Brain Coral Skeleton

Brain Coral Skeleton – What’s Inside?

Brain coral is one of the most identifiable corals in the world. Their distinct wrinkly exterior is commonly recognized, but what is actually inside of a brain coral?

Underneath those wrinkles, brain corals actually have a skeleton, mouth, and reproductive system. However, despite their name, they do not have a brain.

There is a lot more to brain coral than meets the eye. Read on to learn more about what is inside of brain coral, as well as answers to some common myths about brain coral.

What is Inside Brain Coral?

There is a lot more to brain coral than meets the eye. Despite their fairly simple appearance, brain coral contains multiple internal systems and organs, including the following:

  • Skeleton
  • Reproductive system
  • Tentacles
  • Mouth

Some parts of the brain coral are straightforward, such as using its mouth to eat food. However, other parts, such as the tentacles and mouth, are confusing at first glance. Brain coral do not have appendages and their internal systems function slightly differently to our own.

The biggest difference is that brain coral is actually made of a colony of polyps that share one skeleton. The polyps work together to build the skeleton, obtain food, and provide a home for certain algae, which in turn gives the brain coral oxygen. Essentially, the polyps are what makes and sustains life for brain coral.

Coral Polyps and Algae

A coral polyp is a soft tissue small invertebrate that has a sac shaped body and a mouth encircled by stinging tentacles. They live together as a colony and work together to share nutrients, hormones, and oxygen. However, if one polyp becomes sick, it is extremely easy for the illness to spread throughout the entire colony.

The tissue of a coral polyp is home to an algae called zooxanthellae, which gives brain coral its coloration, ranging from brown or yellow to a greenish tint. If temperatures get too high, the coral will expel the zooxanthellae, which exposes the coral’s skeleton. If temperatures return to normal, the algae will return. However, when the algae is gone, the coral will be quite stressed and can even die.

The Skeleton

Coral polyps use calcium carbonate from seawater to build a hard, cup-shape skeleton. Over time, the skeleton will continue to grow. The skeleton itself is attached to the bedrock of the ocean floor and gives brain coral its distinct ridges. It is also the only part of brain coral that can be fossilized when a brain coral dies.

The Reproductive System

Surprisingly, the reproductive system of brain coral is relatively straightforward. Brain coral has eggs and sperm, which are fertilized to create new brain coral. However, unlike humans, brain coral can reproduce asexually as well. They also do not have appendages for sexual reproduction.

The Tentacles

Brain coral do not have tentacles in the traditional sense, like a squid or octopus. The tentacles on brain coral are quite tiny and live in the grooved ridges of the brain coral. Their main purpose is to help guide food to the mouth.

The tentacles can be retracted if the brain coral feels threatened. This ensures that the tentacles cannot be eaten. Typically, brain coral will extend the tentacles at night to catch food and retract them during the day.

The Mouth

Brain coral are filter feeders. This means that they catch small organisms that drift by them in the ocean, such as zooplankton. The tentacles will guide these organisms to the mouth, which is actually just an opening. Brain coral do not chew and swallow like we do.

The purpose of the mouth is to consume food to give the brain coral energy. It also helps provide the algae living on the coral with necessary nutrients so the algae can generate more food for the coral. The coral polyps and algae have a symbiotic relationship and will give each other nutrients continuously.

Does Brain Coral Actually Have a Brain?

Surprisingly, brain coral does not have a brain. Instead, brain coral has a nervous system known as a nerve net. The nervous system extends from the mouth to the tentacles. This allows the polyps to detect certain substances, such as sugars, and to detect prey.

Is Brain Coral a Hermaphrodite?

Brain coral is a zooxanthellate coral, most of which are hermaphrodites. This means that they can produce both eggs and sperm. However, they do not have any exterior genitalia, which means the process of reproduction is a little complicated and unusual.

How Does Brain Coral Reproduce?

Brain coral can reproduce asexually and sexually. During asexual reproduction, new polyps will bud off from the skeleton and begin a new colony of polyps, forming a new brain coral. Asexual reproduction occurs when the brain coral reaches a certain size and divides. Brain coral will asexually reproduce multiple times throughout its life.

For sexual reproduction, brain coral will either fertilize larvae within the body of the polyps or release many eggs and sperm into the water. This allows the brain coral to distribute their offspring over a broad area. The eggs and sperm will eventually join to create a free-floating larvae. Eventually, the larvae will settle and become polyps and form new brain corals.

Is Brain Coral a Fossil?

Due to the fact that brain coral is made up of thousands of living polyps, brain coral is not a fossil. However, brain coral can become a fossil. Like many other species, once brain coral dies, its skeleton is left behind and can become fossilized.

Brain Corals Fossils

The calcium carbonate skeleton of brain coral is what gets preserved as a fossil. Brain coral can live for up to 900 years, so there are not many brain coral fossils. The fossilization process for brain coral can take up to 20 million years to complete.

Fossilized brain coral is typically found in fragments. Sometimes small patches of complete brain coral fossil are found still attached to the bedrock of the ocean floor. The fossils are quite tough and have a white and waxy appearance. The iconic wrinkles of brain coral are still present in the fossilized skeleton, making it easy to identify.


Brain coral are made of polyps that form a colony and are home to zooxanthellae algae, which share a symbiotic relationship by providing each other with nutrients. Though it may not look like it, brain coral has a skeleton, tentacles, mouth, and both male and female reproductive systems. They may not a brain, despite their name, but they are still quite complex.