Etacystis

Etacystis communis, colloquially known as the H-animal or aitch, was a soft-bodiedinvertebrate that lived in shallow tropical coastal waters of muddy estuaries during the Pennsylvaniangeological period, about 300 million years ago. The classification is uncertain: the animal was likely colored red and had a unique H-shaped body ranging from 2 to 11 cm long, and researchers have suggested a hemichordate or hydrozoan affinity. However, the animal did not possess a stomochord. Examples of Etacystis have been only found in the Mazon Creek fossil beds of the Midwestern United States.