36 



OHIO FOSSILS 



Phylum Trochelminthes 



These are the "wheel-animalcules" or rotifers, common in fresh water and rare in the sea. 

 They have no fossil record in Ohio or elsewhere. The three "worm" phyla just mentioned are 

 very different from the segmented worms which belong to the phylum Annelida (see below). 



Phylum Bryozoa 



The moss-animals form colonies in which the individual is almost microscopic in size. 

 The colonies are usually small and attached to the sea bottom. Many bryozoans look like minia- 

 ture corals, from which they may be distinguished by the much smaller diameter of the tubes. 

 The animal is much more complex than the coral animal. Most of the bryozoans are marine but 

 there are a few freshwater forms; one of the latter builds globular colonies of huge size (up to 

 3 feet in diameter) but without calcareous skeleton. Most of the marine forms secrete calcar- 

 eous colonies which may be stemlike, leaflike, massive, or encrusting. The oldest known 

 bryozoans are late Cambrian in age and the phylum has survived to the present. 



The Paleozoic rocks of Ohio contain bryozoans in abundance. This is especially true of 

 the Ordovician rocks of the Cincinnati region and the Devonian rocks in both areas of outcrop 

 within the state. 



Phylum Brachiopoda 



hinge 



The brachiopods, or lamp shells, have a shell of two pieces, called valves. The two valves 

 are hinged together at one end and enclose the soft part of the animal. Brachiopods look a little 

 like clams, but they can easily be told apart by looking at the shells (fig. 34). In most brachio- 

 pods a line drawn from the pointed end, or beak, to the opposite 

 margin of the shell separates the valves into two halves that are 

 just alike. In a pelecypod shell the beak is nearer one end. In 

 most brachiopods one shell is thicker than the other and the beak 

 of one valve rides over the beak of the other. In some forms the 

 shell has a depression called a sinus which corresponds to a fold 

 on the opposite valve (see fig. 35). All brachiopods live in the sea. 

 They attach themselves to the bottom by means of a fleshy stalk, 

 called a pedicle, which grows out through a hole near the beak of 

 the shell. We find fossil brachiopods in rocks of all ages from the 

 Cambrian to the present time, and brachiopods are living in the 

 oceans of the world today. Judging by the fossils we have found, 

 there were more brachiopods during the Paleozoic than at any time 

 before or since. 



Fig. 34 



^*^ 



Fig. 35 



The brachiopods are divided into two classes, the Inarticulata in 

 which the valves are closed by muscles alone, and the Articulata in 

 which the valves are held together by muscles and various devices which 

 cause the shell to lock together. 



Both classes of brachiopods are abundant in the Paleozoic rocks 

 of Ohio but the articulates are by far the most numerous. 



Phylum Mollusca 



GENERAL. This phylum includes the clams, snails, devilfish, 

 squids, octopus, and related animals. The Mollusca have a soft body, 

 enclosed in a fleshy mantle, and move about by means of a foot; the 

 animal is commonly enclosed in a solid, limy shell. The phylum con- 

 tains five classes of which two, the Aanphineura (chitons or coat- of- 



