Chancelloria sp. A

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 : 228

Chancelloria sp. A

Figs. 3M, N, 4A, B .

Material.—About 20 specimens from the Middle Cambrian “Beleño” facies, section Cr 4.

Description.—Sclerites with a tapering central vertical ray (0.5 to 0.7 mm in length) and five to seven prominent, recurved, radiating lateral rays; lateral rays are asymmetrically arranged and commonly differ in size; the curvature of rays is greatest at the intersection with the central ray; they are relatively straight, and make an acute angle (less than 30 °) with the central ray; diameter of the sclerite can reach 0.6 mm, whereas the maximum diameter of the central ray is 0.4 mm; specimens commonly have five to six lateral rays, although a few have seven; they are oval to subrectangular in cross−section, except for the tips, which are round in outline, whereas the whole central ray is round in cross−section except at its polygonal base; specimens are slightly longer (central ray) than large (including lateral−ray outline), with a ratio varying from 1 to 1.5. Specimens cut longitudinally ( Fig. 4A ) show an inner cavity along the central ray, subtriangular in section, bounded (except at the basal foramen) by a wall, ca. 30 µm thick.

Remarks.—Some specimens of Chancelloria eros from the Lower Cambrian of the United States ( Mehl 1996: fig. 1D) and the Middle Cambrian of Australia ( Mehl 1998: pl. 7: 7–8) show similar robust rays, although they have a distinct flat base and flat marginal rays, and the Cantabrian sclerites are prominently recurved. The morphology of the Cantabrian sclerites mimics that of paraclavules, interpreted as anchorate root−tuft spicules by Mehl (1996) in hexactinellids associated with dermal or gastral membranes ( Mehl 1998), and is also similar to the siliceous spicules of Nabaviella Mostler and Mosleh−Yazdi, 1976 (sensu Bengtson et al. 1990). Nevertheless, they do not only differ in their composition (most probably secondarily phosphatized calcareous sclerites, not siliceous in origin) but also in the presence of basal foramina. Although some Late Cambrian–earliest Ordovician pelmatozoan holdfasts share close morphological similarities, their size, microstructure and inner cavities are different ( Sumrall et al. 1997; Álvaro and Colchen 2002).

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.