Brachiopods 3: Meekella
Phylum Brachiopoda Meekella
The surface of Meekella looks like the ruffles of a curtain. Such coarse surface folds are called rugae: they are visible on the inside of the shell as well. Cross sections of this species appear zig-zag because of the plications of the shell.
Meekella and Derbyia occur only in rocks of the Pennsylvanian and Permian Periods. Because of this restricted time zone, the fossils are guide fossils. We can use them to date rocks. Many sedimentary rock units are dated in this way.