Editing Coral (section)

===Stony corals===
{{main|Scleractinia}}{{see also|Hexacorallia}} 
[[File:Montastrea cavernosa.jpg|thumb|''[[Montastraea cavernosa]]'' polyps with tentacles extended]]
The polyps of stony corals have six-fold symmetry. In stony corals, the tentacles are cylindrical and taper to a point, but in soft corals they are pinnate with side branches known as pinnules. In some tropical species, these are reduced to mere stubs and in some, they are fused to give a paddle-like appearance.<ref name=Sprung>{{cite book |title=Corals: A quick reference guide |last=Sprung |first=Julian |year=1999 |publisher=Ricordea Publishing |isbn=978-1-883693-09-1 |page=145 }}</ref>

Coral skeletons are biocomposites (mineral + organics) of calcium carbonate, in the form of calcite or aragonite. In scleractinian corals, "centers of calcification" and fibers are clearly distinct structures differing with respect to both morphology and chemical compositions of the crystalline units.<ref>{{Cite journal|last1=Cuif|first1=J.P.|last2=Dauphin|first2=Y.|date=1998|title=Microstructural and physico-chemical characterization of 'centers of calcification' in septa of some Recent scleractinian corals|journal=Paläontologische Zeitschrift|volume=72|issue=3–4|pages=257–269|doi=10.1007/bf02988357|bibcode=1998PalZ...72..257C |s2cid=129021387|issn=0031-0220}}</ref><ref>{{Cite journal|last1=Cuif|first1=J.P.|last2=Dauphin|first2=Y.|last3=Doucet|first3=J.|last4=Salomé|first4=M.|last5=Susini|first5=J.|date=2003|title=XANES mapping of organic sulfate in three scleractinian coral skeletons|journal=Geochimica et Cosmochimica Acta|volume=67|issue=1|pages=75–83|doi=10.1016/s0016-7037(02)01041-4|issn=0016-7037|bibcode=2003GeCoA..67...75C}}</ref> The organic matrices extracted from diverse species are acidic, and comprise proteins, sulphated sugars and lipids; they are species specific.<ref>{{Cite journal|last1=Dauphin|first1=Y.|last2=Cuif|first2=J.P.|last3=Williams|first3=C. T.|date=2008|title=Soluble organic matrices of aragonitic skeletons of Merulinidae (Cnidaria, Anthozoa)|journal=Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology|volume=150|issue=1|pages=10–22|doi=10.1016/j.cbpb.2008.01.002|pmid=18325807|issn=1096-4959}}</ref> The soluble organic matrices of the skeletons allow to differentiate [[zooxanthellae]] and non-zooxanthellae specimens.<ref>{{Cite journal|last1=Cuif|first1=J.P.|last2=Dauphin|first2=Y.|last3=Freiwald|first3=A.|last4=Gautret|first4=P.|last5=Zibrowius|first5=H.|date=1999|title=Biochemical markers of zooxanthellae symbiosis in soluble matrices of skeleton of 24 Scleractinia species|journal=Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology|volume=123|issue=3|pages=269–278|doi=10.1016/s1095-6433(99)00059-8|issn=1095-6433}}</ref>