Brachiopod

Brachiopods, phylum Brachiopoda, are animals with hard valves, or shells, on their upper and lower surfaces, unlike the left-and-right arrangement of bivalve molluscs. Their shells are hinged at the rear and can be opened at the front for feeding or closed for protection; two main groups exist, articulate forms with toothed hinges and inarticulate forms with weaker, untoothed hinges. Most living brachiopods are marine, favoring cold water and low light, and around 400 species survive today, a small remnant of the phylum's former dominance during the Paleozoic.