Egdetheca aldanica Missarzhevsky

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 : 403

Egdetheca aldanica Missarzhevsky in Rozanov et al., 1969

Fig. 40I–K .

Material.—Over 20 calcium phosphatic internal moulds, including figured SMNH X11144–11146, from samples 11/2B, 11/16.05, 11/16.1, 11/16.5, basal Erkeket Formation, Khorbusuonka River, and sample 21/21, Tyuser Formation, Lena River; Siberia, Russia. Dokidocyathus regularis Zone, Tommotian stage (upper part of Cambrian Stage 2).

Remarks.—Conchs slowly expanding and slightly curved in sagittal plane, with a semi-oval or rounded trapezoidal cross-section. Initial part extended concave on the ventral side and slightly bulbous at the end. The surface of the internal mould is usually covered with ca. 10 µm low tubercles, which in combination with the general morphology of the mould is diagnostic for the species.

Stratigraphic and geographic range.— Nochoroicyathus sunnaginicus and Dokidocyathus regularis zones, Tommotian stage (correlated with the upper part of Cambrian Stage 2), Siberian Platform, Russia.

A 4, pertural view; A 1, A 2, enlargements of the apical part and aperture. B. Shell sealed with operculum (contact between the edge of the aperture and dorsal margin of the operculum arrowed). B 1,oblique apertural view; B 2, lateral view showing ventral sinus of the aperture (arrows). C. Shell showing septum at the apical end (C 1, close-up). D. Shell preserved as inner phosphatic coating including that of the apical septum; D 1, lateral view; D 2, apertural view. E. Shell with apertural sinus; E 2, ventral side arrowed; E 1, enlargement of the apical end; E 3, ventral side. Scale bar: 500 µm (A 3, A 4, B 2, C 2, D, and E 2) and 165 µm (A 1, A 2, B 1, C 1, E 1, and E 3).

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).