containing species animals found exclusively aquatic freshwater marine environments predominantly marine species distinguishing feature specialized cells use mainly capturing prey bodies consist non living like substance layers cell thick basic body forms swimming symmetrical mouths surrounded bear forms single body cavity species produce colonies single organisms composed like like activities coordinated nerve net simple free swimming species possess balance sensing simple eyes reproduce sexually species having complex life cycles stages sexual stage grouped increasing awareness differences caused placed separate classified main groups wholly sea sea swimming box diverse group includes freshwater marine forms members colonial swimmers portuguese man war recently recognised class right sub group debate closer complex animals prey organisms ranging size animals times larger obtain nutrition algae parasites preyed animals including sea fish turtles form structural foundation coral reefs possess filled algae reef forming entirely restricted warm shallow marine waters found great depths polar regions freshwater fossil found rocks formed million years ago fossils present shortly million years ago million years later fossils build structures rare scientists currently think closely related evolutionary sisters closely related distinguishing features form animal complex complex complex include animals complex cells bound inter cell connections carpet like basement membranes muscles nervous systems sensory organs distinguished animals having fire like mainly capture prey species anchors like main layers cells sandwich middle layer like material called complex animals main cell layers intermediate like layer traditionally labelled type muscle complex animals arises middle cell layer result recent text books classify suggested evolved ancestors description basic body forms adult appear swimming species known alternate forms symmetrical like wheel tube respectively animals heads ends described oral nearest mouth mouth fringes equipped edges generally inner ring mouth consist colonies serve different purposes defense reproduction catching prey usually thin soft usually thick returns original shape muscles edge contracted squeeze water enabling swim sort jet propulsion skeletons supporting structure sea close mouths feeding water digestive cavity acts skeleton like water filled balloon use columns water filled cells support sea calcium tough proteins like colonial gives support protection connecting sections lower parts individual massive calcium collect materials sand grains shell fragments attach colonial sea sediment particles main cell layers animals words main cell layers complex animals having main layers main cell layers form cell thick attached basement membrane like separates layers layer faces known outside skin generally contains following types cells cells bodies form bases extend form muscle fibers parallel rows fibers outward facing cell layer generally run right angles fibers inward facing etc contains muscle cells like cells appear muscle cells nerve cells sensory cells appear muscle cells communicate gaps chemical signals flow motor nerve cells lie bases muscle cells cells replace lost damaged cells transforming appropriate types found bases muscle cells addition nerve cells inward facing stomach skin contains cells digestive species contains low concentrations subdue prey struggling contains small numbers like cells muscle cells species number middle layer cells types lower refers occurrence structurally different types individuals organism characteristic feature particularly forms colonial organisms like colonial individuals arising individuals separate tasks example feeding individuals individuals capable reproduction free living sexually individuals cells function remain connected bodies cells threads types known venom prey usually embedded victims species penetrate victim venom means small sticky hairs thread prey capture instead threads discharged building protective tubes owners live found order tube main components fine hair projects surface acts trigger tough capsule houses thread mixture chemicals include venom derived greek word means tube like extension wall points like finger rubber glove pushed fires finger pops cell finger tip reveals set anchor prey thread extension finger round fires thread usually hollow delivers chemicals target lid end lid single flaps arranged like pie cell body produces parts difficult study firing mechanisms structures small complex proposed rapid fibers round increase internal pressure thread like spring extends rapidly released case sea wasp chemical changes contents cause expand rapidly chemical changes liquid concentrated solution pressure forces water rapidly mechanism observed class producing pressures high similar air tanks fully extending thread little second fire lost capturing shrimp replaced takes hours firing types generally required trigger nearby sensory cells detect chemicals water respond contact combination prevents firing distant non living objects groups usually connected nerves fires rest group requires weaker minimum cells fire swim form jet propulsion muscles especially inside rim bell squeeze water cavity inside bell powers recovery stroke tissue layers thin provide little power swim currents control movement currents