Kirkocystid ankyroids (Stylophora: Echinodermata) from the Šárka Formation (Ordovician) of Bohemia


Authors: Parsley RL, Prokop RJ, Derstler K

Published in: Bulletin of Geosciences, volume 75, issue 1; pages: 37 - 48;

Keywords: Stylophora, Kirkocystida, Ankyroida, Šárka Formation, Ordovician, functional morphology,

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Kirkocystids were originally described as the cirriped genus Anatifopsis Barrande, 1872 . Now recognized as stylophoran echinoderms, kirkocystids from the Llanvirn age Šárka Formation are represented by two monospecific genera: Anatifopsis (= Anatiferocystis Chauvel, 1941) bohemica Barrande, 1872 and Sagittacystis gen. nov. (= Balanocystites Barrande, 1887) prima (= Anatifopsis prima Barrande, 1872). During Arenigian, kirkocystids probably evolved from Peltocystis-like ancestors in the relatively dysaerobic Prague Basin which seems to be the centre for dispersal for subsequent representatives found in the Western United States. The kirkocystid theca has been reduced to six plates, dominated by the paired adorals, but within the subclade the aulacophore has remained conservative and primitive. Like in most ankyroids kirkocystid thecae are flexible, but quite exceptionally, they could apparently expand and contract along dorsal and ventral sutures of the right adoral. Juvenile specimens indicate that ontogenetic development accentuates plate growth towards the thecal posterior.