Early ontogeny of the Cambrian trilobite Sao hirsuta from the Skryje-Tyrovice Basin, Barrandian area, Czech Republic

Preservation of onto genetic stages of trilobites from the Cambrian of the Skryje-Tyrovice Basin (Barrandian area) has been known from several localities in the upper part of the Buchava Formation. The most complete information on exoskeletal changes during ontogeny was based on material assigned by Barrande (1852) to Sao hirsuta. Based on quantitative methods and detailed study of the morphology of the exoskeleton, we recognize three protaspid and two early meraspid instars of Sao hirsuta. We also describe the protaspid stages of two indeterminate taxa of Ptychopariida, one originally determined as the protaspides of Sao hirsuta and the other referred to by Ruzicka (1943) as Barrande's larva. Protaspides of Sao hirsuta have an adult-like morphology, and their presumed benthic mode of life is consistent with the restricted palaeogeographic distribution of this genus.