called hard marine animals live build hard skeleton individual animals known cylindrical body crowned oral disc mouth fringe species solitary colonial founding starts calcium protect soft body solitary colonial species usually millimetres diameter reproduce remain attached forming multi colony common skeleton metres diameter height according species shape appearance coral colony depends species location depth water movement factors shallow water contain organisms known tissues colour coral vary depending species contains closely related sea like armed cells known reproduce sexually species release sea takes place larvae drift species brood eggs reproduction colony detached occur world oceans colonial form reef structures found shallow waters sunlight solitary colonial form reefs occur depths light reaches appeared relationship currently unresolved framework modern coral reefs formed numbers expected decline effects global warming ocean anatomy solitary colonial colonies reach considerable size consisting large number individual soft parts members class like members group stage life cycle individual animals known cylindrical body crowned oral disc surrounded ring base material coral skeleton formed body wall consists layers mouth centre oral disc leads tubular descends distance body opening cavity fills interior body unlike cavity subdivided number thin sheets living tissue known located cavity walls retractable cup sits pulled sheet like muscles connected horizontal sheets tissue known extending outer surface skeleton completely covering sheets continuous body wall include extensions cavity food water different members colony colonial species repeated division causes forming colonies cases exist adjacent colonies species form single colony colonial species small ranging diameter solitary species large skeleton skeleton individual known lower body initially forms cup surrounding interior cup contains aligned plates projecting upwards base plates flanked pair added order result different ages adjacent symmetry skeleton radial pattern termed contrast fossil adjacent lie order increasing age pattern termed serial produces symmetry inserted modern skeletons composed calcium form crystals prehistoric non skeletal structure composed structure simple compound light solid case prehistoric order distinguished pattern growth colonial growth results new types new develops oral disc inside ring form individual separate row partially separated sharing oral disc series mouths grow margin elongated oral disc individual mouths surrounded single wall case brain results separate wall case lateral form basis trunk branches rate coral colony lays calcium depends species branching species increase height length year rate human hair grows like dome plate species grow year rate deposition varies examination cross sections coral bands deposition indicating annual growth like tree rings estimate age coral solitary gradually increase size deposit calcium produce new large example normally single mouth long thousand distribution occur world oceans main ecological groups colonial tend live clear shallow tropical waters world primary reef builders colonial solitary found regions ocean build reefs live tropical waters inhabit temperate seas polar waters live great depths zone ecology fall main categories reef forming contain non reef forming contain reef forming cells usually known million cells square coral tissue benefit organic compounds produce food oxygen additional energy derived produced enable grow rate times faster similar species typically grow shallow lit warm water moderate abundant oxygen prefer firm non muddy surfaces settle extend feed larger larger prey including invertebrates small fish addition capturing prey way produce films bodies trap small organic particles pulled mouth primary method feeding reduced absent example caribbean generally nocturnal skeletons day exposure light species feed day night non usually reef found beneath water thrive colder temperatures live total darkness energy capture suspended organic particles growth rates species non significantly slower counterparts typical structure susceptible mechanical damage life cycle great range reproductive strategies reproduce sexually species separate sexes colony male female individual having male female species brood eggs species sexual reproduction results production free swimming eventually undergo colonial species initial repeatedly divides rise entire colony reproduction common means reproduction colonial pieces branching detached storms strong water movement mechanical means fragments fall sea bed suitable conditions capable substrate starting new colonies massive shown capable forming new colonies process reef hobby increase stock necessity harvest wild adverse conditions certain species coral resort type reproduction form bail allow survive parent colony dies involves growth seal detachment settlement initiate new colonies species small balls tissue differentiate start calcium form new colonies eggs develop viable larvae sexual reproduction overwhelming majority taxa adult colonies temperate regions usual pattern synchronized release eggs sperm water brief spawning events related phases moon tropical regions reproduction occur year cases genus eggs sperm released rise surface increases concentration sperm eggs likelihood reduces risk self immediately spawning eggs delayed capability release polar bodies delay possibly degree self likely increases chance cross study species found cross actually dominant mating pattern species capable self varying evolutionary history little evidence base hypothesis origin plenty known modern species little fossil specimens appeared record million years ago million years later important reef builders success result teaming algae sub orders existence end appeared million years ago appearing middle cretaceous million years ago developed common ancestor like coral skeleton coral coral unlikely common ancestor skeletons arranged similarities common non ancestor early alternatively developed like ancestor associated development reef formation occurred occasion dna appears indicate group earliest reef builders small solitary individuals probably greatest diversity disappeared mass extinction event end cretaceous genera surviving recently discovered skeletons features characterize strengthened hypothesis independent origin early open question phenomenon evolved independently numerous occasions genera different families non members classification taxonomy particularly challenging species described advent diving little authors coral species varying different habitats collectors limited observing reef flats unable observe changes morphology occurred deeper water conditions nominal species described era rules nomenclature given described species precedence rest description poor environment country type specimen unknown concept species suspect regard large geographical ranges number sub populations geographic boundaries merge species morphological boundaries merge species definite species subspecies evolutionary relationships examined 19th early 20th centuries advanced 19th century classifications complex skeletal characters classification french based skeletal characters scheme developed observations skeletal particular attention structure pattern american wells patterns divide group addition considered features growth distinguished families wall type type classification french zoologist built earlier systems included observations involve characters recognized stressed importance observations proposing begin skeletal growth centers genetically derived diverse patterns centers vital classification later showed established morphological classifications examples evolution fossils recent taxa rise molecular techniques end 20th century prompted new evolutionary different ones founded skeletal data results molecular studies explained variety aspects evolutionary biology including connections extant taxa supplied support extant founded fossil record analysis mitochondrial undertaken american found molecular data supported assembling species existing families traditional example genera affiliated different located branch phylogenetic tree addition distinguishing morphological character separates molecular differences australian zoologist workers analyzed obtain similar results concluding traditional families plausible incorrect established including descendants common ancestor divided groups robust complex suggested morphological molecular systems future classification schemes families lists following families included order
Scleractinia