Purple urchins
Purple urchins, or Strongylocentrotus purpuratus, live in tidepools along the West Coast of North America.
Urchin spines
The urchin's spines help it skewer food and protect itself against predators.
Spawning female urchin
The urchins breed annually around January, February and March.
Urchin larva
The urchins start out as free-floating larvae that may swim and feed for several months.
Urchin metamorphs
Urchins undergo metamorphosis from a larval form to an adult form.
Inside-out urchin
Sea urchin larvae turn inside-out as the larvae metamorphose to adults.
Sea urchin genome
Scientists recently sequenced the genome of the purple sea urchin.