sea slowly rocks sea stream beds means like crawling like swim bases nervous system senses brains central nervous systems instead nerve nets consisting sensory generate signals response types motor tell muscles contract intermediate connect forming signal cables intermediate form act local coordination centers detect physical contact nerves inform prey attackers detected neighbouring fire communications nerve cells chemical small gaps chemicals flow process slow ensure muscles round rim bell contract simultaneously swimming control communicate faster electrical signals gap junctions complex swimming colonies sense tilt acceleration means chambers lined hairs detect movements internal mineral grains called body wrong direction animal rights increasing strength swimming movements low species simple eyes detect sources light box unique possess kinds true eyes lenses eyes probably form images clearly distinguish direction light coming negotiate solid colored objects feeding feed ways predation absorbing dissolved organic chemicals food particles water obtaining nutrients algae cells obtain majority food predation including depend completely absorbing dissolved nutrients algae carbon dioxide nutrients place sun protection predators predatory species use poison prey start digestive smell wounded prey makes fold prey mouth round edge bell short prey capture oral arms extensions edge mouth branched increase surface area trap prey suspended food particles swimming upwards spreading oral arms sinking species suspended food particles important oral arms rows beating creates currents flow mouth produce nets trap particles food digestive cavity cells release reduce prey usually hours digestive cavity colonial connecting tunnels cells absorb nutrients absorption hours cells days circulation nutrients driven water currents produced muscular movements nutrients reach parts digestive cavity nutrients reach outer cell layer animals thick transported mobile cells remains prey expelled mouth main waste product cells internal processes removed external internal water currents respiratory organs cell layers absorb oxygen expel carbon dioxide surrounding water water digestive cavity replaced nutrients absorbed expelled grooves allowing pump water digestive cavity opening mouth improves feeding allows animals use cavity skeleton control water pressure cavity food carry opposite problem excess oxygen prove toxic animals produce large quantities excess oxygen regeneration allowing recover injury reproduce limited ability small pieces collections separated cells enables recover apparently destroyed predators reproduction sexual sexual reproduction involves complex life cycle stages example box finds good site grows normally splits horizontally series juvenile process called juveniles swim slowly grow maturity grows continue periodically adults release sperm water breeding season phenomenon succession differently organized generations sexually free swimming called sexual phases confused generations found plants characterized spore producing form producing form shortened forms life cycle common example oceanic stage completely produce variety life cycles stages species remain attached responsible sexual reproduction extreme cases reproductive look like life cycle reversal formed directly involvement sexual reproduction process observed stage responsible sexual reproduction spawning generally driven environmental factors changes water temperature release triggered lighting conditions sunrise sunset phase moon species spawn simultaneously location sperm predators eat tiny percentage famous example great barrier reef non invertebrates produce turn water cloudy mass produce hybrids settle form known long survive species release chemicals attract sperm species eggs develop larvae dividing cells form hollow sphere depression forms end eventually digestive cavity depression forms end yolk animal pole forms end pole larvae called swim crawl means cigar shaped slightly broader end pole end eventually substrate species stage larvae large capable feeding algae help feed parents feeding capabilities extend larvae range avoid sites larvae little yolk lack algae settle quickly instead species rely extend ranges known reproduce means addition fragmented divide middle split middle addition methods split horizontally base reproduction makes daughter clone adult classification long time grouped increasing awareness differences caused placed separate modern generally classified main classes sea sea swimming box diverse group includes freshwater marine forms members colonial swimmers portuguese man war recently recognised class right sub group debate parasitic closely related small stage traditionally classified members recent research suggests regarded separate class microscopic parasites classified recently heavily modified closely related recent research suggests parasite egg cells closely related intermediate animals researchers classify extinct propose form completely separate ecology limited shallow waters depend algae nutrients life cycles stages limited locations offer stable major groups contain species escaped limitations worldwide range live freshwater appears coastal waters oceans form large near surface mid ocean sea sea fans live deep cold waters sea inhabit polar live near sea level reef building limited