Corals are related to jellyfish and anemones.
On the surface, sponges and corals have a lot in common. The two just hang out there underwater, filtering out food particles, living in large colonies that provide habitats for other animals. Divers know that they come in many beautiful colors. But beneath the surface, these two organisms are completely different.
Sponges and corals come from different animal phyla, for example. Phyla is the most basic of all animal distinctions and refers to animals with completely different body plans. Sponges are among the simplest of all animals, lacking true tissues and deterring predators primarily through their lack of nutrition and shards of glass found in their bodies, called spicules. They are covered by small pores lined with cells equipped with flagella, which serve to circulate water through the sponge and absorb food particles. Sponges are capable of living anywhere in the ocean from the coast to 8,500 m (29,000 ft) deep or more. Sponges are members of the phylum Porifera and their alternative name is “poriferans”.
Most coral species live in the photic zone, which is the layer of the ocean that can still be penetrated by sunlight.
Corals are cnidarians, related to jellyfish and anemones. More complex than sponges, they have differentiated tissue and a true intestine. Corals look like isolated individuals, but are actually huge colonies made up of several genetically identical polyps just a few millimeters in diameter. These polyps have stinging tentacles, which is characteristic of cnidarians. Rather than relying on food particles for food, corals get much of their nutrition from symbiotic algae, which give them their color. Corals cannot live as deeply as sponges, most being found in the photic zone, where light can reach their algae, but some species are found at depths of 3,000 m (9,842 ft).
Sponges and corals are both members of very ancient lineages that probably split off from other animals 600 million years ago. Sponges were long thought to be the most basic of sponges and corals, but recent genetic studies have indicated that the ancestors of corals, the first cnidarians, actually split off from other animals first, and that sponges are likely of a lineage that was secondarily simplified.