349-2 (KRAM A-28), holotype, Borek Nowy Kawalec, in anterio-lateral view. B. DMF stub 333-3, Brzezówka, in anterio-lateral view. C. DMF stub 349-2 (KRAM A-28), Borek Nowy Kawalec, in anterio-lateral view. D. DMF stub 349-2 (KRAM A-28), Borek Nowy Kawalec, in anterio-lateral view. E. DMF stub 349-2 (KRAM A-28), Borek Nowy Kawalec, in posterio-lateral view. F. DMF stub 349-2 (KRAM A-28), Borek Nowy Kawalec, in posterio-lateral view. G. Archaeomonas striata Deflandre, 1933, DMF stub 349-17a, Futoma 4, in anterio-lateral view. H. Archaeomonas genetynanii Ehrman sp. nov., DMF stub 349-16 (KRAM A-30), Futoma 4, holotype, in lateral view (H1), anterior view showing details of collar and pore (H2). I, J Archaeomonas gratiosa Hajós, 1968, Futoma 5. I. DMF stub 352-1a, stomatocyst, in anterio-lateral view (I1), anterior view showing details of collar and pore (I2). J. DMF stub 352-1b, in posterior view. Scale bars 2 µm.

Fig. 1. Lithofacial map of the Menilite Formation below sheet-like shales complex (Borek Nowy member). Redrawn and modified from Kotlarczyk and Leśniak (1990, fig. 7), with permission of AGH University of Krakow Publishing, 2025.