Brachiopods (or lamp shells) are members of the Phylum Brachiopoda, which was very successful during the Paleozoic and has survived, though at much reduced diversity, to the present day. Brachiopods were (are) marine animals enclosed in a pair of shells of unequal size.
A brachiopod shell has a mirror symmetry
Each side of the brachiopod has a plane of symmetry bisecting it (unlike the bivalve molluscs where the plane of symmetry runs between the shells, which are equal in size). They are filter feeders that generally live attached to the sea floor. Geologic range of brachiopods is surprisingly long, from the Cambrian to present.
Brachiopods were much more abundant in the past than they are now, there being only several hundred species today and many thousands of fossil forms. Living brachiopods are distributed worldwide, found from high tide line to the deep depths.
Brachiopods had their origins in the Precambrian period. In Cambrian times, the inarticulates became dominant, but by Ordovician times the articulate groups rapidly exploded into existence, overwhelming other marine invertebrates until their great decline during the Permian extinctions. Living brachiopods are great living fossils. Specimens of these relic forms are available at many sea shell dealers and one or two examples should be included in your fossil collection.
Today's living brachiopods
Paleozoic brachiopods in limestone
After the PERMIAN EXTINCTION which affected almost all life forms on earth, practically all Paleozoic groups became extinct, only a few survivors straggled into the Mesozoic and Cenozoic eras.
Brachiopods (I call them "brachs") are very common. There are thousands of different kinds, are one of the most common fossil you will have in your Arizona collection. Complete, well-preserved brachiopod shells are prized in any fossil collection and are valuable in their paleontological importance as they shed a great deal of light on the structure of the phylum for paleontological purposes Suits of shells should be collected from each locality, and not just the most complete or most attractive of specimens. The collector must avoid being lured by pretty specimens away from the more rare specimens. Usually present, but harder to find, less common species are of great importance to the paleontologist and to you as a fossil collector. Yup, common and humble, but brachiopods deserve a lot of respect.