Pentamerids differ from other articulates in the structure of the rear portion of the pedicle valve, which has a spoon-shaped structure called a spondylium. The shell microstructure is impunctate. The shell is often five-sided (pentagonal) in outline - hence the name. The hinge line is short. The fold and the sulcus are reversed in regard to other brachiopods, with the fold on the pedicle valve.
These biconvex (left) shells appeared in mid-Canibrian seas, became common in the Ordovician, and lived on to the end of Devonian times. The Silurian Pentamerus laevis lived in closely packed colonies with pedicles sunk into the mud and elongate shells directed upward. Such colonies are often found on the under side of beds of fine sandstones. When cleaned and exhibited in museums, they appear upside down. Often there was pedicle attachment at all, and the animals lived in self-supporting colonies like the one illustrated above.
Porambonitoidea (? Early Cambrian-Early Silurian)
Camerrelloidea (Early Ordovician-Early Devonian)
Pentameroidea (Late Ordovician--Late Silurian)
Clorindoidea (? - ?)
Stricklandioidea (Early Silurian-Late Silurian)
Gypiduloidea (Early Silurian-Late Devonian)
Classification from Classification des Brachiopoda (Lophophorata)
Brachiopoda main page