CORAL CLASSIFICATION II
There are four classes within the phylum Cnidaria:
- Class Scyphozoa
- Class Cubozoa
- Class Hydrozoa
- Class Anthozoa
The class Scyphozoa include the true jellyfish (figure 2-10), but do not contain corals.
Figure 2-10. a) Rhopilema sp. jellyfish; b) Moon jellyfish, Aurelia aurita
Photo Credits: a) Annelise Hagan; b) Rob Martimbeault
The class Cubozoa are the box jellyfish. They differ from Scyphozoans because they have a cube-like shape. This class also does not include corals.
The class Hydrozoa contains organisms such as hydroids, Portuguese man-of-wars, and some corals including fire corals and lace corals (figure 2-11).
Figure 2-11. a) Portuguese man-of-war, Physalia physalis; b) Distichopora sp. lace coral
Photo Credits: a) Felipe Cabeza; b) Pauline Bosserelle
Most corals are in the class Anthozoa, which also includes anemones. There are two main subclasses:
- Octocorallia (octocorals)
- Hexacorallia (hexacorals)
Now think back to math class: what does the prefix octo- mean? That’s right, eight. So octocorals means that corals in this class have eight-fold symmetry.
What type of symmetry do you think hexacorals have? That’s right, these corals have six-fold symmetry because the prefix hexa- means six.
Hexacorals and octocorals not only have different symmetry, but they also are very different from one another in structure. Hexacorals are hard or stony corals, meaning they secrete an outer skeleton composed of calcium carbonate (CaCO3). This is the same mineral that is in limestone (which is often composed of coral skeleton fragments; figure 2-12b).
Figure 2-12. a) Photo of a living mushroom coral; b) Calcium carbonate skeleton of a mushroom coral
Photo Credit: a) Alexandra Dempsey
Octocorals are soft corals (figure 2-13) and do not have a limestone structure. Instead, they secrete calcium or aragonite (minerals) sclerites. Sclerites are microscopic spicules (shards) that help to support the structure of the corals and anchor them to the substrate. Sclerites can be used to identify different species of soft corals.
Figure 2-13. Various octocorals
Photo Credits: a) Ken Marks; b) and c) Annelise Hagan
From this point on, the taxonomic classification of corals becomes more divided. Remember that there are over 1,000 species of corals worldwide. Please see the list of cnidarian taxonomy classified to suborder below.
Select Cnidarian Taxonomy
Domain – Eukarya
Kingdom – Animalia
Phylum – Cnidaria (anemones, corals, hydroids, jellyfish)
Class – Scyphozoa (true jellyfish)
Class – Cubozoa (box jellyfish)
Class – Hydrozoa (hydroids, Portuguese man-of-war, lace & fire corals)
Order – Stylasterina (lace corals)
Order – Milleporina (fire corals)
Class – Anthozoa (corals and anemones)
Subclass – Octocorallia (soft corals with 8-fold symmetry)
Order – Alcyonacea (soft corals)
Suborder – Calcaxonia (gorgonians)
Suborder – Holaxonia (gorgonians)
Suborder – Scleraxonia (gorgonians)
Suborder – Alcyoniina (true soft corals)
Suborder – Stolonifera (stolon corals)
Order – Helioporacea/Coenothecalia (blue corals)
Order – Pennatulacea (sea pens and sea pansies)
Subclass – Hexacorallia (hard corals with 6-fold symmetry)
Order – Scleractinia (stony corals)
Order – Actiniaria (sea anemones)
Order – Corallimorpharia (disc anemones)
Order – Zoanthidea (colonial anemones)
Subclass – Ceriantipatharia
Order – Antipatharia (black corals)
Order – Ceriantharia (tube anemones)