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 keep the two halves aligned .
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 .