Selindeochrea tricarinata

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 : 413

Selindeochrea tricarinata (Missarzhevsky in Rozanov et al., 1969)

Fig. 69 .

Material.— Over 50 specimens, including figured SMNH X3412 , 5978 , 5980–5982 , from samples K2/21, K2/25, K2/50, 3/12, and 3/12.2 (section 3, Fig. 3), Medvezhya Formation , western Anabar Uplift , Siberian Platform , Russia. Correlated with the upper Fortunian and lowermost Cambrian Stage 2 .

Description.—Slowly expanding slightly curved tubes with tri-lobate cross-sections, slightly twisted clockwise (from apex to the aperture, in the direction of growth). Grooves (depressions) between extended lobes are wide and shallow with flattened middle part. There is a narrow median ridge on the flattened depressions between the lobes (as replicated by internal moulds). In the flattened depressions, the growth lines are arched and point at an acute angle towards the aperture. In preserved thecae, the lobes are extended distally by prominent keels. The keels undulate, with folds running towards the aperture at ca. 45°. The lobes of the internal moulds are rounded or somewhat swollen and almost straight.

Stratigraphic and geographic range.— Upper Fortunian– lower part of Cambrian Stage 2 of the Siberian Platform.

Figures

Fig. 69. Anabaritid Selindeochrea tricarinata (Missarzhevsky in Rozanov et al., 1969), from early Cambrian Medvezhya Formation, western Anabar Uplift, Siberia, Russia; samples K2/25 (A, C), 3/12.2 (B, D), and 3/12 (E, F), section 3. A. SMNH X3412-part (see also Kouchinsky et al. 2009: fig. 48C); A1, phosphatic internal mould with external phosphatic coating of longitudinal lobes and their distal extensions, keels; A2, cross-section enlarged. B, F. SMNH X5978, 5982, respectively; phosphatic external moulds with longitudinal keels; B, F1, lateral; F2, oblique views. C. SMNH X3412- counterpart (see also Kouchinsky and Bengtson 2002: fig. 9A and Kouchinsky et al. 2009: fig. 48D), cast of the outer surface. D, E. SMNH X5980 and 5981, respectively; phosphatic internal moulds; D1, E2, transverse; D2, E1, lateral views. Scale bar 250 μm (A2) and 500 μm (A1, B–F).