The holdfast of Finitiporus boardmani (Echinodermata: Diploporita) in the Silurian Massie Formation of the Cincinnati Arch region, USA

Abstract

A attachment structure, attributable to the sphaeronitid diploporitan Finitiporus boardmani Frest and Strimple, is documented herein from a hardground surface within the well-known middle Silurian (Wenlock) Massie Formation at the Napoleon quarry of southeastern Indiana, USA. This attachment structure is composed of multiple elongate plates lacking macroscopic pores, terminating in a slightly expanded disc. No portion of the theca is articulated to the specimen, though the morphology of the attachment structure is sufficiently distinctive to permit confident identification. The holdfast was dislodged from its attachment substrate but is present in the area immediately surrounding a bryozoan-micrite microbioherm, suggesting that F. boardmani occupied such elevated, hard environments. As the densely encrusted hardground containing this specimen has been partially destroyed since the initial report on pelmatozoan holdfasts, documentation of this occurrence is important for accurately recording of the total diversity and environmental distribution of echinoderms at an important locality.