Brachiopods: A Sea Shell with a Foot?
Brachiopods are invertebrate animals that contain two shells held together by muscular tissue. They seem like clams on the surface but have some very distinct features that distinguish them from the mollusks altogether and place them in their own phylum, Brachiopoda. The most important differences exist in the soft tissue, but brachiopod shells tell us a great deal as well. The first, most obvious difference, is that in clams the shell is symmetrical parallel to its opening while in brachiopod shells are symmetrical perpendicular to their opening. Another feature characteristic to brachiopods is the presence of a dinstinct anchorning mechanism called a pedicle. This pedicle is anchored directly to the shell of the brachiopod and projects through an opening in the posterior and will attach to hard substrates. This serves as a holdfast to keep animals anchored to the ground in high energy environments.