AlcyonariaOctocorallia

Alcyonaria, also known as soft corals, are a subclass of Anthozoa, a class within the phylum Cnidaria. They are marine invertebrates that, unlike their stony coral relatives, do not secrete a rigid external skeleton. Instead, alcyonarians possess an internal skeleton composed of spicules made of calcium carbonate, which can vary in shape and size. This spicular skeleton provides them with structural support.

Alcyonarians are characterized by having eight pinnately branched tentacles. They typically exist as colonial organisms, with numerous individual polyps interconnected by a common tissue called a coenenchyme. Each polyp has a gastrovascular cavity that is divided into eight mesenteries. Reproduction can be both sexual and asexual, with many species exhibiting broadcast spawning.

This subclass includes a diverse array of organisms such as sea fans, sea whips, and true soft corals. They are found in marine environments worldwide, from shallow coastal waters to the deep sea, and play important roles in reef ecosystems by providing habitat and food for other organisms. Their lack of a massive external skeleton makes them more flexible and often less brightly colored than stony corals, though some species can be vibrant. Many alcyonarians contain symbiotic algae called zooxanthellae, which contribute to their nutrition through photosynthesis.