Clathrina clathrus is a species of calcareous sponge belonging to the Clathrinidae family. It is a shallow-water species of the Mediterranean Sea and is also found along the Atlantic coasts of Europe as far north as the British Isles.
This sponge is yellowish or white and grows up to 4 inches in diameter. It usually appears cushion-shaped at a distance — its close relative Clathrina coriacea is appears more flattened. Upon closer inspection, the sponge is actually a tangled mass of tubes. These tubes are thicker and less tightly knit than in C. coriacea. Its spicules are exclusively three-pointed triactines.
Image Caption: Clathrina clathrus. Credit: Elapied/Wikipedia(CC BY-SA 2.0)