Lapworthella tortuosa 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 : 375

Lapworthella tortuosa Missarzhevsky in Rozanov and Missarzhevsky, 1966

Fig. 23G–I, L–N .

Material.—Several tens of sclerites from samples 11/18.7, 11/19.5, 11/21.6, Khorbusuonka River and several sclerites, including illustrated SMNH X11026–11031, from sample 21/22.7, Lena River. Siberia, Russia; Dokidocyathus regularis Zone, Tommotian stage (correlated with the upper part of Cambrian Stage 2).

Description.—Elongated conical sclerites, up to 1 mm long with rounded isometrical, subrectangular or more extended oval aperture, up to 0.5 mm wide. Almost straight or gently curved in one plane, sometimes irregularly curved at the pointed tip. External ornamentation consists of distinct transversal denticulated ridges bearing growth lines. Distance between ridges ca. 100 µm. Rings between ridges are concave with numerous tubercles and are wider than smooth surface of the ridges.

Remarks.—Forms with isometrical and flattened cross-sections are known from the same samples. Irregularly curved tip in a single sclerite attributed to the same species has not been previously reported.

Stratigraphic and geographic range.—Tommotian stage, Siberian Platform.

Lapworthella dentata Missarzhevsky in Rozanov et al., 1969

Fig. 23O–Q .

Material.—Single sclerite, SMNH X11032, from sample 19/31.75and several tens of sclerites,including figured SMNH X11033 and 11034, from sample 20/5B, Khorbusuonka River, Siberia, Russia. Toyonian stage (correlated with Cambrian Stage 4).

Description.—Pyramidal, slightly curved sclerites, up to 1 mm long, with oval or subrectangular aperture, up to 0.5 mm wide. External ornamentation consists of distinct transversal ridges bearing short denticles. The density of denticles is 35–50 per mm. Distance between ridges 50– 100 µm. Rings between ridges are concave with circumferential growth lines.

Stratigraphic and geographic range. —Cambrian Series 2, Siberian Platform. Occurrence beyond the Siberian Platform depending on synonymy with Lapworthella schodackensis ( Lochman, 1956) from Laurentia ( Landing, 1984) and Lapworthella cornu ( Wiman, 1903) from Baltica and Avalonia (see discussion by Devaere and Skovsted 2017).

Figures

Fig. 23. Tommotiid Lapworthella Cobbold, 1921 from the Cambrian Erkeket Formation, Khorbusuonka River (A–D, F–L, O–Q) and Tyuser Formation, lower reaches of the Lena River (E, M, N), Siberia, Russia; samples 11/18.7 (G, L), 11/21.6 (H, I), 19/1.5 (D), 19/5.5 (F, J, K), 19/31.75 (Q), 20/1B (A–C), 20/5B (O, P), 21/22.7 (M, N), 21/112 (E). A–F, J, K. Lapworthella lucida Meshkova, 1969 sclerites, SMNH X11018–11025, respectively. G–I, L–N. Lapworthella tortuosa Missarzhevsky in Rozanov and Missarzhevsky, 1966 sclerites, SMNH X11026–11031, respectively. O–Q. Lapworthella dentata Missarzhevsky in Rozanov et al., 1969 sclerites, SMNH X11032–11034, respectively. Scale bar 250 µm.