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’.