Thursday, August 24, 2017

Corals as Individuals – The Corallite

The individual coral animal is called the polyp.  This simple sac-like animal sits in a skeleton cup made of calcium carbonate, called a corallite.  Together the tissue and the skeleton are called the corallum or coralla (plural).  The following article discusses the key terms relating to the corallite, which you will need to understand to identify corals and negotiate the literature.  For information on the polyp read the Coral Basics – The Polyp article.

Using Corallite Characteristics to ID Corals

As with any aspect of coral morphology, it is unwise to rely on any one characteristic when identifying a coral.  But reviewing predominant corallite characteristics is a useful step on the identification pathway.  Below are two examples of how knowledge of corallite structures can help with identification:

Ctenactis vs. Herpolitha

Both of these genera are free-living elongate discs, but the septal structures are significantly different allowing easy identification.  The septa of Ctenactis (p. 24 of the Coral Finder) run continuously from the centre of the disc to the edge and have regular blade-like teeth.  Whereas the septa of Herpolitha (p. 25 of the Coral Finder) form a messy discontinuous pattern heading out towards the colony edge, and the teeth are considerably smaller than those of Ctenactis.

(Photos of ctenactis and herpolitha close up to show septa)

Echinophyllia vs. Mycedium

The corallites of Echinophyllia and Mycedium are similar in size (5-15mm) and shape, and grow in thin plating colonies.  Furthermore the colony surfaces may look extremely alike.  But these genera are easily separated by looking at the orientation of the corallites.  Mycedium has corallites that are inclined towards the colony margin forming nose-shaped structures.  The corallites of Echinophyllia are somewhat irregular in orientation but they are clearly not all angled to the edges of the colony.  Once again small but clear differences allow for simplified coral identification.

(Photos of echinophyllia and mycedium showing corallite orientation)

Learning Resources


Suggested Reading

  • Veron, J. E. N. (2000). Corals of the World. Melbourne: Australian Institute of Marine Science.