corals: some common shapes & textures
updated Nov 11
species is tricky and requires experience and expertise. Many different
aspects of the coral are considered in working towards an identity.
These include the overall colony shape, the shape and arrangement
of the corallite, the structure of the corallite (scroll to bottom
of this page for more), especially the small structures (which often
require microscopic examination of a dead specimen - it's hard to
see these structures in a live coral as the tissue covers them), in
some the shape of the polyp too. The geographical location and depth
at which the coral was found also helps.
It is very difficult to accurately identify corals to species from
just a photograph.
Can we tell the species of corals from their
overall shapes? The overall shape of a colony can be affected
by the stresses it faces, e.g., waves, damage, disease. Thus, the
same species of hard coral may take on different shapes depending
on where the colony grows, e.g., shallow water, deeper water, exposed
to waves or sheltered waters. There are also geographical variations.
Also, a single colony of hard coral may have a combination of shapes.
Some, for example, may form an encrusting layer with some portions
of the colony rising up in columns or branches.
Some common shapes of hard coral colonies include the following described
Corals can take on a wide variety of shape.
Raffles Lighthouse, Jul 06
or crustose: a layer stuck to a hard surface, often growing
to follow the contours of the surface. Many corals have an encrusting
base from which other growth forms emerge, e.g., columns or branches.
(Columnar): forming thick unbranched columns usually from a
common solid base (i.e., thicker than branching corals, usually
with blunt tips as opposed to sharper tips of branching forms).
Such shapes are usually found in mid-depth water sheltered from
extreme water flow.
(Laminar): forming a thin horizontal plate, sometimes in tiers
or terraces of plates. Some may be folded into ruffles or have columns
or knobs arising from the plates.
plate-like colonies can form a vase-like or cone shape. Such shapes
are usually found in sheltered, mid-water depths.
(Folicaeous): forming thin plates that are often folded into
shapes that resemble leaves or petals of a rose, or a head of lettuce.
Such shapes are usually found in areas with turbulent water flow.
The surface patterns
on hard corals are a result of the shape of the corallites and the way the
common surface patterns on hard coral colonies include:
each corallite is distinct and has its own walls. Each corallite
is long and tubular resulting in corallites that look like trumpets.
These long corallites may be arranged to result in a spherical-looking
colony, especially when the polyp tentacles are extended and obscure
Other surface patterns
on hard corals may result from patterns on the skeleton between the corallites
(coenosteum). Other identification details include the shape of polyps and
tissues covering the skeleton.
*Species are difficult
to positively identify without close examination.
On this website, they are grouped by external features for convenience of
of a corallite
Reproduced from Corals
of the World Australian Institute of Marine Science,
Veron, JEN and Stafford-Smith, MG (2011)
The skeleton of an individual polyp, called the corallite, is a
tube that contains vertical plates radiating from the centre. The
tube itself is the corallite wall and the plates are the septo-costae.
The tubes are joined together by horizontal plates and other structures,
collectively called the coenosteum. Some polyps have an additional
thin film of skeleton around the wall called the epitheca. The wall
is formed by five skeletal elements which vary in proportion in
different coral families and/or genera. These elements are (a) septo-costae
(which become thickened within the wall), (b) coenosteum (which
forms a sponge-like structure), (c) synapticulae (which are horizontal
rods forming a lattice between the septo-costae), (d) sterome (which
form a non-porous layer within the wall) and (e) epitheca (which
forms a thin non-porous layer on the outside of the wall). The wall
is very prominent in some corals, but is inconspicuous in others
where individual polyps are indistinct.
are the radial elements of the corallite and are divided (by the
wall) into two components: the septa, which are inside the wall
and the costae, which are outside the wall. Where the wall is indistinct
(as in the Siderastreidae, Agariciidae and colonial fungiids) the
septo-costae are single uniform elements. In solitary fungiids the
wall is horizontally compressed, with the septa above it and the
costae below it. In most corals, the septa are of different lengths
and have a cyclical symmetry. They may be in cycles (usually with
6 septa in the 1st cycle, 6 in the 2nd cycle, 12 in the 3rd, 24
in the 4th and so-on if present) or orders (where there is an indeterminate
number of septa of each length). In practice, this cyclical arrangement
is often unclear. In many corals, but especially in Dendrophylliidae,
the cyclical arrangement of septa is embellished into a pattern
of fusion called pourtales plan, where septa or the 4th cycle curve
in front of those of the 3rd cycle and fuse. This appears to be
a primitive characteristic of the Scleractinia as it sporadically
occurs in several families and can also be seen in the earliest
fossils. The genus Porites has a unique septal plan which is used
extensively in taxonomy.
Septa seldom join at the centre of the corallite (except in the
Astrocoeniidae and Pocilloporidae). Instead, their inner margins
usually have fine inward-projecting teeth which, in most corals,
become intertwined forming a tangle called the columella. In some
families, especially the Astrocoeniidae and Pocilloporidae, the
columella is pillar- or dome-shaped. In others, especially the Acroporidae,
it is usually absent. Many corals have pillar-like projections on
the inner margin of some or all of their septa called paliform lobes
and these often form a neat circle around the columella called a
paliform crown. Some groups of corals have pali instead of paliform
lobes. These are the result of the pourtales plan pattern of septal
fusion although the pattern may not be visible in mature corallites.
There are four other parts of the skeleton which are used in general
descriptions of corals (apart from being components of corallite
walls as noted above): coenosteum, sterome, dissepiments and epitheca.
The coenosteum is a general term for porous (not solid) skeletal
material situated between the costae of corallites or between one
corallite and the next. This is best seen in the Dendrophylliidae
where the corallite wall and the skeleton between the corallites
consist of a sponge-like matrix of coenosteum. The sterome is a
solid sheet which forms the inner lining of (or all of) the corallite
wall. This is best seen in families Euphyllidae, Oculinidae and
Meandrinidae and gives the skeleton a porcelain-like finish. The
dissepiments are thin, blister-like layers of skeleton which form
between the corallites and are structurally similar to the sterome.
The epitheca is a delicate translucent skeletal layer. It initially
occurs as the basal plate deposited by the planula larva on settlement,
and thereafter may continue growing to envelop individual corallites.
The epitheca is always a distinct skeletal entity which is not covered
by living tissue; in some faviids its growth is controlled by tiny
polychaete worms to form 'groove-and-tubercle' structures.
- Veron, Jen.
of the World
Australian Institute of Marine Science, Australia. 3 volumes.
Eric H. 2001. Aquarium
Corals: Selection, Husbandry and Natural History
T.F. H Publications. 464 pp