There is very little spine and tubercle differentiation in comparison to spatangoids. Tubercles are preforate and crenulate. In most sand-dollars there are five grooves radiating from the peristome, and these may branch many times to form an intricate pattern of food grooves . These are lined with tube-feet and are used to transport food particles to the central mouth. Another prominent feature of some sand dollars are slit-like perforations termed lunules .
Sand dollars have both a lantern and a perignathic girdle.
The lantern is unusual in being highly flattened and lacking compasses. The perignathic girdle may be made up of single interambulacral processes, or paired ambulacral processes. Cassiduloids have neither a lantern nor a perignathic girdle as adults, although a lantern is present in early development and is later resorbed. In clypeasteroids the upper and lower surfaces of the test are connected by an often extensive series of buttresses and pillars. These are purely structural and reinforce the test.