Cape sea urchins (Parechinus angulosus) provide important nurseries for abalone (perlemoen). The spines of the urchins protect juvenile abalone from predators such as octopus, klipfish and rock lobsters. The dramatic disappearance of these urchins has left juvenile abalone in the open, making them an easy target for hungry predators.
Sea urchins move by increasing or decreasing the amount of water in it’s water vascular system thus allowing it to extend or contract its feet. The foot extension and contraction enables it to move about the water.
Conceived in the open sea, tiny spaceship-shaped sea urchin larvae search the vast ocean to find a home. After this incredible odyssey, they undergo one of the most remarkable transformations in nature.
Sea urchins reproduce by sending clouds of eggs and sperm into the water. Millions of larvae are formed, but only a handful make it back to the shoreline to grow into adults.
Sea urchins are spiny invertebrate animals. Adult sea urchins are globe-shaped and show five-point radial symmetry. They move using a system of tube feet. Sea urchins belong to the phylum Echinodermata along with their relatives the sea stars (starfish), sand dollars and sea slugs.
Male sea urchins release clouds of sperm and females release huge numbers of eggs directly into the ocean water. The gametes meet and the sperm fertilize the eggs. The fertilized eggs grow into free-swimming embryos which themselves develop into larvae called plutei. The plutei swim through the ocean as plankton until they drop to the seafloor and metamorphosize into the globe-shaped adult urchins.