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Schopf et al.—Berkuta and Chulaktau microbiotas


from loose clusters of gloeocapsoid cells to more regular spheroidal aggregations. Outermost envelopes enclosing indi- vidual cells are fine-grained and ~0.5 μm thick; inner envelopes are medium- to coarse-grained, ~1.0 μm thick; cell diameters range from 3 to 10 μm(n = 80, μ = 6 μm, σ = 1.5, RSD = 26%, DDI = 5). A single opaque inclusion 0.5–1.0 μmin diameter is commonly present within individual cells.


Material examined.—Approximately 200 cells in several colonies.


Occurrence.—Widely distributed in Paleo-, Meso-, Neoproter- ozoic, Ediacaran, and Lower Cambrian chert-permineralized organic-walled assemblages.


Remarks.—A taxon particularly common in Paleo- Mesoproterozoic microbial assemblages, Eoentophysalis is morphologically highly variable, the several stages of its com- plex life cycle being subject to varying degrees of preservational alteration (Hofmann, 1976; Golubic and Hofmann, 1976; Hofmann and Schopf, 1983; Knoll et al., 1991; Sergeev at al., 1995, 2012; Sergeev, 2006). In many Proterozoic deposits, colonies of E. belcherensis comprise crustose stratiform lami- nae. However, those of the Chulaktau population occur only as isolated gloeocapsoid palmelloid colonies, presumably as a result of the dynamic, highly energetic environment evidenced by the Chulaktau phosphoites (Kholodov and Paul, 1993a, 1993b, 1994)


Family Xenococcaceae Ercegović, 1932


Genus Synodophycus Knoll, 1982, emend. Knoll, Swett and Mark, 1991


Synodophycus sp. Figure 14.7–14.9


Synodophycus sp. Sergeev and Ogurtsova, 1989, pl. 2, fig. 7; Sergeev, 1992, pl. 26, fig. 8.


Description.—Aggregates of equidimensional 10- to 15-μm diameter cells, commonly surrounded by single or multilayered envelopes and clustered in irregular spheroidal colonies 40– 50 μm across composed of 16–64 individuals. Cell walls are <0.5 μm thick, translucent and fine-grained; when present, sur- rounding sheaths are single- or multilayered, transparent, fine- grained and up to 2 μm thick.


Material examined.—A few colonies comprising tens of individuals.


Remarks.—Synodophycus has been assigned to the cyano- bacterial pleurocapsalean family Xenococcaceae (Knoll et al., 1991). Although not a widely reported genus, many colonial fossils assigned to other cyanobacterial genera may actually be taxa of this genus.


Incertae Sedis Genus Berkutaphycus new genus


721


Type species.—Berkutaphycus elongatus gen. sp. nov. by monotype.


Diagnosis.—Single-walled unbranched cylindrical filaments separated by cross walls into cell-like segments having lengths greater than widths. Filaments can be broken into short cylind- rical bodies, cask-like fragments having rounded ends, or spheroidal vesicles. The filaments occur singly or in groups of tangled subparallel-oriented individuals.


Etymology.—From the name of Berkuta settlement, situated near the source of the Kyrshabakta Formation Berkuta Member (Lower Dolomite) holotype-containing fossiliferous chert and with reference to cyanobacterial/algal affinity.


Berkutaphycus elongatus new species Figures 4.1–4.20, 13.6–13.8, 13.11–13.16


Siphonophycus sp., Sergeev and Ogurtsova, 1989, pl. 2, figs. 2, 3.


Palaeosiphonella sp., Sergeev and Ogurtsova, 1989, pl. 2, fig. 1; Sergeev, 1992, pl. 24, fig. 3.


Siphonophycus sp4., Sergeev, 1992, pl. 24, figs. 1, 2, 4, 10.


Diagnosis.—Single-walled cylindrical filaments, 11–70 µm broad, commonly separated by cross- or end-walls into seg- ments 70–80 µm long. Filaments can be broken into short cylindrical bodies 25–70 × 40–205 µmhaving rounded ends, or into 25- to 60-µm diameter spheroidal vesicles.


Description.—Single-walled unbranched cylindrical filaments separated by cross walls into cell-like segments having lengths larger than widths. Filaments can be broken into short cylind- rical bodies, cask-like fragments having rounded ends, or spheroidal vesicles. The filaments occur singly or in entangled groups of subparallel-oriented individuals. Filaments are 11– 34 µm in diameter (n = 80, μ = 23 μm, σ = 5.1, RSD = 22%) and up to 500 µm long (incomplete specimen). Filament fragments, equant to more elongate cylindrical bodies, range from 25 to 70 µm in width and 40 to 205 µm in length, whereas the diameters of isolated vesicles range from 25 to 60 µm; dia- meters of the entire population range from 11 to 70 µm(n = 85, μ = 24 μm, σ = 9.2, RSD = 38%). Filament walls are translu- cent, medium-grained, and 1 to 2 µm thick. In the Berkuta cherts, the interiors of Berkutaphycus elongatus filaments commonly contain elongate or actinomorphic anthraxolite-like degraded cytoplasmic remnants.


Etymology.—From the Latin elongatus referring to the elongate to the distinctive cylindrical elongate shape of the cell-like segments.


Holotype.—Figure 13.11, 13.12, GINPC192; Lower Cambrian, Nemakit-Daldynian Stage; Kyrshabakta Formation, Lower Dolomite, locality 27, the Koksu River basin.


Material examined.—More than 500 well-preserved specimens.


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