Leiosphaeridia Eisenack, 1958

Atfy, Haytham El, Abeed, Qusay & Uhl, Dieter, 2023, Non-pollen palynomorph and palynofacies assemblages from the Lower Cretaceous of Iraq: A glimpse into palaeobiology and palaeoenvironment, Geodiversitas 45 (11), pp. 353-366 : 357

Leiosphaeridia Eisenack, 1958 .

Leiosphaerids are considered to be algal cysts produced in the course of the reproductive phase of the life cycle; an assumption that is reinforced by the occurrence of an encystment opening ( Moczydłowska 2008). Leiosphaeridia is known from the Precambrian to the present ( Traverse 2007), and includes spheroidal to ellipsoidal, organic-walled microfossils of variable morphology, diameter, and wall thickness.

The unicellular Leiosphaeridia are produced by planktic algae, with alternating sexual or vegetative generations in their life cycle ( Moczydłowska 2008). Leiosphaerids are presumed to embody either several planktonic green algal species (e.g. Tappan 1980), photosynthetic protists ( Traverse 2007), or other microorganisms of so far unidentified affinities ( Moczydłowska et al. 2010). The eukaryotic algal origin of leiosphaerids has been suggested based on morphology, size, cell-wall, and palaeoecology ( Tappan 1980; Colbath & Grenfell 1995 and discussion therein). Based on the discussion above, and the suggestions from previous studies (e.g. Traverse 2007), they can no longer be referred to as acritarchs.

The recorded specimens from the Yamama Formation ( Fig. 3 L-O) are represented by bag-shaped, thin-walled, flattened, often collapsed, and sometimes folded palynomorphs in which the encystment opening is rarely preserved (e.g. Fig. 3O ), with a maximum diameter of 35-40 µm in average. They are preserved in relatively similar proportions in samples 09-234, 09-255, and 09-262, and completely absent in samples 09-242 and 09-243 ( Fig. 2 ).

Figures

FIG. 3. — The palynological assemblage of the Yamama Formation: A, colony of degraded Botryococcus Kützing, 1849 seen in transmitted white light. Note characteristic globular outline and lustrous yellow colour;09-262-2_P47;B, isolated coenobium of degraded Botryococcus colony seen in transmitted white light; 09-234-1_P35; C, colony of Botryococcus fluorescing under incident blue light illumination, the globular outline of the cells is very clear however, the cell cups are not clearly visible; 09-234_P35; D, Palambages sp., 09-242-3_P36; E, Palambages sp., 09-262-2_W40, arrow refers to loophole (= Schlüpfloch of Gocht & Wille 1972); F, Palambages sp., 09-262-3_G36, arrow refers to loophole (= Schlüpfloch of Gocht & Wille 1972); G, Palambages sp., 09-262-3_G40, arrows refer to loophole (= Schlüpfloch of Gocht & Wille 1972); H, marine prasinophyte phycoma of the genus Pterospermella Eisenack, 1972, 09-262-1_H53; I, dinocyst Batioladinium micropodum (Eisenack & Cookson, 1960) Brideaux, 1975, 09-234-1_R56; J, dinocyst, 09-234-1_M50; K, dinocyst, Cribroperidinium sp., 09-234- 1_N53; L, Leiosphaeridia sp., 09-255-3_G53; M, Leiosphaeridia sp., 09-262-3_T37; N, Leiosphaeridia sp., 09-234-3_S51; O, Leiosphaeridia sp., 09-255, arrow points to a possible encystment opening. Scale bars: 20 μm.

FIG. 2. — Quantitative representation of the percentages for the recorded NPPs in the studied samples: A, 09-234; B, 09-242; C, 09-243; D, 09-255; E, 09-262.