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720


Journal of Paleontology 89(5):695–729


Remarks.—In colonial organization and cell-shape and -size, Archaeophycus yunnanensis resembles Tetraphycus acutus, the distinction between the taxa being the absence in A. yunnanensis of distinct cell- and colony-encompassing sheaths. Although the two taxa may represent preservational variants of a single spe- cies (which would demote Tetraphycus acutus to the status of a junior synonym of Archaeophycus yunnanensis), the lack of cell- and cell tetrad-encompassing sheaths is a diagnostic char- acter of the genus Archaeophycus (Dong et al., 2009). Because of the absence of transitional forms between these species in the Chulaktau Formation, we elected to maintain the taxa as separate entities.


Genus Eoaphanocapsa Nyberg and Schopf, 1984


Type species.—Eoaphanocapsa oparinii Nyberg and Schopf, 1984.


Eoaphanocapsa molle Sergeev, 1989 (in Sergeev and Ogurtsova, 1989) Figure 14.12


Eoaphanocapsa molle Sergeev in Sergeev and Ogurtsova 1989,


p. 65, pl. 2, fig. 9; Sergeev, 1992, p. 78 and 79, pl. 26, fig. 3; Sergeev, Sharma and Shukla, 2012, p. 240, pl. 4, fig. 7.


Description.—Individual colonial cells, 12–17 μm in diameter, surrounded by single-layered envelopes, occurring in loose colonies commonly about 60 μm broad that are composed of tens of individuals. Cell-enclosing envelopes and cell walls are translucent, fine-grained, 0.5–1.0 μmthick. Some cells include a spot-like inclusion 1–2 μm in diameter.


Material examined.—A few well-preserved colonies compris- ing dozens of vesicles.


Occurrence.—Lower Cambrian, Chulaktau Formation, South Kazakhstan.


Genus Tetraphycus Oehler, 1978 Type species.—T. gregalis D. Oehler, 1978.


Tetraphycus acutus Sergeev, 1989 (in Sergeev and Ogurtsova, 1989), emend. Figures 3.11–3.20, 12.4, 12.5


Tetraphycus acutus Sergeev in Sergeev and Ogurtsova, 1989, p. 64, pl. 2, fig. 8; Sergeev, 1992, p. 80, 81, pl. 26, fig. 4.


In part: Tetraphycus amplus Golovenok and Belova, 1984. Sergeev and Ogurtsova, 1989, pl. 2, figs. 6, 12; Sergeev, 1992, pl. 26, figs. 1, 2.


Diagnosis (emended).—Spheroidal and polyhedral single- walled cells 10–20 μm in diameter that occur in dyads, triads and planar tetrads surrounded by a common sheath. Ensheathed tetrads may occur in closely associated groups.


Description.—Spheroidal or polyhedral cells enclosed by single-layered sheaths occurring in dyads, triads and tetrads


that comprise larger colonial aggregates of a few to a few tens of cell-groups. Colony morphology varies from loose clusters of tetrads to more regular cuboidal aggregations in which the tetrads commonly occur in closely packed groups encompassed in a surrounding originally mucilaginous organic matrix. Cell walls are 1 2 μm thick, translucent and course-grained; transparent outer sheaths, >0.5 μm thick, are fine-grained. Cell diameters range from 10 to 20 μm (n = 28, μ = 15 μm, δ = 2.6, RSD = 17%, DDI = 3); sheath diameters range from 12 to 22 μm. A single opaque inclusion 1to2 μm in diameter is commonly present within individual cells.


Material examined.—A few hundred vesicles in tens of colonies.


Occurrence.—Lower Cambrian: Chulaktau Formation, South Kazakhstan.


Remarks.—Modern counterparts exhibiting cell shapes and sizes similar to those of Tetraphycus acutus occur among chroococcacean and entophysalidacean cyanobacteria as well as chlorococcacean green algae, and planar tetrads like those of Tetraphycus are particularly common among coccoical colonial cyanobacteria. Two species of the genus, T. acutus and T. amplus, have previously been described from the Chulaktau Formation (Sergeev and Ogurtsova, 1989). T. amplus was originally described by from the Proterozoic Billyakh Group of the Anabar Uplift (Golovenok and Belova, 1984) but was later regarded to be a junior synonym of Myxococcoides grandis (Sergeev et al., 1995). We have therefore amended T. acutus to include this and other forms previously described as T. amplus.


Family Entophysalidaceae Geitler, 1932


Genus Eoentophysalis Hofmann, 1976 emend. Mendelson and Schopf, 1982


Type species.—Eoentophysalis belcherensis Hofmann, 1976.


Eoentophysalis belcherensis Hofmann, 1976 Figure 12.3, 12.6–12.13


Eoentophysalis belcherensis Hofmann, 1976, p. 1070, 1072, pl. 4, figs. 1–5, pl. 5, figs. 3–6, pl. 6, figs. 1–14; Hofmann and Schopf, 1983, p. 347, pl. 14-2, figs. G-J, pl. 14-6, figs. L-M, pl. 14-8, fig. C, Pl. 14-9, figs. O-Q; Sergeev, 1992, p. 81 and 82, pl.


9, figs. 1–3; Sergeev, Knoll and Grotzinger, 1995, p. 27 and 28, figs. 12.1–12.4, 12.6, 12.12–12.14, 17.1–17.10; Sergeev, 2006,


p. 196 and 197, pl. 5, figs. 1–4, 6, 12–14, pl. 8, figs. 1–10; pl. 34, figs. 1, 2, pl. 41, figs. 11–15; Sergeev, Sharma and Shukla, 2012, p. 263, pl. 10, figs. 1–10 (for complete synonymy see Sergeev, Sharma, and Shukla, 2012).


Eoentophysalis sp. Sergeev, 1992, pl. 26, fig. 6.


Description.—Spheroidal or polyhedral cells enclosed by mul- tilamellated envelopes and occurring in dyads, tetrads, octets that comprise colonies of a few tens of cell groups. The colonies typically are enclosed within a translucent envelope and vary


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