Hyolithellus, Billings, 1871

Kouchinsky, Artem, Bengtson, Stefan, Clausen, Sébastien & Vendrasco, Michael J., 2015, An early Cambrian fauna of skeletal fossils from the Emyaksin Formation, northern Siberia, Acta Palaeontologica Polonica 60 (2), pp. 421-512 : 497

Hyolithellus cf. H. insolitus Grigor’eva in Voronin et al., 1982

Fig. 67A, C, D, F .

Material.—Several calcium phosphatic tubes, including SMNH X 4798–4801, from samples 7/19, 7/36.7, and 7/39.5. Emyaksin Formation, Bol’shaya Kuonamka River; correlat- ed with the Dokidocyathus lenaicus Zone, Tommotian Stage

(sample 7/19) and Delgadella anabara Zone, Atdabanian Stage.

Description.—Straight, slightly diverging, a few mm long, fragments of tubes with circular cross-section, 0.2–0.6 mm in diameter ( Fig. 67A, C, D, F ). The external ornamentation consists of weak concentric ribs and faint longitudinal ridges and furrows undulating between the ribs.

Remarks.—The forms herein are similar to Hyolithellus insolitus Grigor’eva in Voronin et al., 1982 described from the lower Cambrian of Mongolia (see also Esakova and Zhegallo 1996) and southeastern Siberian Platform ( Sokolov and Zhuravleva 1983). Other forms illustrated herein under Hyolithellus sp. ( Fig. 67B, E, G ) lack longitudinal striation. H. insolitus or similar tubes with transversal annulation and longitudinal stiation are also reported from the lower Cambrian of India ( Brasier and Singh 1987), South China ( Esakova and Zhegallo 1996), Australia ( Skovsted and Peel 2011), lower–middle Cambrian of Laurentia ( Skovsted and Holmer 2006), and middle–upper Cambrian of Kazakhstan ( Esakova and Zhegallo 1996).

The tubes from samples 7/36.7, 7/39.5, and an eroded specimen of Hyolithellus sp. from sample 7/25.6 ( Fig. 67E ), have numerous circular or oval to rounded sub-rectangular holes, 20–60 μm in diameter, in their wall. These are interpreted to result from bioerosion which occured before deposition into the sediment (see Discussion in Torellella below). According to Skovsted and Holmer (2006), the species may be a junior synonym of H. grandis Missarzhevsky in Rozanov et al., 1969, but the holotype of the latter is much larger and preserved on the rock slab.

Figures

Fig. 67. Hyolithelminths from lower Cambrian Emyaksin Formation, Bol’shaya Kuonamka River and Malaya Kuonamka River, Anabar Uplift, Siberia. A, C, D, F. Hyolithellus cf. H. insolitus Grigor’eva in Voronin et al. 1982. A. SMNH X 4798, sample 7/19; longitudinal view. C. SMNH X 4799, sample →