1 In brachiopods (Brachiopoda), a pair of feathery structures forming part of the lophophore. The brachia are twisted up within the shell in various ways and serve to filter food particles from the water.
2 In crinoids (Crinoidea), long, plated, flexible arms made up of a series of articulated ossicles containing a water vessel from which the tube-feet arise. When feeding the tube-feet are extended; at other times they are covered by ‘brachial plates’. Small arms coming from the main brachia are called ‘pinnules’ and are made up of ‘pinnular plates’.