Mucrospirifer is a genus of extinct brachiopod of the order Spiriferida. This genus is sometimes known as the “butterfly shells.” Fossils of this genus occur mostly in the Middle Devonian strata. When alive, this genus mainly lived in muddy marine sediments, and were attached to the sea floor via its pedicle (foot).

The bi-convex shell was about an inch long, and sometimes grew to 1.6 inches. The shell has a fold, groove and rod-like structure. It is elongated along the hinge line, which extends outward to form sharp points, giving them a wing-like appearance. The apex of the pedicle valve contains a small fold. The shell looks like two seashells stuck together.

Like other brachiopods, this animal was a filter feeder. There are 13 known species of Mucrospirifer.

Image Caption: Mucrospirifer fossil. Credit: DanielCD/Wikipedia(CC BY-SA 3.0)