What are the similarities and differences between the Common Sea Urchin (Echinus esculentus), the Green Sea Urchin (Psammechinus miliaris or Strongylocentrotus droebachiensis), and the Purple Sea Urchin (Paracentrotus lividus or Strongylocentrotus purpuratus)?
The Common Sea Urchin, Green Sea Urchin, and Purple Sea Urchin are all spiny marine (saltwater) echinoderms in the Parechinidae family. Echinoderm means hedgehog skin.
The Common Sea Urchin, Green Sea Urchin, and Purple Sea Urchin are all spherical with short spines. They all have a hard shell called a test.
The Common Sea Urchin has varied-coloured spines, but mostly pinkish to brownish, whereas the Green Sea Urchin has greenish spines, and the Purple Sea Urchin has purple spines.
The Common Sea Urchin, Green Sea Urchin, and Purple Sea Urchin are all about the same size, ranging from 6-10 centimetres (2.5 – 4 inches) in diameter.
The Common Sea Urchin, Green Sea Urchin, and Purple Sea Urchin do not have eyes. They are sensitive to touch, light, and chemicals, due to the numerous sensitive cells in their spines, tube feet, and around their mouths.
The Common Sea Urchin, Green Sea Urchin, and Purple Sea Urchin can move, but very slowly. They crawl using thier tube feet. They have tubed feet in groups of five or six in a small arc shape.
The Common Sea Urchin, Green Sea Urchin, and Purple Sea Urchin are all benthic, which means that they live on the sea floor.
The Common Sea Urchin is found in all oceans, whereas the Green Sea Urchin is found in the Atlantic Ocean and the North Sea, and the Purple Sea Urchin is common in the Mediterranean Sea, the seas south of France, and in the eastern Atlantic Ocean.
Photographer: Martina Nicolls
Martina Nicolls: SIMILAR BUT DIFFERENT IN THE ANIMAL KINGDOM