Fossil specimen of the gastropod *Platyceras* sp. attached to the calyx of the crinoid *Arthracantha carpenteri*; specimen is from the Devonian Arkona Shale of Ontario, Canada (PRI 76784). Specimen is from the collections of the [Paleontological Research Institution](http://www.priweb.org), Ithaca, New York. Longest dimension of specimen is approximately 3.5 cm. Model by Emily Hauf.