Khairkhania cf. rotata Missarzhevsky, 1981

Kouchinsky, Artem, Bengtson, Stefan, Landing, Ed, Steiner, Michael, Vendrasco, Michael & Ziegler, Karen, 2017, Terreneuvian stratigraphy and faunas from the Anabar Uplift, Siberia, Acta Palaeontologica Polonica 62 (2), pp. 311-440 : 353-355

Khairkhania cf. rotata Missarzhevsky, 1981

Fig. 25D .

Material.—Single phosphatized internal mould SMNH Mo182294 and seven fragments of internal moulds of presumably the same species from sample 3/0 (section 3, Fig. 3), basal Medvezhya Formation (see SOM 1), western Anabar Uplift, Siberian Platform, Russia. Correlated with upper Fortunian Stage.

Description.—Planispiral shell, relatively tightly coiled through ca. 1 revolution, with blunt rounded apex and indistinctly separated protoconch. Cross-section broadly oval.

Remarks.— Khairkhania rotata from western Mongolia and forms of this species described by Parkhaev (2006, 2007b, 2008) from the northwestern flanks of the Anabar Uplift are generally similar but smaller (ca. 75% in size) than the material illustrated herein as Khairkhania cf. rotata ( Fig.

25D). Khairkhania sp. from the same sample are either fragmentary or open coiled with up to 1/2 revolution ( Fig. 25E, F ). They may represent a different species, morphological variants, or younger growth stages of the same species. Khairkhania cf. evoluta (see below) is represented by high, cyrtoconic, relatively more laterally compressed internal moulds with smaller protoconchs.

Figures

Fig. 25. Molluscs? Khairkhania Missarzhevsky, 1981, from early Cambrian Medvezhya Formation, Kotuj River, western Anabar Uplift, Siberia, Russia; samples K1a/82 (A, B), section 2; 1/29.5 (C), section 1; and 3/0 (D–F), section 3. A–C. Khairkhania cf. evoluta Zhegallo in Voronin et al., 1982, internal moulds with partly phosphatized shell, SMNH Mo182291–182293, respectively. D. Khairkhania cf. rotata Missarzhevsky, 1981, internal mould, SMNH Mo182294. E, F. Khairkhania sp., internal moulds with partly phosphatized shell, SMNH Mo182295, 182296, respectively.A, B1–F1, lateral; B2, C2, E2, subapical; D2, F2, apertural views. Scale bar 500 μm (A–C), 1 mm (D–F).