Hyolithellus 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 : 431-433

Hyolithellus sp.

Fig. 65A, F, H .

Material.—Several hundred fragmentary calcium phosphatic tubes, including figured SMNH X11299–11301, from samples 15/23, Chuskuna Formation (Kessyusa Group), Watsonella Zone, Cambrian Stage 2, 11/16.1, 11/16.5, 11/18.7, 11/21.6, Erkeket Formation, Khorbusuonka River and 21/22, Tyuser Formation, Lena River, Dokidocyathus regularis Zone, Tommotian stage (correlated with the upper part of Cambrian Stage 2), 19/3.25, 19/4.25, 19/14.25, 19/16, Botoman stage (Cambrian Stage 4), 19/25.5, 19/26.75, 19/29, 19/46.5, 20/4B, 20/5B, Toyonian stage (Cambrian Stage 4), Khorbusuonka River, 21/51, Delgadella anabara – Nevadella Zone, Atdabanian stage (Stage 3), and 22/0, Tyuser Formation, Bergeroniellus micmacciformis –Erbiella Zone, Botoman stage (Stage 4), lower reaches of the Lena River. Siberia, Russia.

Remarks.—Slightly irregularly curved very slowly expanding tubes with circular cross-section, up to 300 µm in diameter. External surface smooth or with faint transverse folds perpendicular to the longitudinal axis of the tube. Hyolithellus sp. lack longitudinal striation and regularly spaced ribs.

Family Torellellidae Holm, 1893

Genus Torellella Holm, 1893

Type species: Hyolithes laevigatus Linnarsson, 1871 ; lower Cambrian ; Sweden .

Torellella spp.

Figs. 65G, I–L , 66 .

Material.—Several hundred calcium phosphatic tubes and fragments, including figured SMNH X11302–11314, from the Erkeket and Tyuser (sample 22/0) formations. Samples 11/18.7, 11/21.6, 11/28.8, Khorbusuonka River, 21/21, 21/22, 21/22.7, 21/33, Lena River, Tommotian stage (correlated with the upper part of Cambrian Stage 2), 19/1.5, 19/3.25, 19/4.25, 19/5.5, 19/14.25, 20/1B, 20/2B, Khorbusuonka River, and 22/0, Lena River, Botoman stage (Cambrian Stage 4). Siberia, Russia.

Remarks.—Specimens in Fig. 65K, L are similar to Torellella biconvexa Missarzhevsky in Rozanov et al., 1969. They have lenticular cross-section and frequent weak transversal growth lines, diverging at ca. 10°, slightly undulating and curved predominantly in a single plane of their narrow sides. Specimens in Fig. 65I, J are similar to Torellella mutila Missarzhevsky, 1989 ( Missarzhevsky 1989: 195, pl. 24: 8) from the Bergeroniellus micmacciformis –Erbiella Zone, Botoman stage of the middle Lena River. The form is also similar to T. biconvexa , but is predominantly irregularly curved in a single plane. A longitudinal furrow can be observed on narrow sides of the tube ( Fig. 65I ) and a fragment ( Fig. 65G ). Similar furrows are described from Torellella cf. laevigata by Kouchinsky et al. (2015a).

Tubes of Hyolithellus sp. and Torellella sp. are perforated by circular, oval and rounded rectangular holes, 20–60 µm across ( Fig. 66 , see also Kouchinsky et al. 2015a). Rare perforated tubes of Hyolithellus sp. and Torellella sp. , otherwise identical to non-perforated ones, were first mentioned and illustrated by Repina et al. (1974: 72, 73, pl. 19: 3, 4; pl. 15: 1, 3) from the upper Dokidocyathus regularis Zone, Tommotian stage of the Chekurovka section in lower reaches of the Lena River. Other co-occurring fossils do not show such perforations, implying that Hyolithellus and Torellella had similar properties of their organophosphatic tubes corroborating their affinity to the same animal clade.

Bifurcating and irregularly curved, ca. 10 µm thick galleries are found on a single fragment of Torellella sp. from lower Botoman stage ( Fig. 66H ). The galleries are generally subparallel to the tube surface, with only a few branches directed perpendicularly to the surface. The latter type of bioerosion has not yet been described from hyolithelminths and was likely bored by an organism different from a producer of thicker perpendicular canals (holes) available in other fragments. The shape of the holes in Hyolithellus and Torellella tubes depend on plywood arrangement of multiple layers with orthogonal orientation of the constituent fibres. In thinner walls in Hyolithellus , rounded and circular holes predominate. Rectangular pores occur in thicker tubes of Torellella , where they penetrate through multiple alternating laminae having mutually orthogonal orientation of fibers.

Figures

Fig. 65. Calcium phosphatic tubes of hyolithelminths from the lower Cambrian Erkeket Formation, Khorbusuonka River (A–C, G–J) and Tyuser Formation, lower reaches of the Lena River (D–F, K, L), Siberia, Russia; samples 11/19.5 (B, C), 19/3.25 (H, J), 19/4.25 (I), 19/5.5 (G), 19/16 (A), 21/21 (D, E, K), and 21/22 (F, L). A, F, H. Hyolithellus sp., SMNH X11299–11301, respectively. B–E. Hyolithellus isiticus Missarzhevsky in Rozanov et al., 1969, SMNH X11295–11298, respectively. G, I–L. Torellella spp., SMNH X11302–11306, respectively. Scale bar: 1 mm (D, L), 500 µm (A–C, E, F, H, I–K), and 250 µm (G).

Fig.66. Torellella spp. with evidences of bioerosion, from the lower Cambrian Erkeket Formation,Khorbusuonka River (A–C, E, G) and Tyuser (F, H) and Sekten (D) formations, lower reaches of the Lena River, Siberia, Russia; samples 19/4.25 (A), 19/5.5 (E), 19/14.25 (B), 20/1B (C, G), 21/129 (D), and 22/0 F, H). A–G. Fragments of calcium phosphatic tubes penetrated by sub-vertical canals, SMNH X11307–11313, respectively. E2, close-up of E1 showing perforations. H. Fragment of tube with canals sub-parallel to the surface, SMNH X11314. Scale bar: 500 µm (A–D), 250 µm (E1, F–H), and 80 µm (E2).