Scleractinian Coral Family, Astrocoeniidae

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Family Astrocoeniidae: (Gk. aster, star; Gk. koinos, shared).... most likely relating to the shared walls of each calice. All four genera feature style-like columellae and neatly arranged solid septa in 2-3 distinct cycles.
The systematic position of this small family has been repeatedly changed. Its current position in the coral family tree, is only weakly supported by the fossil record and awaits further study by molecular techniques. Affinities with the Pocilloporidae seem clear on the basis of morphology of extant genera. This small family is represented by just four endozumbiotic (zooxanthellate) genera (Stylocoeniella, Stephanocoenia, Paluastrea, and Madracis) containing 13 species, ten of which are found in waters around PNG, while Madracis senaria, M.mirabilis, and M.formosa are entirely Atlantic species. In PNG, they can be especially abundant on steep drop-offs that are influenced by strong upwelling. In these areas they tend to form larger colonies - compared to back-reef turbid habitats, where they form small encrusting colonies rarely more than a few centimeters in diameter (for morphological characteristics see table).	Astrocoeniidae (130kB)
Generally, all members of this family form large encrusting colonies up to 50cm in diameter can be observed on steep drop-offs, are abundant in crevices and under overhangs, and can be found even at depths of 30m. Interestingly, colonies up to 2m in diameter were found at the southern limits of coral reef distributions along the east and west coast of Australia. Thus, temperature may be a significant factor determining colony size in this family - it remains to be seen if global climate change affects this family.
Key to the family Astrocoeniidae Colonies encrusting, corallites inconspicuous Coenosteum style present: Genus *Stylocoeniella* No coenosteum style: Genus *Stephanocoenia* Colonies becoming branching, corallites conspicuous Septa with free margins: Genus *Palauastrea* Septa fused with columella: Genus *Madracis*
Indo-Pacific genera: ---------------------------------------------------------------------------------------------------------- Stylocoeniella (Gk. stylos, pillar; koinos, shared; L. -ellus, diminuitive suffix): Forms brown-red, or greenish encrusting colonies that are no more than few cm in diameter; they are found in crevices or on the dead lower parts of other coral colonies and develop small knobby and columnar colonies. Corallites are round to square in outline and separated by coenosteum. The upper outer edge of one of the primary septa of each corallite is raised and merges with the coenosteum to form a styliform pillar (calicular, or pillar-like structure). Septa are barely visible. There are 12 septa arranged in 2 alternating cycles of 6; with the primary cycle radiating from the columella. Dispersal capability of all species is, presumably, good. PRESENT DISTRIBUTION: Red Sea to central Pacific. GENERAL ABUNDANCE: uncommon, cryptic. FOSSIL RECORD: Eocene of the Indo-Pacific, Oligocene of the Caribbean and Tethys. NUMBER OF EXTANT SPECIES: 3 known species - all occur on small, remote Cocos (Keeling) Atoll. Palauastrea (Island of Palau, location first found; Gk. aster, star): Forms branching colonies that may be up to 30cm tall. Superficially they closely resemble Porites. The branches taper gradually and usually have a rounded or slightly knobby extremity (blunt ends). Sometimes the branches fuse together. The corals are light brown, pinkish, with a yellow oral disk. There are 12 yellow to pinkish-brown tentacles. Corallites have similarities with those of Stylophora. Calices are about 0.6-0.8mm in diameter and are immersed. There are two alternating septal cycles, with the 6 broad septa of the 1st cycle reaching the columella. Coenosteum is smooth. Perithecal areas are covered with small spines. This rare genus is usually found of sand in turbid conditions. PRESENT DISTRIBUTION: central Indo-Pacific. Central Indo-Pacific. GENERAL ABUNDANCE: uncommon. FOSSIL RECORD: none. NUMBER OF EXTANT SPECIES: 1 known species. This species is frequently confused in situ with Porites cylindrica. Atlantic genus: ---------------------------------------------------------------------------------------------------------------- Stephanocoenia (Gk. stephos, crown; koinos, shared): S.michelinii forms encrusting or massive colonies, brownish in color. A total of 24 septa are arranged in 3 cycles, but only the septa of the 1st two cycles reach the massive columella. These septa ere exsert and have well-developed paliform lobes. PRESENT DISTRIBUTION: western Atlantic. GENERAL ABUNDANCE: Sometimes common. FOSSIL RECORD: Cretaceous (?), Eocene of the Caribbean, Oligocene of the Caribbean and Tethys. NUMBER OF EXTANT SPECIES: 1 known species. Circum-tropical genus - although dominating within the Atlantic region:---------------------------------------- Madracis (L. madre, mother; Gk. akis, point): This genus is the only survivor of the Pocilloporidae in the Atlantic. It has both endosumbiontic (zooxanthellate) and azooxanthellate species in both the Atlantic and Indo-Pacific. Although these species are readily identifiable, they do not form sub-generic groups, and are not separable in the fossil record. This cryptic genus forms encrusting, nodular, or branched colonies that are easily confused with Stylocoeniella; the branches seldom exceed 1.5cm in diameter. Corallum in cream, yellow, brown, green, or reddish in color. Calices are small, superficial, or maybe well spaced, or crowded. They are about 1-2mm in diameter and display 10 well developed septa (rarely 8), all of which reach the columella. Paliform lobes are absent. The columella is solid and styliform. PRESENT DISTRIBUTION: western Indian Ocean to eastern Pacific and western to eastern Atlantic. GENERAL ABUNDANCE: uncommon, mostly cryptic in the Indo-Pacific, much more common in the western Atlantic. FOSSIL RECORD: Cretaceous, Eocene of the Caribbean, Miocene of the Tethys. NUMBER OF EXTANT (endosymbiotic) SPECIES: 9 known species.