Figurina, Parkhaev, 2001

Kouchinsky, Artem, Bengtson, Stefan, Clausen, Sébastien & Vendrasco, Michael J., 2015, An early Cambrian fauna of skeletal fossils from the Emyaksin Formation, northern Siberia, Acta Palaeontologica Polonica 60 (2), pp. 421-512 : 427

Figurina cf. F. nana ( Zhou and Xiao, 1984)

Fig. 8 .

Material.—Two phosphatised internal moulds, SMNH Mo167659 and 167660 from sample 7/70. Uppermost Emyaksin Formation, Bol’shaya Kuonamka River; CalodiscusErbiella Zone, lower Botoman Stage.

Description.—Low, slightly cyrtoconic, laterally somewhat compressed shell, 0.8–0.9 mm in width and height and 1.7 mm long, with rounded apex displaced towards the apertural margin and indistinct protoconch. The inner shell surface (as reflected by internal moulds) has faint transversal folds. Sub-apical surface is very short. Aperture oval, a little flared, with subapical train.

Remarks.—Internal mould is covered with shallow pits, 10 μm in diameter ( Fig. 8A 4 ). The fossils have diagnostic features of Figurina Parkhaev in Gravestock et al. 2001. Compared to the type species, F. figurina Parkhaev in Gravestock et al. 2001 (Series 2, Australia), F. capitata Parkhaev in Gravestock et al. 2001 (Series 2, Australia), F. groenlandica Skovsted, 2004 (Stage 4, Laurentia), and F. nana ( Zhou and Xiao, 1984) (Series 2, North China and Australia), the fossils are most similar to F. nana (see Gravestock et al. 2001: pl. 35: 7), but one of the specimens herein ( Fig. 8B ) appears wider. Figurina cf. F. nana are also similar to internal moulds of juveniles of Mackinnonia anabarica (see below, Figs. 9C , 11C ), but are twice as big and have wider and less curved apex.

Genus Mackinnonia Runnegar in Bengtson et al., 1990

Type species: Mackinnonia davidi Runnegar in Bengtson et al., 1990; Abadiella huoi Zone , lower Cambrian; Horse Gully section, Yorke Peninsula, Australia.

Figures

Fig. 8. Helcionellid mollusc Figurina cf. F. nana (Zhou and Xiao, 1984) internal moulds from lower Cambrian Emyaksin Formation, Bol’shaya Kuonamka River, Anabar Uplift, Siberia; sample 7/70. A. SMNH Mo 167659; upper (A1), lateral (A2), and sub-apical (A3) views; A4, close-up of A1, pits on the surface of internal mould. B. SMNH Mo 167660; upper (B1), sub-apical (B2), lateral (B3, B4) views. Scale bar 600 μm, except A4, 30 μm.

Fig. 4. Helcionellid mollusc Bemella? sp. internal moulds from lower Cambrian Emyaksin Formation, Bol’shaya Kuonamka River,Anabar Uplift, Siberia; sample 7/36.7. A. SMNH Mo 167650; lateral (A1), apertural (A2), and sub-apical (A3) views. B. SMNH Mo 167651; lateral (B1) and upper (B2) views. C. SMNH Mo 167652; apertural (C1), lateral (C2), and sub-apical (C3) views. D. SMNH Mo 167653; D1, close-up of apertural margin in D3; upper (D2) and lateral (D3) views. Scale bar 1200 μm, except D1, 300 μm.

Fig. 9. Helcionellid mollusc Mackinnonia anabarica Parkhaev, 2005 internal moulds from lower Cambrian Emyaksin Formation, Bol’shaya Kuonamka River, Anabar Uplift, Siberia; sample 7/70. A. SMNH Mo 167662; lateral (A 1), sub-apical (A 2), and upper (A 3) views. B. SMNH Mo 167663; lateral (B 1), sub-apical (B 2), upper (B 3), and supra-apical (B 4) views. C. SMNH Mo 160419; supra-apical (C 1), lateral (C 2), sub-apical (C 3), and upper (C 4) views. D. SMNH Mo 167664; supra-apical (D ), upper (D ), lateral (D ), and sub-apical (D ) views. Scale bar 600 μm.

Fig. 11. Helcionellid mollusc Mackinnonia anabarica Parkhaev, 2005 internal moulds from lower Cambrian Emyaksin Formation, Bol’shaya Kuonamka River, Anabar Uplift, Siberia; sample 7/70. A. SMNH Mo 160420; A1, lateral view; A2, close-up of A1, microtexture on the surface of internal mould, detailed. B. SMNH Mo 167665 (see also Fig. 10); lateral view. C. SMNH Mo 160419 (see also Fig. 9C); C1, lateral view; C2, close-up of C1, polygons on the surface of internal mould. Scale bar: 300 μm, except A2, 120 μm; C2, 60 μm.