Stalactite sponge

Clathrina clathrus forms delicate yellow-white lattice networks across the cave ceiling and stalactite surfaces, thriving in the total absence of light and algae competition that characterises the inner chamber. As a calcareous sponge it builds its skeleton from calcium carbonate spicules, a rare trait among Mediterranean sponges and one that gives the colonies a faintly crystalline appearance under dive lights. Dense cave populations of Clathrina indicate stable, cool, low-nutrient water conditions — the same factors that have preserved the stalactite formations above them.