Shi et al.—Silicified Paleoproterozoic microbiota from China
are both very small and simple. Recently, Agić et al. (2015) emended Dictyosphaera as a monospecific genus, so we assign the new specimens to D. macroreticulata.
Genus Asperatopsophosphaera Shepeleva, 1963
Type species.—Asperatopsophosphaera bavlensis Shepeleva, 1963.
Asperatopsophosphaera umishanensis Xingand Liu, 1973 Figure 10.6–10.9
1973 Asperatopsophosphaera umishanensis Xing and Liu, p. 21, pl. 2, figs. 2, 3.
Holotype.—Specimen 4-7/1858(3), illustrated by Xing and Liu (1973, pl. 2, fig. 2).
Description.—Spherical cells with a granular surface and a dense wall. Cells are 26.7–55.4 μm in diameter (mean = 35.5 μm; N = 15). Some possess uneven outlines (Fig. 10.7).
Remarks.—Granular ornamentation on microfossils from the late Paleoproterozoic were considered taphonomic signatures (Peng et al., 2007; Peng et al., 2009). On this basis, the existence of the taxon A. umishanensis became debatable. According to some previously reported materials and new specimens in the Dahongyu Formation, granular-surfaced and dense-walled A. umishanensis emerged from the Dahongyu Formation, and became more abundant upwards in the Jixian Group (Xing and Liu, 1973; Sun, 2006). Granular ornamentation on their surface is clear and uniform, which is different from cracks and foldings resulting from biological decay or diagenesis (Zhang and Liu, 1991). For these reasons, we assign these specimens to A. umishanensis.
Genus Leioarachnitum Andreeva et al., 1966 Type species.—Leioarachnitum vittatum Andreeva et al., 1966.
Leioarachnitum sp. indet. Figure 11.1–11.5
Description.—Solitary and fusiform units with a medial split that is parallel to the long axis direction. Walls are dense and opaque. Both ends taper and are rounded or blunt. Cells are 8–53 μm long (mean = 31 μm; N = 23) and 4–27 μm wide (mean = 15 μm; N = 23). Length is 2–3 times greater than the width. Some of their medial splits are open, but others are not.
Remarks.—Leioarachnitum sp. has been reported as “boat- shaped microfossils” from cherts of the Gaoyuzhuang Forma- tion, Jixian section (Cao, 2005, p. 547). The emergence of some specimens of Leioarachnitum sp. without rupture (Fig. 11.4, 11.5) in the new microbiota may demonstrate their features before excystment. Therefore, Leioarachnitum sp. is probably a different microorganism from those roll-ups of half envelope in Chuanlinggou Formation (Peng et al., 2009). Medial split- bearing “Schizofusa” from the Changcheng Group has the same fusiform characteristic, but also reveals that they are rolled up
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“half envelopes” (Yan, 1982, 1985; Yan and Liu, 1993; Peng et al., 2009). Unlike the “Schizofusa” specimens, Leioar- achnitum sp. from the Dahongyu Formation is a whole envel- ope, which is in accord with the original description of “Schizofusa” (Yan, 1982). Their medial splits have been inter- preted as excystment structures of eukaryotic algae (Lamb et al., 2009), which seems reasonable for the Leioarachnitum sp. described here.
Unnamed Form 1 Figure 11.8
Description.—Spherical cell with a broken, neck-like extension. Cells sizes 76–80 μm in diameter (N = 3). Their walls are transparent and smooth-surfaced.
Discussion.—Extensions with different morphology have been observed on Tappania, which is the characteristic microfossil in coeval strata. Detailed morphology of these specimens, espe- cially the neck-like extensions, is needed before comparing to Tappania.
Unnamed Form 2 Figure 11.9
Description.—Cells are spheroidal, occurring in pairs within a common organic wall. The outer wall is coarsely granulated. The cell pair is 25 μm in width and 41 μm in length (N = 1).
Discussion.—Cell pairs from the Bitter Spring Formation have been named Eozygion and then interpreted as a synonym of the Gloeodiniopsis (Schopf and Blacic, 1971; Knoll and Golubic, 1979). The Dahongyu specimens are different from the Bitter Spring specimens because of their granulated surface.
Unnamed Form 3 Figure 11.10
Description.—Cells are spheroidal, occurring in pairs without a common envelope. The larger cell of the pair is 33 μm in length and 30 μm in width. The smaller cell is 17 μm in length and 22 μm in width (N = 1). The outer surface is smooth.
Unnamed Form 4 Figure 11.11
Description.—Dividing cells without any common envelope. Cells are lentiform in morphology, and are connected to each other by their elongated wall in the direction of the long axis. Cells have smooth and transparent outer surfaces. Cells vary from 39.5–49 μmin length and range from 29 to 32 μminwidth (N = 1). Two cells are conjoined by their elongated outer wall.
Unnamed Form 5 Figure 11.12
Description.—Solitary spherical microfossils with a single spine-like structure on its surface. Cells vary in diameter from 30–34 μm(N = 2). Cell wall is non-transparent and smooth- surfaced. The cell wall is approximately 2 μm in thickness.
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