The average life span of sea urchins reaching adulthood is seven to 20 years, depending on species and habitat, and there are roughly 700 species worldwide. Red sea urchins, one of the oldest living animals on Earth, may reach 100 to 200 years of age.
Most sea urchins produce several million eggs, of which only a small percentage are fertilized. Due to predation by crabs, sunflower stars, sea otters, snails, birds and fish, an even smaller percentage survive from their plankton-like form to adulthood.
Juvenile sea urchins may take several months to form; the period from fertilization to reproductive adult ranges from two to five years.