Phylum: Echinodermata
Class: Echinoidea
Order: Echinoida
Family: Strongylocentrotidae

Genus/species: Strongylocentrotus purpuratus

GENERAL CHARACTERISTIC: Round body with radially symmetrical test, (shell), covered with large spines 0.5 cm (2 in) in diameter, rarely to 10 cm (4 in). Test and spines are pale green (young) to purple (adults). Also covering the test or shell, are tube feet and pedicellariae (pincers). The long
suckered tube feet visible above the spines are used for locomotion and capture of food, which is then passed along to the mouth. The oral side of the urchin, on which the mouth is located, faces the substrate (down). Sexes are not physically distinguishable from one another (monomorphic).

DISTRIBUTION/HABITAT: British Columbia to Baja California in the lower intertidal to 160 m (525 ft) depth. Rounded burrows in rock that have been scoured out by the present or previous urchin using its teeth (Aristotle’s lantern) and spines, a strategy that protects from predators and surge.  Subtidal purple urchins live, often in large numbers, on the substrate among kelp holdfasts.


DIET IN THE WILD: Herbivore/Detritivore. Uses calcite (CaCO3) teeth (Aristotle’s lantern) to feed on kelp, other algae, diatoms and scavenge on dead animals. These urchins prefer the giant brown kelp Macrocystis and can destroy entire forests of kelp which are commercially important for fisheries. Algin a product from kelp is also used in the manufacturing of plastics, paints and as a thickening agent in foods such as gravy and pudding.

REPRODUCTION: Sexually mature during their second year. Sexes are separate, although hermaphrodites occur. Broadcast spawning deposits sperm or eggs into the sea where random fertilization occurs. Pluteus larvae hatch, drift and settle. Growth after metamorphosis is slow.

PREDATORS: Preyed upon by seastars such as the sunflower star and cancer crab species as well as fish such as the California sheepshead, shorebirds and sea otters. Sheephead blow over sea urchins and nibble at the oral side where the spines are shortest. When approached by most sea stars, the urchin allows the potential predator to get close, then uses its pincers to attack the sea star’s tube feet. Most sea star species will beat a hasty retreat; however, the sunflower star is too big and fast; the urchin cannot escape and is swallowed whole! Average lifespan 20 years but can live to more than 30 years.

CONSERVATION: CITES; no special status

REMARKS: Purple pigments from this urchin lodge in the bones and teeth of sea otters, turning the otter’s skeleton and teeth purple.

In the wild, they protect themselves from predation, drying out, and damage from the sun’s UV light by covering themselves with seaweed or shells.

Sea urchin is commonly used in sushi and is considered a delicacy Japan. The primary urchin harvesting company in California sends 75% of the harvest to Japan.


RockyReefcluster, Abalone and urchins, Rocky Coast Main Exhibit, Tidepool


California Academy of Sciences Docent Water is Life Guide 2015


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