Brachiopod:
Platystrophia

These clam-like filter feeders are common fossils in Ordovician deposits.

Platystrophia appears in many different sizes and species

Bivalve Mollusk:
Byssonychia radiata

The image abive shows an external mold of Byssonychia

Although bivalaves and brachiopods have similar appearances, they belong to different animal phylums.

Bivalves and Gastropods (including modern snails) belong to Mollusca.

Bryzoans -- "moss animals" pictured below and on the far right -- are in a third phylum.