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724


Journal of Paleontology 89(5):695–729


Genus Cymatiosphaera Wetzel, 1933, emend. Deflandre, 1954 cf. Cymatiosphaera sp.


Figure 14.1, 14.2, 14.4, 14.5


Description.—Spheroidal vesicles, subcircular in cross-section and 55 to 65 µmin diameter, having medium-grained 1- to 2-µm thick walls the surface of which is folded into distinctive poly- gonal fields 5–7 µm broad and 12–17 µm long.


Material examined.—Two well-preserved specimens.


Remarks.—Some six species of this widely occurring planktonic taxon have been reported from Lower Cambrian microfossil assemblages. However, because most such taxa have described on the basis of compression-preserved rather than permineralized specimens, it is difficult to compare them with the Chulaktau specimens recorded here to which we therefore do not assign a specific epithet.


Genus Leiosphaeridia Eisenack, 1958, emend. Downie and Sarjeant, 1963, emend. Turner, 1984, emend. Yankauskas, 1989


Type species.—Leiosphaeridia baltica Eisenack, 1958.


Leiosphaeridia minutissima (Naumova, 1949), emend. Yankauskas, 1989 (in Yankauskas, 1989) Figure 13.10


Leiotriletes minutissimus Naumova, 1949, pl. 3, fig. 4. For complete synonymy, see Yankauskas, 1989.


Leiosphaeridia minutissima Yankauskas in Yankauskas, 1989,


p. 79 and 80, pl. 9, figs. 1–4, 11; Grey, 2005, p. 185, fig. 68D; Vorob’eva, Sergeev, and Knoll, 2009, p. 185, fig.


14.9; Sergeev, Sharma and Shukla, 2012, p. 332 and 333, pl. 26, fig. 9.


Description.—Spheroidal, solitary, single-walled vesicles 35–40 μm in diameter; walls are translucent, hyaline to fine- grained, <1 μm thick and have a smooth surface texture.


Material examined.—Nine well-preserved specimens.


Occurrence.—Widely distributed in Proterozoic and Paleozoic rocks.


Leiosphaeridia tenuissima Eisenack, 1958 Figure 13.9


Leiosphaeridia tenuissima Eisenack, 1958, pl. 1, fig. 2; Yankauskas, 1989, p. 81, pl. 9, figs. 12, 13; Butterfield in Butterfield, Knoll and Swett, 1994, p. 42, fig. 16I (for complete synonymy, see Yankauskas, 1989).


Description.—Spheroidal, solitary, single-walled vesicles


70–80 μm in diameter; walls are translucent, hyaline to fine-grained, about 2-μm thick, and have a smooth surface texture.


Material examined.—Four well-preserved specimens.


Occurrence.—Widely distributed in Proterozoic and Paleozoic sedimentary rocks.


Remarks.—Species of Leiosphaeridia are identified following a formal scheme based on envelope diameter and wall thickness (see Yankauskas, 1989, p. 24 and 25). Although some speci- mens of Leiosphaeridia may be empty envelopes that originally enclosed cyanobacterial colonies, the great majority are remains of eukaryotic unicellular phytoplankton.


Genus Myxococcoides Schopf, 1968 Type species.—Myxococcoides minor Schopf, 1968.


Myxococcoides inornata Schopf, 1968 Figure 14.10


Myxococcoides inornata Schopf, 1968, p. 676 and 677, pl. 84, fig. 7; Sergeev, Knoll, and Petrov, 1997, p. 234, figs. 18B, 18G; Sergeev, 2001, p. 444, fig. 10.11; Sergeev and Lee Seong-Joo, 2004, p. 17, pl. 3, fig. 12; Sergeev, 2006, p. 226, pl. 15, figs. 6, 7, pl. 21, fig. 1, pl. 29, fig. 18; Sergeev and Schopf, 2010, p. 393, fig. 12.3, 12.4; Schopf, Kydryavtsev and Sergeev, 2010a, fig. 5.1–5.4; Sergeev, Sharma, and Shukla, 2012, pl. 5, fig. 8, pl. 6, fig. 9.


Description.—Spheroidal cells, solitary or occurring in colonies composed of few to tens of individuals embedded in a diffuse commonly well-defined organic matrix. Cell diameters range from 15 to 20 μm; colony size is 50–70 × 100–120 μm. The single-layered cell walls are typically translucent, fine- or medium-grained, 0.5–1.0 μm thick. Some cells contain an opaque spheroidal inclusion 1–2 μm in diameter that appears to be attached to the inner surface of the cell wall.


Material examined.—Tens of well-preserved cells in several colonies.


Figure 14. Optical photomicrographs (1, 3, 4, 7, 9–12) and confocal laser scanning micrographs (2, 5, 6, 8) of Chulaktau Formation coccoidal colonial and unicellular chert- and apatite-permineralized organic-walled microfossils. (1, 2, 4, 5) Cymatiosphaera sp.: (1, 2) 4681-1026 (273), specimen location point (p.) 17, England Finder Slide (EFS) F60[3], GINPC 1289. Although here referred to Cymatiosphaera, the numerous hemispherical cuspate structures situated on the inner wall of this specimen may be sites of apatite nucleation (cf. Fig. 3.16 and 3.17), an interpretation consistent with the resemblance of the elongate linear arcuate band that extends across the upper part of the spheroid interior to mineralic structures that are a result of void-filling crystallization. If not Cymatiosphaera, this specimen is probably an apatite-infilled leiosphaerid. (4, 5) 4681-367 (100), p. 5b, EFS P50[3], GINPC 1290. The upper hemisphere of this specimen of Cymatiosphaera was ground away during preparation of the fossil-bearing petrographic thin section resulting in exposure of the ring-like circularity of the medial plane of the specimen at the upper surface of the section. (3, 6) Vandalosphaeridium koksuicum Sergeev and Schopf, 2010, 4681-1026 (273), p. 130, EFS Q27[0], GINPC 1291. (7–9) Synodophycus sp.: (7, 8) 4681-367 (100), p. 5a, EFS P50[3], GINPC 1292; 9, 4681-413 (238), p. 10, U40[1], GINPC 214. (10) Myxococcoides inornata Schopf, 1968, 4681-364 (192), p. 10a, EFS P48[1], GINPC 1293. (11) Myxococcoides minor Schopf, 1968, 4681-359 (15), p. 3, EFS G31[0], GINPC 1294. (12) Eoaphanocapsa molle Sergeev, 1989, 4681-368 (98), p. 7, EFS INPC 209.


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