Abnormisella 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 : 439

Abnormisella sp.

Fig. 71K, L .

Material.—Single spicules, SMNH Sp11416, from sample 11/18.7, lower Erkeket Formation, Khorbusuonka River and SMNH Sp11415, from sample 6/0.3, Emyaksin Formation, Remarks.—Without defining a holotype, Fedorov and Pereladov (1987) attributed a number of co-occurring pentactines and stauractines from the middle Cambrian Kuonamka Formation to Abnormisella insperata Fedorov in Fedorov and Pereladov, 1987, including pentactines with a long axial ray and four paratangential rays diverging at 90–180° with respect to the axial ray. Subsequently, Peel (2019) selected a lectotype and emended diagnosis of the genus and its type species. The emended diagnosis included only pentactines with inclined axial ray, thus appearing bilaterally symmetrical. Forms found in Cambrian Stage 4–Guzhangian Stage of North Greenland attributed by Peel (2019) to A. insperata have an acanthose axial ray of a greater diameter than those of paratangential rays arranged in two pairs having different cross-sectional diameters, that is not the case in the spicules described herein and by Kouchinsky et al. (2015a). Peel (2019) attributed Speciosuspongia wangcunensis Chen and Dong, 2008 , from the Drumian (middle Cambrian) of South China to the same genus, but they have thicker and swollen acanthose axial rays. The latter form has more in common with “anchorate” spicules from the Atdabanian (Cambrian Stage 3) Bagrad Formation of the Batenev Range, Altay Sayan Foldbelt ( Sugai et al. 2004), which in addition to pentactines include elements with short duplicated paratangential rays. Spear-shaped spicules occur in the lower Tommotian stage Emyaksin and Erkeket formations ( Kouchinsky et al. 2015a: fig. 70A and Fig. 71L herein), but their morphology varies including hexactines, with an additional ray directed away from the axial ray ( Kouchinsky et al. 2015a: fig. 70B), as well as pentactines with their axial ray diverging from the axis of symmetry of the spicule ( Fig. 71K ).

Other siliceous spicules in the assemblage from sample 11/18.7 herein include polyactine megascleres with acutely tapering slim slightly curved rays ( Fig. 71A–D, H, J ). Among them, there are tetractines ( Fig. 71A ) with three acutely tapering straight rays arranged in the same plane at an angle 120° from each other (paratangential rays) and a thicker straight axial ray perpendicular to them. This ray, as well as one of the radial rays, branch dichotomously at 120° to each other. Additional short stubby spines may be present at the external surface of paratangential rays ( Fig. 71A ).

Fedorov in Pegel et al. (2016) compared these spicules with plagiotriaenes and phyllotriaenes of “lithistid” sponges and with diactines but these spicules are modified tetractines. Some demosponge ectosomal phyllotriaene megascleres resemble closely Bistella Fedorov in Pegel et al., 2016, in both morphology and size range (e.g., Schuster et al. 2015: fig. 4C). Morphologically these elements are comparable with homosclerophorid tetractines and polycystine radiolarian) point-centered spicules but are much larger following the data of Uriz (2006) on extant sponges and of Maletz (2011) for the oldest siliceous polycystines. However, their co-occurrence with typical hexactinellid spicules in the same sampling sets does not exclude the association of both spicule types to the same sponge skeletons.

Figures

Fig. 71. Hexactinellid spicules from the lower Cambrian Erkeket (A–F, H–J, L–O) and Yunkyulyabit-Yuryakh (G) formations, Khorbusuonka River and Emyaksin Formation, Bol’shaya Kuonamka River (K), Siberia, Russia; samples 11/18.7 (A–F, H–J, L), 11/16.05 (M, N), 19/107 (G), 20/1B (O), and 6/0.3 K). A–D, H, J. Polyactine siliceous megascleres with acutely tapering slim curved rays, SMNH Sp11424–11429, respectively. E, F, I, M–O. Pentactines and hexactines with thin smooth rays, SMNH Sp11417–11422, respectively. G. Fragment of a pinnular pentactine, SMNH Sp11423. K, L. Abnormisella sp., SMNH Sp11415 (K) and 11416 (L). Scale bar: 250 µm (A–D, H–J, O) and 500 µm (E–G, K–N).