Book excerpt: Echinoderms play an important ecological role in marine communities, especially in relation to food chains, occupying diverse trophic levels such as herbivores, carnivores, detritivores and omnivores in the marine environment. These animals feed on many different kinds of food but the majority eat only small particles of edible matter suspended in the water or lying as detritus on the sea bottom. Although echinoderms occur at all depths from the intertidal to the abyssal zones and are present throughout all of the world's oceans, their distribution is limited by the composition and topography of the sea-bed, by temperature and pressure differences according to locality and depth, and by salinity and food supply. This book discusses echinoderms and their habitual environments as well as their reproductive biology and the ecology in which they form their habitats.