Sea urchin
Sea urchins or urchins () are typically spiny, globular animals, echinoderms in the class Echinoidea. About 950 species live on the seabed, inhabiting all oceans and depth zones from the intertidal to . Their tests (hard shells) are round and spiny, typically from across. Sea urchins move slowly, crawling with their tube feet, and sometimes pushing themselves with their spines. They feed primarily on algae but also eat slow-moving or sessile animals. Their predators include sea otters, starfish, wolf eels, and triggerfish.
Arbacia punctulata
The Atlantic purple sea urchin is a spherical, dark purple-spined sea urchin, with a nearly flat oral face. It can reach up to 8 cm in diameter, and is native to the North Atlantic Ocean. 
Its natural habitat is in the western Atlantic Ocean. "A. punctulata" can be found in shallow water from Massachusetts to Cuba and the Yucatan Peninsula, from Texas to Florida in the Gulf of Mexico, the coast from Panama to French Guiana, and in the Lesser Antilles, usually on rocky, sandy, or shelly bottoms.