The beautiful coral reefs you see underwater are actually animals and not plants!
Coral is any structure that is made up of hundreds of thousands of tiny coral creatures called polyps. They are translucent animals of a sessile nature, which attach themselves to the ocean floor, ‘taking roots’ just like plants.
But, How?
The major differentiating factor between plants and animals is that plants can produce their own food through photosynthesis while animals have to rely on food sources.
The basic structural material of plants is polysaccharide such as cellulose and they lack muscle, nerves and digestive tissues. On the other hand, animals necessarily have muscle, nerves and digestive tissues and their basic structural material is minerals, protein and a polysaccharide such as chitin but never cellulose. This all makes corals more of animals than plants.
What do they eat?
Corals are animals with a have tiny, tentacle-like arms that they use to capture their food from the water and sweep into their inscrutable mouths. Therefore, they have a means to collect food, they have a large percentage of their body devoted to capturing their prey. Their external skeleton comprises of protein and calcium carbonate.
Though, reef building corals do contain algal cells that photosynthesize, producing sugar and other chemicals. However, all reef corals require additional sources of nutrition, are most active predators and must feed. Most corals are not reef building and are found as individual polyps in deep water, lacking the symbiotic algae and are incapable of photosynthesis.
Reproduction
Corals are typically capable of reproduction with sexual and asexual phases, but these are not comparable to the gametophyte and sporophyte generations of plants. Unlike most plants, all corals are capable of locomotion at some stage in their life cycle, typically as a swimming dispersal stage called a planula larvae. Note that plants lack larvae.
Corals have nerve tissues as they are highly capable of sensing the environment. They also have the ability to move, hence they have muscle tissue as well.
They surely know how to defend themselves
An Anemone Swims Away From Sea Star