Allonnia 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 : 226

Allonnia sp.

Fig. 3J.

Material. —About 20 specimens preserved as phosphatic steinkerns in the Middle Cambrian “Beleño” facies, section Cr 4.

Description.— (3+0) sclerites (rarely exceeding 0.7 mm of length, most distal parts of the rays eroded off) having rays of equal width, thin, slender, and tapering, each with a round to weakly elliptical aperture (foramen) located on a swollen base. Remarks. — Even if there is good evidence from completely preserved Burgess Shale chancelloriids that at least some forms with Allonia tripodophora − type sclerites ( C. eros Walcott, 1920 type 2 sensu Bengtson, in Bengtson et al. 1990) have a unimembrate scleritome with three rays in each spicule, variability within the Allonia scleritome remains poorly known (see for example A. junyuani Janussen et al. 2002 ). Allonia tripodophora differs from A. erromenosa Jiang in Luo et al. 1982, also (3+0), in the presence of a distinct external boundary between the rays and an angle of approximately 45–80 ° from the basal plane. C. racemifundis Bengtson, 1990 (in Bengtson et al. 1990), which may also contain 3−rayed sclerites, differs in the shape of the base. Formal comparisons with the various Allonia species are precluded because of the inadequate, phosphatic−steinkern preservation of the chancelloriid sclerites described here. In conclusion, open nomenclature seems more appropriate for these specimens.