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localisation biotique

(from 'Les coraux' - B.Robin, C.Petron, C.Rives - Les Editions du Pacifique)

Outer slope

Seaward part of the reef, always below water, slope of variable steepness. Two zones are separated (each divided into 2 subzones) essentially by their depth (considered in terms of variations of light intensity and agitation) and by the initial topography.

Reef flat

The reef flat corresponds to subhorizontal upper part of the reef construction. It may be emersed during low spring tides. It includes a variety of communities which are distributed in one of the two majors divisions:

Back reef

The back reef is divided in two zones :


Structure of a coral

(from 'Coral Reef Handbook' - P.Mather, I.Bennet - Surrey Beatty &sons Pty Lted)

A - Polyp
B - Cross section of a polyp and of the skeleton
C - Soft parts have been removed to show the skeleton only (corallite)


Collection of individuals (polyps) and their skeletal production (corallites). Some species however are solitary (do not form colonies).


Cup-shaped skeletal unit, secreted by the polyp and in which it can withdraw and shelter. Each corallite is composed of two parts: the basal plate and the wall (or theca).

Basal plate

Horizontal skeletal element (calcareous lamella) which forms the base of the corallite on which the wall (or theca) is established.

Wall (Theca)

Calcareous element which constitutes the boundary of the corallite and separates it from the outside. Its development may vary significantly. It may be symetrical or not, in which case it forms a hood.

Septa (Sclerosepta)


Axial element arising from the basal plate in the center of the corallite, with variable shape (styliform, lamellar, papillose) and ornamentation.

Coenosteum (Peritheca)

Collection of skeletal elements located between the corallites. It is divided into 2 parts :


Furrow of variable depth separating two or several corallites.

Structure d'un corail

1 - tentacles
2 - mouth (stomodeum)
3 - mesentery
4 - gastric cavity
5 - basal plate
6 - polyp
7 - corallite
8 - coenosteum
9 - dissepiment
10 - columella
11 - septum
12 - wall (theca)

(from 'Ihre Verbreitung, Tierwelt, und ökologie' - Schuhmacher, Helmut - BLV Verlagsgesellschaft mbH, München, 1976)

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© IREMIA - IKBS team - 11/2000