Cotyledion

Cotyledion tylodes is an extinct, stalked filter-feeder known from the Chengjiang lagerstatten. The living animal reached a couple of centimetres in height, and bore a loose scleritome of ovoid sclerites. Its interpretation has been controversial, and it has been previously identified as a carpoid echinoderm, or as a stem group echinoderm. C. tylodes is now classified as a stem group entoprocta based on new fossils that clearly show a U-shaped gut and a crown of tentacles. This entoproct interpretation of Cotyledion, however, has been questioned by Mark McMenamin, who considers it best interpreted as a stem group echinoderm based on the morphology of its stem sclerites.