400
Journal of Paleontology 91(3):393–406
Holotype.—HUPC# 64453, upper Tonian (~742±6 Ma), Kwagunt Formation, Chuar Group, Arizona.
Material.—N = 10; GP/5T 2529 G, H, J, K; 2531 C; 2532 A, C, D, F, G.
Diagnosis.—Specimens of the genus Cycliocyrillium in which test walls curve orally toward each other and form a a narrow, slightly thickened collar or proceed parallel as a short uncurved neck, not exceeding one-tenth total specimen length, which terminates at the apertural edge.
Description.—Specimens from the Urucum Formation have pyriform tests (L = 53–113 µm, x = 78 µm; σ = 27 µm; W = 40–84 µm, x = 58 µm, σ = 19 µm) with a short neck (NL = 2–10 µm, x = 6 µm, σ = 3 µm), terminating in a circular aperture (AD = 12–34 µm, x = 21 µm, σ = 10 µm). Aspect ratios (L/W) range from 1.2 to 1.5 (x = 1.3; σ = 0.09). Walls carbonaceous or siliceous, of uniform thickness (WT = 4–7 µm, x = 5.3 µm, σ = 1.3 µm).
Remarks.—All Urucum specimens of C. torquata exhibit short necks rather than collars.
Genus Palaeoamphora Morais, Fairchild, and Lahr, new genus
Type species.—Palaeoamphora urucumense n. gen. n. sp., by monotypy. Diagnosis.—As for type species, by monotypy.
Etymology.—From palaeo, Greek, ancient; and amphora, Latin, a type of antique Greek vase; with reference to the antiquity and shape of the microfossil.
Remarks.—The funnel-like neck clearly distinguishes Palaeoamphora n. gen. from other taxa having long or short uncurved necks (e.g., Limeta lageniformis n. gen. n. sp. and Cyclocyrillium torquata Porter et al., 2003, respectively).
Palaeoamphora urucumense Morais, Fairchild, and Lahr, new species
Figures 5.3–5.5, 6.4–6.6 2003 Unnamed form Porter et al., p. 423, fig. 17.1–17.3.
Type material.—N = 6; Holotype, GP/5T-2534 F (Fig. 6.6). Paratypes (Fig. 6.4, 6.5), GP/5T: 2433 A; 2534 B; 2536 A, B; GP/5T: 2540 A, from the Neoproterozoic Urucum Formation, Jacadigo Group, Corumbá, Brazil (Repository: LPS, IGc-USP).
Diagnosis.—VSMs having a pyriform test with a funnel-like neck comprising up to one-sixth the total length of the specimen.
Description.—Total test length (L) = 90–135 µm; x = 115 µm;
σ = 17 µm; W = 60–109 µm, x = 83 µm, σ = 18 µm. Circular aperture (external aperture diameter, AD = 37–66 µm, x = 52 µm; σ = 12 µm) at the terminus of a flaring, funnel-like neck comprising no more than one-sixth total specimen length
Etymology.—After the Urucum Formation, in which it was found.
Remarks.—Porter et al. (2003, fig. 17.1–17.3) previously dis- tinguished an “unnamed form” in the Chuar Group, consisting of siliceous casts of three incomplete specimens with partially preserved funnel-like necks. The discovery of seven similar, organically preserved forms with complete necks in the Urucum Formation justifies the erection of this taxon to include all these specimens.
Genus Limeta Morais, Fairchild, and Lahr, new genus
Type species.—Limeta lageniformis n. gen. n. sp., by monotypy. Diagnosis.—As for type species, by monotypy.
Figure 7. Comparison of modern testate amoebae (1–4) and VSMs from the Neoproterozoic Urucum Formation (Jacadigo Group, Corumbá, Brazil) (5, 6). (1, 2) Longitudinal (1) and transverse (2) views of modern Difflugia (images: D.J.G. Lahr); (3, 4) longitudinal (3) and transverse (4) views of modern Padaungiella (images, D.J.G. Lahr); (5, 6) longitudinal (5) and transverse (6) views of paratypes of Limeta lageniformis n. gen. n. sp. with shape similar to Difflugia (GP/5T-2536 C, B, respectively). Scale bars = 20 µm(1, 2), 37.5 µm(3), 17.5 µm(4), 50 µm(5), or 20 µm(6).
(NL = 11–19 µm, x = 15 µm; σ = 3.2 µm). Body length (L minus NL = BL), 78–124 µm(x = 99 µm; σ = 17.5 µm). Total specimen aspect ratios (L/W) 1.2–1.7 (x = 1.4; σ = 0.17); body aspect ratios (BL/W) 1.1–1.4 (x = 1.22 µm; σ = 0.13 µm). Walls carbonaceous, of uniform thickness (WT = 5–6 µm; x = 5.3 µm; σ = 0.57 µm).
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