tropical seas maximum depth temperatures high low carbon dioxide levels usually classified animals live cool arctic waters range size long lion exceed diameter length prey ranges animals times larger parasites mainly major fish obtain algae dissolved nutrients predators include sea incorporate bodies self defense notably crown butterfly fish fish eat marine turtles eat sea relationship fish example clown fish live sea partner protects predators coral reefs form world productive ecosystems common coral reef include hard fire lace algae species effective primary producers words chemicals organic ones organisms use coral hosts use organic chemicals efficiently addition reefs provide complex varied habitats support wide range organisms reefs low tide level mutually beneficial relationship forests high tide level sea grass meadows reefs protect strong currents waves damage sediments rooted protect coral large fresh water additional level variety environment beneficial types coral reef animals example feed sea grass use reefs protection breeding evolutionary history fossil record earliest widely accepted animal fossils modern looking possibly million years ago fossils dated approximately identification embryos animals contested fossils rocks strongly resemble tubes structures presence implies diverged fossil classified sea pen recent study growth patterns modern cast doubt hypothesis leaving canadian body fossil fossils skeletons known recent rocks preserved soft bodied animals fossils resemble found rocks period early wiped extinction million years ago dominate reef construction algae played major era main reef builders wiped cretaceous extinction event million years ago main reef builders family tree difficult reconstruct early stages evolutionary family tree animals morphology shapes structures large differences plus complex animals comparisons difficult rely largely entirely molecular groups organisms according similarities differences usually dna generally thought calcium closely related complex animals groups proposed closely related formed group called hollow rely flow water single cavity feeding proposed closely related shared features lack example muscles middle layer recent analyses indicate similarities vague current view based molecular closely related grouping labelled suggests earliest similar larvae sea regarded sister group rest suggests earliest stage unclear groups acquired stage form splitting tip traditional grouping included morphology molecular indicate closely related box similarities double body walls extinct suggest closely related position nearest beginning family tree implies closely related supported fact share genes determine main axes body suggested simplified descendants animals stage muscle arises commit evolved early ancestors molecular analyses onwards important groups developmental genes variety fact especially sea retain genes present bacteria plants fungi mitochondrial unlike animals linear fragmented genes reason difference unknown interaction humans killed people 20th century particularly dangerous hand large considered east southeast_asia coral reefs long economically important providers fishing grounds shore buildings currents tides recently centers tourism vulnerable fishing mining construction materials pollution damage caused tourism beaches protected tides storms coral reefs best places housing tropical countries reefs important food source low technology fishing reefs adjacent seas despite great productivity reefs vulnerable fishing organic carbon produce carbon dioxide organisms middle levels food chain reaches larger species interest fishermen tourism centered reefs provides income tropical islands attracting photographers divers sports fishermen human activities damage reefs ways mining construction materials pollution including large fresh water storm drains commercial fishing including use dynamite fish capture young fish tourist damage caused boat anchors cumulative effect walking reefs coral mainly pacific_ocean long jewellery demand rose sharply 1980s large species order commonly consumed japan korea southeast_asia parts range fishing industry restricted daylight hours calm conditions short seasons march august november commercial value food products depends skill prepared masters guard trade secrets carefully low cheap preparation introduce undesirable amounts heavy metals sea wasp described world held responsible deaths difficult identify animal transparent cause mild symptoms seven box cause set symptoms called syndrome takes minutes develop hours weeks disappear hospital treatment usually required deaths books london isbn der der fischer isbn barnes invertebrates synthesis oxford 3rd edition chapter isbn invertebrates mass 2nd edition chapter isbn food ancient world moore introduction invertebrates cambridge chapter isbn und fischer isbn der berlin 5th edition isbn journal articles bridge mitochondrial dna structure molecular phylogeny recent classes proceedings bridge class level relationships molecular morphological evidence molecular biology evolution oxford reproduction online new biology online phylogenetic analysis und hamburg berlin developmental physiology online parasites review higher level recent morphological molecular phylogenetic analyses archived original retrieved
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