singular greek carry commonly known animals live marine waters worldwide distinctive feature groups use swimming largest animals swim means adults species range millimeters size like bodies consist mass layer cells outside lining internal cavity layers cells deep cell deep authors combined groups rely water flow body cavity increasing awareness differences persuaded recent authors classify separate resemble having nerve net brain studies suggested differ ways animal evolved independently animals predators taking prey ranging microscopic larvae adults small crustaceans exceptions juveniles species live parasites adults species feed favorable circumstances eat times weight day species possibly fully described named textbook examples egg shaped bodies pair retractable fringed little covered sticky cells capture prey wide range body forms including flattened deep sea adults species lack coastal lack prey huge mouths armed groups large act teeth variations enable different species build huge populations area different types prey capture wide range methods spiders use species single animal produce eggs sperm meaning egg needing mate simultaneous produce eggs sperm time eggs sperm mature different times generally external eggs inside parents bodies kept hatch young generally species look like miniature gradually changing adult shapes grow exceptions young miniature large mouths young live like reach near adult size sink rapidly adult form species juveniles capable reproduction reaching adult size shape combination early reproduction enables small populations grow explosive rate abundant summer months coastal locations places uncommon difficult find bays occur high numbers predation control populations small organisms plants vital marine food chains accidentally introduced black_sea blamed causing fish stocks collapse eating fish larvae organisms fed fish situation aggravated factors fishing long term environmental changes promoted growth population later accidental introduction helped problem despite soft gelatinous bodies fossils thought represent apparently rows modern forms found far early million years ago position evolutionary family tree animals long debated majority view present based molecular closely related recent molecular analysis concluded common ancestor modern like modern groups appeared relatively recently probably cretaceous extinction event million years ago evidence accumulating 1980s indicates words include descendants single common ancestor traditional groups descendants distinguishing features form animal complex complex sea etc complex include animals unlike cells bound inter cell connections carpet like basement membranes muscles nervous systems sensory organs distinguished animals having sticky adhere prey species lack 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 regard ranging millimeter meters size largest non colonial animals use hairs main method species strips called rows run length bodies bear like bands called stacked rows beat touch means bearing greek stem form meaning greek meaning carrying description relatively species wide range body plans coastal species need tough withstand waves sediment particles oceanic species fragile difficult capture intact study addition oceanic species preserve known mainly photographs observers notes attention recently concentrated coastal genera textbooks base descriptions body species symmetrical main axis oral mouth opposite end canals near terminate anal pores mirror symmetry symmetry words animal half circle looks started common features body layers like sea etc bodies consist relatively thick like layers cells bound inter cell connections basement membrane layers cells cells upper layer cell outer layer outer skin consists sensory cells cells protects body cells transform types cell specialized parts body outer layer contains found surface capturing prey cells bearing multiple large inner layer contains nerve net cells act muscles internal cavity forms mouth usually closed muscles throat wider area center acts stomach system internal canals branch active parts animal mouth roots present underside row branches round sensory complex far end mouth branches terminate anal pores inner surface cavity lined mouth developed muscles parts canal system different sides nearest organ supplies nearer composed tall cells store nutrients internal compartments cells produce eggs sperm produce organ covered cells water canals punctuated pores surrounded double connect feeding prey muscular resulting canal system beating cells canals help transport nutrients muscles anal pores unwanted small particles unwanted matter mouth little known rid waste products produced cells help remove help adjust animal pumping water outer surface bears usually rows called swimming plates swimming rows oriented run near mouth oral pole opposite end pole spaced evenly body patterns vary species species rows extend distance pole mouth called plates run row consists thousands unusually long millimeters unlike conventional structure arranged pattern arranged pattern extra compact suspected supporting function normally beat propulsion stroke away mouth reverse direction usually swim direction mouth eating unlike trying escape predators species accelerate times normal speed species reverse direction escape behavior reversing power stroke plate uncertain control experiments shown species rely pressure adapt water different body normally concentrated enter dense water body cavity pump increase bulk decrease density avoid sinking conversely strength pump water reduce volume increase density nervous system senses brain central nervous system instead nerve net like forms ring round mouth near structures rows present sensory complex mouth largest single sensory feature organ opposite end mouth main component balance consisting tiny grain calcium supported called sense orientation protected transparent dome long automatically try resting equally instead response determined animal mood words overall state nervous system example trailing captures prey rows reverse spinning mouth prey bodies rounded nearly spherical times cylindrical egg shaped common coastal sea egg shaped body mouth narrow end individuals uniformly round opposite sides body extends pair long slender housed withdrawn species bodies flattened wider plane typically fringed little genera simple densely covered microscopic capture prey sticking specialized mushroom shaped cells outer layer main components head chambers contain stalk anchors cell lower layer spiral thread round stalk attached head root stalk function spiral thread uncertain absorb stress prey tries escape prevent torn apart addition members genus feed mainly incorporate victims eating similarly incorporate bodies defense differ significantly contain muscle cell type unknown relaxed known relaxed types movement capturing prey flick quickly lure prey like small worms round prey unique movement powered muscle motion produced smooth muscles highly specialized type prey accomplished largely return inactive state smooth muscle rows run near mouth opposite end spaced evenly round body beat rhythm like mexican wave groove runs dome splits connect adjacent rows