Abstract
An extensive sample of well-preserved conulariids from the Pennsylvanian of the North American Midcontinent (Texas and Oklahoma, USA) have been studied using X-ray micro-Computed Tomography (µCT) and have shown structures identified as longitudinal muscle bundles and a potential gastric cavity. These unequivocal structures appear in several specimens coming from different sites. Their preservation varies from a gastric cavity with muscle bundles in some individuals to only longitudinal muscle bundles in others. The muscle bundles fuse apically or medially, normally forming V-shaped pairs, and they extend along the theca/exoskeleton, parallel to the corner, towards the aperture. Longitudinal bundles have predominant perradial positions. Although there have been some articles on conulariid soft parts, most of them refer to relic soft parts. This is the first time that these structures are shown using µCT. Discovery of conulariid soft parts contributes to knowledge of metazoan evolutionary history.