Conotheca cf. longiconica ( Qian, 1978 )

Kouchinsky, Artem, Alexander, Ruaridh, Bengtson, Stefan, Bowyer, Fred, Clausen, Sébastien, Holmer, Lars E., Kolesnikov, Kirill A., Korovnikov, Igor V., Pavlov, Vladimir, Skovsted, Christian B., Ushatinskaya, Galina, Wood, Rachel & Zhuravlev, Andrey Y., 2022, Early-middle Cambrian stratigraphy and faunas from northern Siberia, Acta Palaeontologica Polonica 67 (2), pp. 341-464 : 401

Conotheca cf. longiconica ( Qian, 1978)

Fig. 40E, F .

Material.—Over 20 phosphatised conchs, including figured SMNH X11142 and 11143, from sample 19/25.5, Erkeket Formation, Khorbusuonka River, Toyonian stage (correlated with the Cambrian Stage 4) and samples 21/46.1, 21/51, 21/52, 21/54, Tyuser Formation, Lena River, Delgadella anabara – Nevadella Zone, Atdabanian stage (correlated with the Cambrian Stage 3). Siberia, Russia.

Description.—Conch gently curved in sagittal plane, with circular cross-section and straight aperture. Apical angle ca. 10°. Juvenile conch rounded blunt, not clearly separated. Wall porous consisting of a network of fibers, similarly to other hyoliths.

Remarks.—This form is more curved and slimmer than the holotype of C. mammilata . It occurs in the Cambrian Stages 2 and 3 of the Siberian Platform. Similar conchs are illustrated by Kouchinsky et al. (2015a: figs. 25E–G, 27E; 2017: fig. 52). Qian and Bengtson (1989) synonymised Circotheca longiconica Qian, 1978 , with Conotheca subcurvata ( Yu, 1974) . We support herein placement within Conotheca , but find difference between these two species. Conotheca longiconica ( Qian, 1978) has a conch regularly curved in a single plane, whereas Conotheca subcurvata shows irregular curvature (see Luo et al. 1984: pl. 7: 8).

Figures

Fig. 40. Hyolith conchs from the lower Cambrian Erkeket Formation, Khorbusuonka River (A–D, G, H, K–N) and Tyuser Formation, lower reaches of the Lena River (E, F, I, J), Siberia, Russia; samples 11/16.05 (K), 11/16.1 (A), 11/16.5 (B, C), 11/2B (D), 19/4.25 (H), 19/11.75 (L), 19/12.75 (M, N), 19/14.25 (G), 21/21 (I, J), and 21/51 (E, F). A, B. Conotheca mammilata Missarzhevsky in Rozanov et al., 1969, phosphatised conchs, SMNH X11136 and 11137, respectively. C, D. Conotheca mammilata Missarzhevsky in Rozanov et al., 1969, phosphatised conchs with initial part preserved, SMNH X11138 and 11139, respectively. E, F. Conotheca cf. longiconica (Qian, 1978), phosphatised conchs, SMNH X11142 and 11143, respectively. G, H. Conotheca circumflexa Missarzhevsky in Rozanov et al., 1969, phosphatised conchs, SMNH X11140 and 11141, respectively.H2, close-up showing transversal fibers in the wall. I–K. Egdetheca aldanica Missarzhevsky in Rozanov et al., 1969, calcium phosphatic internal moulds, SMNH X11144–11146, respectively. K1, lateral view; K2, apical view.L–N. Orthothecida sp. indet., calcium phosphatic internal moulds, SMNH X11147–11149, respectively. M1, lateral view; M2, dorsal view. Scale bar: 1 mm (A), 500 µm (B–D, G–K), 250 µm (E, F, L–N), and 50 µm (H2).