Appendix. Colophon

The animals on the cover of Asterisk: The Definitive Guide are starfish (Asteroidea), a group of echinoderms (spiny-skinned invertebrates found only in the sea). Most starfish have fivefold radial symmetry (arms or rays branching from a central body disc in multiples of five), though some species have four or nine arms. There are over 1,500 species of starfish.

Starfish live on the floor of the sea and in tidal pools, clinging to rocks and moving (slowly) using a water-based vascular system to manipulate hundreds of tiny, tube-like legs, called podia. A small bulb or ampulla at the top of the tube contracts, expelling water and expanding the starfish’s leg. The ampulla relaxes, and the leg retracts. At the tip of each leg is a suction cup that allows the starfish to pry open clam, oyster, or mussel shells. Starfish are carnivores; they eat coral, fish, and snails, as well as bivalves.