Key Features Pack of 3 Different sized Urchins Adds interest and colour to the tank Easy to add to any aquarium Pack of 3 White Sea Urchins Largest of the 3 is 6cm New to the Oase BiOrb range are the realistic and fun looking Sea Urchins. Available in white this pack of 3 small ornaments can be added to any Biorb or fish tank display to add interest and a decorative look. The ornaments can be placed around the base of the display to blend in with any pebbles or ornaments. All decorations should be rinsed prior to placing in a tank.