Torellella, Holm, 1893

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 : 497-499

Torellella cf. T. laevigata (Linnarson, 1871)

Fig. 67H–M .

Material.—Several calcium phosphatic tubes, including SMNH X 4805–4810, from samples 3/25, 6/6.6, 6/14, 7/25.5, 7/27.5, 7/33, and 7/36.7. Emyaksin Formation, Malaya Kuonamka and Bol’shaya Kuonamka rivers; correlated with the Dokidocyathus regularis Zone, Tommotian Stage – Delgadella anabara Zone, Atdabanian Stage.

Description.—Undulating and/or curved tubes, diverging at 10–15°, with transversal outline rounded at the initial part ( Fig. 67H 2 , L) but lenticular at the aperture. The external ornamentation consists of frequent concentric growth lines. A longitudinal continuous narrow furrow ( Fig. 67L, M ) marks each narrow keel-like side of the tubes.

Remarks.—The fossils are also similar to T. lentiformis ( Sysoev, 1960) , and the latter may be a junior synonym of T. laevigata (Linnarson, 1871) . Longitudinal ornamentation of the narrow sides is not, however, described from the latter two forms. Commonly attributed to Torellella Holm, 1893 , the fossils are also very similar to those described from the Qiongzhusian–lower Canglangpuan Stages of China as Sphenothallus Hall, 1847 ( Li et al. 2004b). The middle Qiongzhusian Torellella bisulcata Li, 2004 and lower Cambrian T. lentiformis have a narrow sulcus along each of the narrow sides, similar to longitudinal furrows in Torellella cf. T. laevigata herein.A single apical fragment with a flared open attachment structure is also present in the material described ( Fig. 67I ).

Fragments of Torellella sp. ( Fig. 68 ) demonstrate that the wall, originally phosphatic in composition, consists of multiple layers arranged in a plywood stucture, where adjacent layers have orthogonal orientation of the constituent fibers ( Fig. 68D 1 ; see also Bengtson et al. 1990, Skovsted and Peel 2011). Tube fragments of Torellella from samples 6/66.2, 7/25.6, 7/30, 7/39.5, and 7/60 are eroded and perforated by numerous rounded-squared or rounded-rectangular holes, 20–60 μm in diameter ( Fig. 68 ). In some fragments, the holes incompletely penetrate the wall from the inside of tube ( Fig. 68A ) and, therefore, are unlikely the result of attacks by a predator from outside. In other specimens, the perforations are combined with eroded outer and inner surfaces ( Fig. 68D – G ). Some of the holes have rounded broken-off edges ( Fig. 68B 2 ), demonstrating that erosion had taken place after the holes were formed and before deposition into the sediment. These holes expand moderately inwards into the tube wall, and their margins are oriented parallel to the orthogonal direction of fibers in the wall ( Fig. 68C ). Similar holes in the wall are found in Hyolithellus , but other fossils described herein. They are also observed in hyolithelminths from Series 2 of Laurentia (Christian Skovsted and AK, unpublished observation 2012). Thus, it appears that the perforations have a biological origin (e.g., sponge galleries or holdfasts attachment sites), made before deposition of abandoned tubes into the sediment.

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 →

Fig. 2. Derivation of fossiliferous samples (arrows with numbers) and chemostratigraphic correlation of sections 1 and 3 (Malaya Kuonamka River) with sections 6 and 7 (Bol’shaya Kuonamka River). Correlation with carbon isotope features II–VII from stratotypes of south-eastern Siberian Platform (Brasier et al. 1994) according to Kouchinsky et al. (2001). Note that the zero level in all sections corresponds to the water level above which the sections were exposed in 1996. Description of fauna from the lower part of the Emyaksin Formation in complementary outcrops at the Bol’shaya Kuonamka River (below that zero level) will be published elsewhere. Fauna from the overlying Kuonamka Formation is published by Gubanov et al. (2004) and Kouchinsky et al. (2011).

Fig.68.Hyolithelminths Torellella sp. from lower Cambrian Emyaksin Formation, Bol’shaya Kuonamka River,Anabar Uplift,Siberia; erosion of tubes.A. SMNH X 4811, sample K6-4B; A 1, general view on the inner surface of the tube fragment; A 2, close-up of A 1 showing a rounded squared hole partially penetrating the wall. B. SMNH X 4812, sample 7/30; B 1, general view on the inner surface of the tube fragments; B 2, rounded edge of the tube fragment with penetrating holes; B 3, close-up of B 2; B 4, close-up of B 1. C. SMNH X 4813, sample 7/30; general view on the inner surface of the tube fragments. D. SMNH X 4814, sample 6/66.2; D 1 , close-up of D 2 , orthogonal orientation of fibres in adjacent layers of the wall; D 2 , general view of an eroded fragment of tube. E. SMNH X 4815, sample 7 /25.6; view on the outer surface. F. SMNH X 4816, sample 7/60; broken edge of a tube fragment with layers in the wall penetrated by holes. G. SMNH X 4817, sample 7/39.5; view on the inner surface. Scale bar: A , B , D , E, G, 600 μm; C, F, 300 μm; B , 120 μm; B , D , 60 μm; A , 30 μm; B , 20 μm.

Fig. 1. Map showing location of sections 1, 3, Malaya Kuonamka River; 6, 7, Bol’shaya Kuonamka River.