Explanation:

Purple Urchins are known as 'Cockroaches of the Ocean'. 

The purple sea urchin, Strongylocentrotus purpuratus, lives along the eastern edge of the Pacific Ocean extending from Ensenada, Mexico to British Columbia, Canada.

"Cockroaches of the sea" is an expression of unknown origin that traditionally refers to lobsters. The bottom-feeding crustaceans, generally the blue American lobsters, have long been a staple in the North American diet, possessing a nutritious and rich flavor without the extra calories. Lobsters weren't always the exquisite delicacy of five-star restaurants, though, and were once as common as cockroaches. Nowadays, "cockroaches of the sea" has come to represent a variety of creatures from the ocean.