Similar to all the sea urchin species they contain a circular hard shell (test) that bears many spines and the mouth, located at the bottom of the urchin which is comprised of calcareous plates that lead into the digestive tract (1). This species is also one of the most abundant and largest physically since they can grow up to a width of 18 cm and their coloration can be dark purple but some also have red spines as well (1). The red sea urchin is common along shallow waters and intertidal zones along the coast of California, including Baja California (1). The sea urchin diet consists of brown algae (kelp) remnants that are freely circulating and it is found that the feeding activity of the sea urchins increases within kelp forests (1). A decline in feeding is observed with increased distance from kelp forests since red sea urchins are selective for brown algae over red algae and food security for their preference is guaranteed in kelp forests (2).
(1) Kato, S., & Schroeter, S. C. (1985). Biology of the red sea urchin, Strongylocentrotus franciscanus, and its fishery in California. Mar. Fish. Rev, 47(3), 1-20.
(2)Mattison, J. E., Trent, J. D., Shanks, A. L., Akin, T. B., & Pearse, J. S. (1976). Movement and feeding activity of red sea urchins (Strongylocentrotus franciscanus) adjacent to a kelp forest. Marine Biology, 39, 25-30.