Corals have adapted to different environments through time by evolving unique morphological or physiological features. There are hundreds of coral species, many with different colors, growth forms, and colony sizes. With so many coral species, scientists have developed a classification system to distinguish among different species based often on a such characters as a coral’s morphology and/or individual corallite (skeleton) shape and size (e.g., see http://nmita.geology.uiowa.edu/florlist.htm).
Corallite shape and size
There is a wide range of variation both in corallite shape and size. Many corals have round corallites, such as mountainous star coral, while other corals have more elliptical shaped corallites like the elliptical star coral (far left photo). The size of corallites also varies with species; some corals have small corallites like the lettuce coral (middle photo), while others have very large corallites (far right photo). The internal diameter of a corallite is measured across the corallite center between the inner wall margins and is classified as small (<1.5 mm), medium (1.5-10 mm), large (10-20 mm), or huge (>20 mm).
In addition to using corallite structure to identify coral species, the
morphology of the entire colony is also often used to distinguish one coral
from another. Similar to other animals, corals have a variety of growth forms –
some tall and thin, some short and robust. Generally, most corals can be
categorized in one of six general groups: branching,
mound, brain, plate, fleshy and flower. Often a single species can have
a variety of growth forms, especially at different depths; for example Diploria strigosa can form large round
heads, small hemispherical mounds, or massive columnar plates. Branching or
pillar corals have colonies composed of branches or elongated projections.
Mound corals include mounding hemispherical, irregular-shaped or encrusting colonies whose lower surface is usually attached to the substratum. Examples include mountainous star coral (Montastraea faveolata), massive starlet coral (Siderastrea siderea), elliptical coral (Dichocoenia stokesii), and mustard hill coral (Porites astreoides). Large mound corals often have slower growth rates than branching corals. Brain corals often form hemispherical mounds, but are characterized by their unique distribution of polyps that grow in a winding pattern to give a brain-like appearance. Examples include grooved brain (Diploria labyrinthiformis), knobby brain (Diploria clivosa), and maze (Meandrina meandrites).
Plate corals include plate, leaf, and sheet coral and grow in a flattened plate, saucer-like, or thin sheet fashion. They usually have thin disc-shaped colonies with corallites growing only on one side. Examples include lettuce coral (Agaricia agaricites) and thin leaf lettuce coral (Agaricia tenuifolia). Fleshy corals include plate and mound varieties but are distinguished by their large “fleshy” looking polyps. Examples include a variety of solitary disk corals and the spiny flower coral (Mussa spp.). Flower corals have solitary, encrusting or clumping growth forms and often have polyps on elongated stalks. Examples include smooth flower coral (Eusmilia fastigiata) and a variety of cup corals.
© 2000-2006 - AGRRA