Cupitheca sp.

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 : 406

Cupitheca sp.

Fig. 44 .

Material.—Several hundred phosphatised conchs and calcium phosphatic internal moulds, including figured SMNH X11164–11172, from samples 19/5.5,19/8.5, 19/10.25, 19/11.75, 19/12.75, 19/25.5, 19/26.75, 19/29, 19/33, 20/1B, Erkeket Formation, Khorbusuonka River, Botoman and Toyonian stages correlated with the Cambrian Stage 4) and sample 21/51, Tyuser Formation, Delgadella anabara – Nevadella Zone, Atdabanian stage (correlated with the Cambrian Stage 3). Siberia, Russia.

Remarks.—Represented by phosphatised fragments of conchs gently curved in sagittal plane, with circular cross-section and straight aperture. Apical end of the fragments with a hemispherical, apically convex septum. Wall carries irregular thin growth lines and circumferentially running densely arranged fibers in the inner layer. The outer layer and surface of the septum has a porous structure. Deeper portion of the septum preserved as parallel columns perpendicularly oriented to the outer and inner surfaces. The columns are phosphatic infills of the porous channels through the septum. Apices of the conchs are detached and few co-occurring fragments can herein be interpreted as initial parts broken off along the septal margin. They are goblet-shaped, with an extended tip having a blunt termination, abruptly expanding towards a circular aperture.

Opercula ( Fig. 45 ) are found associated with the conchs, but they cannot be unequivocally interpreted as belonging to the same species. They are circular with flat, slightly undulating outer side carrying concentric growth lines. Bilaterally symmetrical structures on the inner side represent elevated lateral undulating ridges with radial folds. Ridges dip steeply towards the margin of the operculum and slope gently towards the initial part. The initial part is centrally situated in the operculum and represents an elevated cone on the exterior surface opposed by a deep pit on the interior. There is a sinus between the elevated dorsal parts of the ridges, on the dorsal side of the operculum. The ridges level off towards the ventral one-third part of the operculum, where the ventral sector is gently convex on the interior.

Forms described under such names as Cupitheca Duan in Xing et al., 1984, and Actinotheca Xiao and Zhou, 1984 , recovered as conch fragments with circular to broadly oval cross-section and a hemispherical, apically convex terminal septum can be interpreted as a mode of preservation in a polyphyletic group of orthothecid hyoliths with a septum in the apical part and a circular cross-section. A similar mode of preservation occurs, e.g. in Majatheca tumefacta Missarzhevsky in Rozanov et al., 1969, with a broken off apical part ( Kouchinsky et al. 2015a: fig. 22B 3).

Figures

Fig. 44. Hyolith conchs Cupitheca sp., from the lower Cambrian Erkeket Formation, Khorbusuonka River, Siberia, Russia; samples 19/12.75 (E–I) and 19/33 (A–D). A, B, E–I. Phosphatised conchs, SMNH X11164–11170, respectively.A1, B3, lateral view; A2, close-ups of the apical end; B2, dorsal view. B1, enlarged apical end showing septum. E–H, fragments of conch with septum. I, probable operculum of the same species within apertural end of conch. C, D. Apical ends of conch, presumably of the same species, with initial parts preserved, SMNH X11171 and 11172, respectively. D1, oblique apertural view; D2, lateral view. Scale bar: 500 µm (A1, B2, B3, C), 250 µm (D, H, I), and 125 µm (A2, B1, E–G).

Fig. 45.Hyolith opercula, presumably Cupitheca sp. (see Fig. 44), from the lower Cambrian Erkeket Formation, Khorbusuonka River, Siberia,Russia; sample 19/12.75. A–E. Phosphatised opercula, SMNH X11173–11177, respectively.A1, C1, outer surface; A2, lateral view; C2, oblique dorsal view; D1, inner surface; D2, oblique lateral view. Scale bar 250 µm.