The Lower Ordovician trilobite Krattaspis: the earliest cyrtometopinid (Cheiruridae) from the Arenig of the east Baltic

The type specimen of Krattaspis viridatus Öpik, 1937, one of the earliest known representatives of the family Cheiruridae, is redescribed in order to clear up the confusing characters caused by distortion of the exoskeleton. More than 50 new specimens from different localities in the Baltic-Ladoga Clint area contain three species, the type species and two that are new (K. popovi sp. nov. and K. vitalis sp. nov.); all come from the Arenig Billingen Stage, from different units. A meraspid cephalothorax and a thoracopygon of K. vitalis have been found together with some adults, and show some characters of ontogeny of that taxon. The systematic validity of the subfamily Cyrtometopinae Öpik, 1937 is discussed.