Pencil urchins and heart urchins. Eucidaris is a genus of cidaroid sea urchins known as slate pencil urchins. The heart urchins or Spatangoida are an order of sea urchins. Sea urchins or urchins are small, spiny, globular animals that, with their close kin, such as sand dollars, constitute the class Echinoidea of the echinoderm phylum. Sea urchins move slowly, and feed on mostly algae. Sea otters, starfish, wolf eels, triggerfish, and other predators hunt and feed on sea urchins. Their roe is a delicacy in many cuisines. The name "urchin" is an old word for hedgehog, which sea urchins resemble. Undated, no illustrator credited.