millepore, (Millepora), any of a genus of invertebrate marine animals comprising the order Milleporina (phylum Cnidaria). Millepores are common in shallow tropical seas to depths of 30 metres (about 100 feet). Unlike the true corals, which belong to the class Anthozoa, millepores are closely related to the hydra (q.v.). Both hydras and the millepores belong to the class Hydrozoa. Some species form branching treelike growths up to 50 centimetres (about 20 inches) high. Others form massive and shapeless or leaflike growths. Most are whitish, yellowish, or beige in colour. As with other cnidarians, they bear powerful stinging structures called nematocysts, which are used for defense and for capturing food.