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.
- links inside these captions for more info.
Hover over the main image to pause slideshow." title="entry3" width='170' height='135' />
- wall, septa and costae." title="slide3-1" width='170' height='135' />
- separate corallite walls." title="slide3-2-new" width='170' height='135' />
- obscure - the genus Pavona." title="slide3-3-new" width='170' height='135' />
- septa and costae (singular: septum and costa) in all their forms is critical to coral identification." title="slide3-4" width='170' height='135' />
- Septa are vertical skeletal elements inside the corallite wall, and are contiguous with costae when they cross over the wall. Costae may run across the coenosteum between corallites and join with the septa of the next corallite - the genus Favia." title="slide3-5" width='170' height='135' />
- septocostae - the genus Pavona." title="slide3-6" width='170' height='135' />
- ornament. Here a coral in the genus Lobophyllia shows large septal teeth. Underwater the presence of these teeth may be seen in the polyp's tissue." title="slide3-7-new" width='170' height='135' />
- Pali (singular palus) are vertical rods or blades that rise from the inner margin of the septa. Commonly known as paliform lobes they may form a visible crown that can be seen through the tissue underwater and are a useful aid in identifying the genus Goniastrea - pictured." title="slide3-8" width='170' height='135' />
- Axial corallites form the axis of growth at the tip of the branch and are "differentiated" from the surrounding radials (i.e they look different). The genus Acropora is defined by having axial corallites." title="slide3-9" width='170' height='135' />
- radial corallites (i.e. the corallite at the branch tip is not differentiated)." title="slide3-10-new" width='170' height='135' />
- axial furrow e.g. the genus Fungia shown here. In some genera (e.g. Ctenactis) the axial furrow may contain several mouths." title="slide3-11" width='170' height='135' />
- immersed corallites - the genus Porites." title="slide3-12-new" width='170' height='135' />
- exsert corallites. The genus Turbinaria, shown here, can have both exsert and immersed corallites." title="slide3-13-new" width='170' height='135' />
- irregular corallites - the genus Astreopora." title="slide3-14" width='170' height='135' />
- irregular (Echinophyllia - left) to neat and regular (Diploastrea - right)." title="slide3-15-new" width='170' height='135' />
- rounded (Montastrea - left) or polygonal (Leptastrea - right)." title="slide3-16" width='170' height='135' />
- inclined - the genus Mycedium." title="slide3-17" width='170' height='135' />
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)
- Veron, J. E. N. (2000). Corals of the World. Melbourne: Australian Institute of Marine Science.