The Dala thumb: shell morphology and failed predation in Pollicina cyathina (Gastropoda) from the Ordovician of Dalarna, Sweden

Abstract

ABSTRACT The distinctive, tall and slender cyrtoconic shell of the gastropod Pollicina cyathina Koken, 1897, originally established on a poorly preserved internal mould from the Middle Ordovician of the Dalarna region of central Sweden, is redescribed on the basis of additional material from several localities in the vicinity of Rättvik. Repaired injuries preserved in the fine comarginal growth lines of the archinacelloidean gastropod indicate failed durophagous predatory attacks. Unusual apical structures on an internal mould from Sjurberg probably result from closure of the earliest growth stages later in ontogeny.