Abstrakt
The gogiid eocrinoid Akadocrinus jani Prokop, 1962 is known from the mid-Cambrian (Drumian) Jince Formation of the Pribram-Jince Basin (Barrandian area, Czech Republic). Excellently preserved specimens of this species are described in detail. Our primary focus was on juvenile specimens, described here for the first time. Detailed comparison among juvenile specimens makes it possible to establish changes in morphology during ontogeny. Juvenile specimens differ considerably from adult specimens in (1) a lower number of thecal plates, (2) a complete absence of epispires, (3) comparatively shorter brachioles, comprising a small number of brachiolar plates, (4) a comparatively shorter stem, comprising a small number of columnals and (5) a relatively large attachment disc. Study of the Jince material makes it possible to establish two basic phases in the development of Akadocrinus: the pre-epispire bearing phase and the epispire bearing phase.