Digestive structures in Ordovician trilobites Colpocoryphe and Flexicalymene from the Barrandian area of Czech Republic

Abstract

Two recently discovered specimens of the abundant calymenoid trilobite Colpocoryphe Novak in Perner, 1918 from the Middle Ordovician Sarka Formation and one specimen of Flexicalymene (Flexicalymene) pragensis Vaněk & Vokac, 1997 from the Upper Ordovician Bohdalec Formation, all from the Prague Basin, display remains of the digestive system. In Colpocoryphe, an internal mould of an articulated exoskeleton contains a post-stomach part of the alimentary canal preserved through the narrow axial region of the occipital ring, all thoracic segments as well as in the axial part of the pygidial shield. The anterior part of the digestive system is poorly known as the specimen shows the hypostome preserved in situ and the space between the glabella and the hypostome is represented by an empty cavity associated with probable remains of gut diverticulae on both sides of the cephalon. The second, incomplete specimen consists of five posterior thoracic segments articulated with the pygidium. The axial region of this specimen is preserved with a clearly discernible segmented intestine which terminates at the axial tip and then bends ventrally. In an enrolled specimen of Flexicalymene pragensis, supposed remains of the alimentary tract are comparatively poorly preserved but discernible in the middle and posterior parts of the thoracic axis and in the anterior part of the pygidial axis. Digestive structures within the family Calymenidae have not been described previously. Earlier discoveries of the digestive system in Ordovician trilobites of the Barrandian area are briefly reviewed.