Torellella sp.

Clausen, Sébastien & Álvaro, J. Javier, 2006, Skeletonized microfossils from the Lower-Middle Cambrian transition of the Cantabrian Mountains, northern Spain, Acta Palaeontologica Polonica 51 (2), pp. 223-238 : 230

Torellella sp.

Fig. 4G–K .

Material.—More than 100 phosphatic tubes and fragments from Lower Cambrian ooid packstones, sections V 1 and Cr 1–4.

Description.—Phosphatic, elongated, tube fragments of narrow shape and elliptical cross−section. Keels are faint or not developed. Tubes show a distinct irregular and curved growth pattern, both laterally and dorsoventrally. Thickness of tubewalls ranges between 5 to 15 µm. No different shell−layers are visible. The angle of divergence is not constant and increases sharply near the narrowest (proximal) part of the tube. The largest (distal) part of each tube is clearly more elliptical in cross−section. Most specimens display faint growth lines (furrows; Fig. 4G, H ) and/or faint, oblique to transverse riblets ( Fig. 3I) on outer surfaces: these structures are sometimes very regular to relatively irregular, and depend on the relative position of the curvature. Ring−like or other morphological characters are not observed on outer surfaces.

Remarks. —Even if the multi−layered structure of the wall is rarely preserved, external morphological characters of these tubes can be related to Torellella lentiformis ( Sysoyev, 1960) . However, Sysoyev (1962) described the lateral keels in this species as “sharp”, and Sokolov and Zhuravleva (1983) as “distinct”, in contrast with the “faint or not developed” keels of the Cantabrian sclerites. Calcitic skeletons, described in thin section, including hyolith, trilobite and echinoderm remains ( Álvaro et al. 2000b), were not released from limestones owing to lack of epigenesis; as a result, it can be assumed that the composition of etched specimens was phosphatic in origin. Numerous specimens exhibit rounded to elliptical holes on their walls ( Fig. 4I ). Even if their shape and the original phosphatic composition of the walls suggest they are active perforations (bioerosion and/or predation), they may be related to preservational artifacts, and thus, further study is needed before to conclude on their formation pattern.

Numerous unidentified phosphatic (fragmented) tubes occur with Torellella sp. One of these phosphatic tubes ( Fig. 4K ), 0.8 mm long, is broadly straight, with a circular to irregularly deformed cross−section (up to 150 µm in diameter), curved irregularities and exhibits an angle of divergence of its subparallel sides of ca. 5 °. The circular cross−section suggests relationship either with Hyolithellus or other tubular taxa (either phosphatic or calcareous in origin). Nevertheless, the buckled appearance, which is difficult to differentiate from deformational features, is unusual in this genus. In conclusion, this tube cannot be properly assigned within the hyolithelminths.

Figures

Fig. 4. Scanning electron micrographs of skeletonized microfossils from the Lower–Middle Cambrian transition of the Esla Nappe, Cantabrian Mountains, Spain. A, B. Chancelloria sp. A; chancelloriid sclerites; section Cr4, “Beleño” facies, upper member of the Láncara Formation, early Leonian. A. DGO 21129, longitudinal section. B. DGO 21130, lateral view. C–E. Chancelloria sp. B; chancelloriid sclerites; section Cr4, “Beleño” facies, upper member of the Láncara Formation, early Leonian. C. (1+6) sclerite, DGO 21131, lateral views. D. (1+5) sclerite, DGO 21132, upper view. E. Incomplete (1+7) sclerite, DGO 21133, upper view. F. Parazhijnites cf. guizhouensis Qian and Yin, 1984; cambroclavid sclerite; section Cr4, “Beleño” facies, upper member of the Láncara Formation, early Leonian; DGO 21134, oblique (F1) and lateral (F2) views. G–J. Torellella sp.; hyolithelminth tubes; section Cr4, ooid/bioclastic limestone, lower member of the Láncara Formation, latest Early Cambrian. G. DGO 21135, lateral view. H. 21136, lateral view. I. DGO 21137, lateral view showing elliptic perforation (I1) and detail of the faint growth lines (squared area on I1; tilt adjust). J. DGO 21138, lateral (J1) and distal (J2) views. K. Phosphatic undefined tube; section Cr4, ooid/bioclastic limestone, lower member of the Láncara Formation, latest Early Cambrian; DGO 21139, lateral view (K1) and detail of broken termination (K2). Scale bars 250 µm, except I2 and K2 for which are 50 µm.