Strongylocentrotus franciscanus, commonly called the red sea urchin (although its color ranges from pink or orange to nearly black), is a sea urchin found in the Pacific Ocean from Alaska to Baja California. It lives in shallow waters from the low-tide line to 90 metres (300 ft) deep, and is typically found on rocky shores that are sheltered from extreme wave action.^{[citation needed]}

Physical description

Strongylocentrotus franciscanus juvenile, found at Cape Flattery, WA. This individual is about 1.5 cm in diameter.

A sea urchin's spherical body is completely covered by sharp spines that can grow up to 8 cm (3.1 in). These spines grow on a hard shell called the "test", which encloses the animal. The oldest ones have been measured to be around 19 cm (7.5 in) in diameter. It can vary in color from red to dark burgundy. Rarely, albino specimens are found. A sea urchin has no visible eyes or legs. It has a mouth located on its underside, which is surrounded by five teeth. During larval development, the body of a sea urchin transitions from radial to bilateral symmetry.

This bilaterally symmetrical larva, called an echinopluteus, subsequently develops a type of pentaradiate symmetry that characterises echinoderms. It crawls very slowly over the sea bottom using its spines as stilts, with the help of its tube feet. Scattered among its spines are rows of tiny tube feet with suckers that help it to move and stick to the sea floor.

Feeding habits

The animals have a mouth with special jaws (Aristotle's lantern) located on the bottom (oral) surface. Their preferred diet is seaweeds, kelp and algae, which they scrape off and tear up from the sea floor. During larval development, urchins use bands of cilia to capture food from the water column.^[1] Red sea urchins found in the channel adjacent to San Juan Island have been found to live a uniquely sedentary lifestyle with the heavy currents bringing an abundance of food.^[2]

Behavior and reproduction

Sea urchins are often found living in clumps from five to ten. They have the ability to regenerate lost spines. Lifespan often exceeds 30 years, and scientists have found some specimens to be over 200 years old.^[3]

Spawning peaks between June and September. Eggs are fertilized externally while they float in the ocean, and planktonic larvae (echinopluteus) remain in the water column for about a month before settling on the bottom of the sea floor, where they undergo metamorphosis into juvenile urchins. These juveniles use chemical cues to locate adults. Although juveniles are found almost exclusively under aggregated adults, the adults and juveniles are not directly related. Red Sea Urchins can effectively reproduce at an advanced age.^{[citation needed]}

References