Cystoid

Paulicystis densus

• Silurian
• Massie (formerly Osgood) Shale
• New Point Stone Quarry, Napoleon, Ripley County, Indiana, USA

Size: 2.5 cm

Another diploporite cystoid from Napoleon. Paulicystis is characteristically spherical and compact, with a widely-flaring base by which it attached to the seafloor. It bears a 4-pointed "mouth" for the attachment of its 4 brachioles, with the anal opening located next to it. You may also notice the complex maze-like channels etched into its thecal plates. These are called "humatipores" and are thought to have served a respiratory function. There are actually two species of Paulicystis found in Napoleon, distinguished by the density of these humatipores; this one is aptly named P. densus for the more densely-packed pores, and is the more common species.