Different Types of Coral Species

Corals are sessile marine animals meaning they do not move and live in saltwater environments, respectively. They belong to the class Anthozoa, a class of marine invertebrates known as cnidarians. This makes them relatives of jellyfish. Unlike jellyfish, coral lack the free-living adult medusa phase. They only remain in the polyp phase attached to the ground and without the ability to move

Despite this immovability, corals have very interesting characteristics which allow them to adapt well to their marine environments. All corals are colonial, being made up of hundreds of individual polyps that are responsible for feeding and reproducing the colony. This is the case with coral reefs which become important ecosystems of their own.

Coral reefs are particularly important for marine ecosystems. This is because they provide food and shelter for various animal life. For example, certain fish can hide in coral to surprise their prey. Coral reefs also play important roles in protecting coastlines from storms and erosion.

Although they often look like plants, corals are animals. The long parts which rise upwards like branches are actually tentacles. They also have other body parts such as mouths and stomachs. Some can feed on algae or other plant matter, but many can also catch prey with their tentacles. Corals can also produce both sexually or asexually, depending on circumstances.

Now we know about coral species in general, we can look at the first main type of corals. The following are characteristics of stony corals, also known as hard corals.

• Stony corals are corals that secrete a skeleton of calcium carbonate, which is why they are also known as true corals.
  
  
• Immersed in this skeleton are the individual polyps that form the colony. They are responsible for capturing food by moving the plankton with their tentacles towards the inside of their mouth. They ingest these minute organisms and digest them to use their nutrients.
  
  
• In addition to this heterotrophic feeding route, a large part of the stony coral species have symbiotic zooxanthellae algae within their polyps. They can use these to exchange nutrients for mutual benefit. Those that have this symbiotic relationship with these organisms obtain most of their nutrients from this pathway. Learn more about this process with our article on what are zooxanthellae?
  
  
• To defend themselves, polyps can retract into their calcareous skeleton, which is like a cage that gives them shelter.
  
  
• When these corals die, the entire skeleton remains. You can still see the cells of each polyp and the septa that make it up.
  
  
• These are the corals responsible for building marine reefs. These are a stone formations that give structure to the ecosystem.
  
  
• They can be easily confused with rocks or hard plants, but they are really living animals.
  
  
• These coral reefs are very important for marine biodiversity, because they are home to 25% of marine species. They function as refuges and nurseries for hundreds of species, having a very important value in productivity and marine richness.

Types of stony or hard corals

The stony corals belong to the subclass Hexacorallia, commonly called hexacorals. They are characterized by the the polyps having 6-sided symmetry. This can be observed in the gastrovascular cavity that is divided into multiples of 6 and are completely smooth without branches. This subclass includes stony corals, zoanthids, corallimorphs and anemones, but stony corals are those under the order Scleractinia.

Some example types of stony corals include the following:

• Staghorn coral (Acropora cervicornis)
• Elkhorn coral (Acropora palmata)
• Mustard hill coral (Porites astreoides)
• Plating montipora coral (Montipora capricornis)
• Moon coral (Favia speciosa)
• Cauliflower coral (Pocillopora damicornis)
• Maze coral (Diploastrea heliopora)
• Bird's nest coral (Seriatopora hystrix)
• Flowerpot coral (Goniopora stokesi)
• Horn coral (Hydnophora microconos)

You can learn about an organism that has the same common name, but which is actually not technically a coral, with our article on what is fire coral?

We have explained the characteristics of soft corals and we now do the same for soft corals:

• Soft corals do not have a calcareous skeleton. For this reason, they have a consistency and less protection from the elements and other animals.
  
  
• Solitary polyps are arranged around this soft tissue, which together form the colony.
  
  
• They have spicules arranged within this soft tissue. These are structures of calcium carbonate crystallized in calcite that provide support and defense against predators. These spicules are very useful when identifying species, because there is a great variety in shapes and sizes.
  
  
• In addition to this physical defense, many species have chemical defense toxins to secrete as protection.
  
  
• These corals do not look like rocks like stone corals, but are more reminiscent of plants .
  
  
• Although they do not build marine reefs, they are part of them. They help to give structure to the reef, in addition to contributing to ecosystem wealth and balance.
  
  
• They also obtain their food by capturing plankton with their tentacles and many species can have symbioses with zooxanthellae.
  
  
• They can thrive better than stony corals in lower light conditions.

Types of soft corals

Soft corals are within the subclass Octocorallia, with polyps characterized by having 8 branched or pinnate tentacles. Their gastrovascular cavity is divided into 8 septa. Under this class, the orders that contain soft corals are mainly the Alcyonacea. Exceptions are the family Tubiporidae and the order Helioporacea. Among the soft corals we can find cnidarians of the order Pennatulacea, commonly known as sea pens.

There is a special case of soft coral known as sea fans and sea whips. They have a relatively hard horny skeleton that is made of a protein called gorgonin that gives it a flexible but rigid single-axis consistency. It is not strictly rigid because it does not secrete a calcium carbonate skeleton, but it is not soft like its close relatives.

Depending on whether it is phylogenetic origin, it the ability to form reefs or the hardness of the tissue, it can be classified as soft coral or stony coral. Given this, a new special category has been created to group them as types of gorgonian corals.

Some examples of soft coral species include the following:

• Toadstool coral (Sarcophyton spp.)
• Leather coral (Sarcophyton spp.)
• Devil's hand coral (Lobophytum spp.)
• Kenya tree coral (Capnella spp.)
• Pulse coral (Xenia spp.)
• Colt coral (Cladiella spp.)
• Sinularia spp.
• Nepthea spp.
• Finger leather coral (Alcyonium spp.)
• Cabbage leather coral (Sinularia spp.)

Learn more about these different types of coral species with our article on what are considered soft corals?

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