Conotheca spp.

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 : 445

Conotheca spp.

Fig. 28 .

Material.—Several phosphatised opercula with cardinal processes, including SMNH X 4630–4632, from sample K1-3B; uppermost Emyaksin Formation, Malaya Kuonamka; Calodiscus -Erbiella Zone, lower Botoman Stage. One operculum, SMNH X 4633, from sample 7/31.5; Emyaksin Formation, Bol’shaya Kuonamka; correlated with the Delgadella anabara Zone, Atdabanian Stage.

Remarks.—Circular opercula from sample K1-3B with two prominent cardinal processes, nearly perpendicular to the surface of the operculum ( Fig. 28A–C ). The processes diverge at ca. 30º. The inner surface has a smooth distal ridge at the margin, low rounded polygonal pattern in the middle and faint radial striation laterally. The margin thins out gradually. Conchs with circular cross-section are not found in sample K1-3B, but occur in the coeval sample 7/70 from Bol’shaya Kuonamka.

The operculum from sample 7/31.5 has weakly developed cardinal processes and radially oriented lateral folds of the circular distal ridge ( Fig. 28D ). The ridge slopes abruptly towards the margin of the operculum. Radial folds developed laterally on the distal ridge are reminiscent of those described as tubular clavicles ( Malinky and Skovsted 2004) in Conotheca australiensis Bengtson in Bengtson et al., 1990, of which the interior surface morphology is otherwise different. Several straight fragments of conchs with circular cross-section ( Fig. 27H ) co-occur with the operculum in sample 7/31.5.

Figures

Fig. 28. Hyolith opercula Conotheca spp. from lower Cambrian Emyaksin Formation, Malaya Kuonamka River and Bol’shaya Kuonamka River, Anabar Uplift, Siberia. A–C. Opercula with long processes, sample K1-3B. A. SMNH X 4630; oblique dorsal (A1), inner (A2), and lateral (A3) views. B. SMNH X 4631; dorsal (B1), inner (B2), and lateral (B3) views. C. SMNH X 4632; outer view. D. Operculum without processes, SMNH X 4633, sample 7/31.5; dorsal (D1) and inner (D2) views. Scale bar 600 μm, except A1, 300 μm.

Fig. 27. Hyolith conchs from lower Cambrian Emyaksin Formation, Bol’shaya Kuonamka River and basal Kuonamka Formation, Malaya Kuonamka River, Anabar Uplift, Siberia. A–E, H. Conotheca cf. C. mammilata Missarzhevsky in Rozanov et al., 1969. A. SMNH X 4623, sample 7/29; longitudinal view on presumably dorsal side. B. SMNH X 4621, sample 7/27.5; longitudinal view on presumably dorsal side. C. SMNH X 4622, sample 7/27.5; longitudinal view. D. SMNH X 4663, sample 7/30; D1, transversal view from the apertural end; D2, longitudinal view. E. SMNH X 4620, sample 3/65; lateral (E1) and dorsal (E2) views. H. SMNH X 4624, sample 7/31.5; longitudinal view. F. Conotheca circumflexa Missarzhevsky in Rozanov et al., 1969, SMNH X 4629; F1, oblique longitudinal view showing transversal section; F2, longitudinal view. G, J. Linevitus? minutus Missarzhevsky in Rozanov and Missarzhevsky, 1966. G. SMNH X 4657, sample 7/31.5; lateral (G1), dorsal (G2), and apertural (G3) views. J. SMNH X 4658, sample 7/70; ventral side with growth increments. →