Fossil of the Echinodermata Leiopedina tallavignesi found in Navarcles (Bages).
The sea urchins are the most frequent amongst the fossil Echinodermata in the district of Bages. They are just marine animals. They have a made of welded plates calcium carbonate shell with lumps where to assemble the spines. The sea urchins are striking fossils since they are often well preserved, though the skeleton and the spines rarely are found all together. Sea urchins are globular or flat, with radial or bilateral symmetry. [photo Joaquim Sanz / Museum of Geology Valentí Masachs]
See also the article Pedres milionàries, in Catalan, by Jordi Badia.