Aboral tubercles are always finer and more dense than oral tubercles. Tubercles are always perforate and typically crenulate, although a great deal of specialization in both spine and tubercle structure is found in this group. Spines are long and slender, and often have spatulate tips. Burrowing heart urchins have bands of very fine spines that are termed fascioles that help them live in fine sediments. The detailed shape and position of these fascioles is important taxonomically.
Heart urchins are deposit feeders using their oral tube-feet to gather detritus.