Two major groups are recognized, articulate and inarticulate. Articulate brachiopods have toothed hinges and simple opening and closing muscles, while inarticulate brachiopods have untoothed hinges and a more complex system of muscles used to fit the two halves together. In a typical brachiopod a stalk-like pedicle goes from an opening in one of the valves (the pedicle valve). It attaches the animal to the seabed but clear of silt that would block the opening.