Mucrospirifer is a genus of extinct brachiopods in the class Rhynchonellata (Articulata) and the order Spiriferida. They are sometimes known as "butterfly shells".[2] Like other brachiopods, they were filter feeders. These fossils occur mainly in Middle Devonian strata[2] and appear to occur around the world, except in Australia and Antarctica.[1][3]
The biconvex shell was typically 2.5 cm long,[2] but sometimes grew to 4 cm. The shell of Mucrospirifer has a fold, sulcus and costae. It is greatly elongated along the hinge line, which extends outward to form sharp points.[2] This gives them a fin- or wing-like appearance. The apex area (umbo) of the pedicle valve contains a small fold for the pedicle.[2] Mucrospirifer lived in muddy marine sediments, and were attached to the sea floor via the pedicle. The shell sometimes looks like two seashells stuck together.