Milleporids

Milleporids are a genus of hydrozoans, which are marine invertebrates belonging to the phylum Cnidaria. Commonly known as fire corals, milleporids are colonial animals that superficially resemble stony corals, but are distinct in their biology and skeletal structure. They secrete a hard, calcium carbonate skeleton that forms the branching or encrusting structures characteristic of their colonies. These colonies can grow to considerable size and are important reef-builders in tropical and subtropical waters.

The name "fire coral" derives from the stinging cells, or nematocysts, found on their tentacles and surface. These nematocysts can deliver a painful sting to humans upon contact, causing a burning sensation, rash, and itching. The potency of the sting varies among species. Milleporids are carnivorous, feeding on small planktonic organisms captured by their tentacles. They are found in a wide range of marine environments, from shallow reefs to deeper waters, and are a significant component of many coral reef ecosystems. Reproduction in milleporids is complex, involving both sexual and asexual phases. They are often a food source for certain marine animals, such as nudibranchs and parrotfish, which have adaptations to tolerate or avoid their stinging cells.