Khairkhania cf. evoluta Zhegallo, 1982

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 : 355

Khairkhania cf. evoluta Zhegallo in Voronin et al., 1982

Fig. 25A–C .

Material.—17 internal moulds, including figured SMNH Mo182291–182293, from samples 1/29.5 (section 1, Fig. 4 ), K1a/82 (section 2, Fig. 1), K2/38A, K2/43, and K2/46 (section 3, Fig. 3), from the Medvezhya Formation (SOM 1), western Anabar Uplift, Siberian Platform, Russia. Correlated with the upper Fortunian Stage.

Description.—Planispiral, slowly expanding cyrtoconic shells coiled up to 3/4 of a revolution, with rounded protoconch indistinctly separated from the rest of the shell, represented by smooth internal moulds. Cross-section broadly oval, nearly circular.

Remarks.— Khairkhania evoluta was first described from the upper Fortunian–Cambrian Stage 2 equivalent beds of western Mongolia (Voronin et al. 1982). One morphologically similar fossil, albeit with a hyolith-type microstructure of the wall, was described from the Zhongyicun Member of the Meishucunian Stage of South China (Fortunian Stage; Feng et al. 2001b). Multiple columns representing casts of canals orthogonally oriented in the shell wall were described from the probable kindred species Khairkhania rotata and from such generally similar but dextrally and sinistrally coiled forms as Philoxenella spiralis Vostokova, 1962 , and Barskovia hemisymmetrica Golubev, 1976 , respectively (Parkhaev 2006, 2007b; see below). The columns are also similar to those present in the tubes and opercula of hyoliths (Kouchinsky 2000b; Kouchinsky et al. 2015a). The polygonal impressions sometimes preserved on the apex of Aldanella spp. internal moulds ( Figs. 18B 3, 20A 3, 23H 1) have never been reported from Barskovia , Nomgoliella , Philoxenella , or Khairkhania . This lack of apical polygonal impressions further corroborates the taxonomic distinctiveness of the latter four genera among other coeval mollusc-like fossils.

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).

Fig. 4. The δ13Ccurve for Kotuj River section 1and sampled horizons with fossiliferous samples (arrows with numbers). Shift in stratigraphic column carb at Nemakit-Daldyn–Medvezhya formations contact indicates position of sequence boundary. Stratigraphic ranges and first appearances of fossils (see SOM 1): 2, Oelandiella korobkovi; 3, Securiconus cf. simus; 4, Bemella jacutica?; 8, Anabarella plana; 9, Watsonella crosbyi; 10, Pseudoyangtzespira selindeica; 11, Aldanella crassa; 13, Aldanella attleborensis; 15, Philoxenella spiralis; 16, Barskovia hemisymmetrica; 18, Khairkhania cf. evoluta; 19, Ceratoconus striatus; 21, Salanyella cf. costulata; 23, Purella cristata; 25, Yunnanopleura sp.; 26, Obscurania auriculata; 29, Protoconus cf. crestatus; 32, Siphogonuchites triangularis; 34, Lopochites sp.; 37, first appearance of Halkieria sp.; 39, first appearance of Chancelloria sp.; 40, Tianzhushanella sp.; 42, Khetatheca cotuiensis; 46, Turcutheca sp.; 48, Orthothecid operculum type A; 52, Fomitchella infundibuliformis; 57, Hyolithellus sp.; 62, Selindeochrea missarzhevskyi; 63, Selindeochrea ternaria; 64, Anabarites trisulcatus; 67, Anabarites kelleri; 68, Anabarites biplicatus; 71, Anabarites hexasulcatus; 74, Tiksitheca licis; 75, Cambrotubulus decurvatus; 76, Platysolenites antiquissimus; 77, Blastulospongia sp.

Fig. 18. Mollusc Aldanella crassa Missarzhevsky in Rozanov et al., 1969, internal moulds, from early Cambrian Medvezhya Formation, Kotuj River, western Anabar Uplift, Siberia, Russia; samples 1/50 (A, B, D–F), section 1; samples K2/13 (C) and 3/6.5 (G), section 3. A–G. SMNH Mo182246– 182252, respectively. A1, B1, C2, D, E1, F, G1, adapical side; E2, oblique adapical view; A3, oblique umbilical side; A2, B3, C1, G2, apertural views; B2, close-up of apex with polygonal relief. Scale bar 200 μm (B2), 500 μm (A, B1, B3), and 1 mm (C–G).