species runs way rows forms mechanical system beat rhythm water disturbances created pair muscular extensions body project mouth originate corners mouth running convoluted grooves spreading inner surface trailing far mouth species gelatinous projections edged produce water currents help direct microscopic prey mouth combination structures enables feed continuously suspended prey rows originating pole usually extending body species extensions rows passive moving water rows propulsion long active movements contribute propulsion members genera escape danger jet expelled water drives backwards quickly unlike movements coordinated nerves water disturbances created row beat mexican wave style coordinated rows enabled grow larger shapes egg like unusual species described classified primitive body like floating disk like resting sea bed known feeding large inside large mouth filling body bears oral end fused thousand large able bite pieces prey large swallow field mouth lips species pair narrow strips cells stomach wall mouth shut animal feeding forming connections opposite strip tight closure animal pursuing prey body forms pair small oral pair body circular oval cross section extends inner surfaces discovered known species like bodies shortened oral direction short rows surface mouth originating near pole capture prey movements bell possibly short belt animals ribbon shaped animals mouth organ aligned middle opposite edges ribbon pair rows edge emerging groove oral edge stream wing like body surface swim bodies beating rows known species worldwide distribution warm warm temperate waters venus largest meters long slowly rapidly typically centimeters long faster described motion oval bodies flattened oral direction pair bearing surface surfaces muscular foot known species lack rows usually colored live rocks algae body surfaces invertebrates revealed long seen streaming current reproduction development adults species tissues damaged removed reproduce splitting edges flat bodies fragments develop new individuals species words function males females time species genus individuals remain single sex lives located parts internal canal network rows eggs sperm released pores external species use internal eggs brood chambers hatch self occasionally seen species genus thought species self fertile development eggs direct words distinctive form juveniles groups generally resemble miniature adults genus juveniles like adults lack species juveniles gradually develop body forms parents groups flat dwelling juveniles behave like true larvae live occupy different ecological niche parents attain adult form radical dropping sea floor species juvenile appear capable producing small quantities eggs sperm adult size adults produce eggs sperm long sufficient food run short food stop producing eggs sperm shrink size food supply improves grow normal size resume reproduction features capable increasing populations quickly colors live near surface transparent deeper living species strongly example species known red illustration formally described generally live attached sea organisms similar colors host organisms gut deep sea genus red hides rows produce rainbow effect caused scattering light species light usually blue green seen darkness significant groups including known genus incapable species including disturbed produce ink bodies juveniles brightly relation body size adults bodies detailed statistical investigation suggested function produced exact color aspect animals environments depth live coastal mid ocean waters caused activation calcium activated proteins named cells called confined canals rows genes genes expressed genes developing raising possibility light production light detection working animals ecology distribution found marine environments polar waters tropics near coasts mid ocean surface waters ocean depths best understood genera coastal forms likely collected near shore found fresh water prey predators predators genus partly parasitic food plentiful eat times weight day mainly surface water species prey animals ranging size microscopic including fish larvae small adult crustaceans members genus prey incorporate prey cells instead compared spiders wide range techniques capturing prey hang water ambush predators like jumping spiders sticky end fine thread spiders variety explains wide range body forms species feeds exclusively close relatives sea form large chain like floating colonies juveniles attach like parasites large swallow members genus reach high population place time different types prey long mainly capture relatively strong swimmers adult generally feeds smaller weaker swimmers larvae regarded dead ends marine food chains thought low ratio organic matter salt water poor diet animals difficult identify remains possible predators remain intact long provide clue detailed investigation salmon showed fish digest times fast equal weight provide good diet prey mainly turtles eat large quantities temporarily populations large seasonal variations population fish prey greater effect populations specialist observation fishes deliberately feeding gelatinous red_sea larvae sea parasites larvae fish reach adulthood ecological impacts balance marine ecosystems preventing abundance eating plants dominant marine producers organic matter non organic ingredients hand late 1980s accidentally introduced black_sea sea ballast tanks ships blamed causing sharp drops fish catches eating fish larvae small crustaceans feed adult fish equipped invade new territories predicted successfully black_sea breed rapidly tolerate wide range water temperatures impact increased chronic gave entire ecosystem short term boost causing population increase faster normal absence efficient predators introduced populations areas eventually brought control accidental introduction eating north american cooling local climate significantly slowed animal abundance area unlikely restored pre levels late 1990s appeared arrived shortly expected reduce eliminate impact reached eastern mediterranean late 1990s appears thriving north_sea baltic_sea classification number known living species uncertain named formally described turned identical species known scientific names estimates valid species deep sea forms recognized distinct analyzed detail support formal description naming traditional classification divides classes contains order family genera species species divided following orders egg shaped animals long paired thick flattened animals live near sea bed lack adults use attach surfaces pair small round mouth extended like short like umbrella ribbon shaped largest evolutionary history fossil record soft gelatinous bodies extremely rare fossils fossils interpreted found places environment exceptionally suited preservation soft tissue mid-1990s specimens good analysis known members crown group early period additional species found canadian rocks similar age million years ago mid period apparently lacked rows far typical living species appear internal organ like structures unlike found living fossil species reported large mouth apparently surrounded folded edge muscular evidence china year later suggests widespread different modern species example fossil rows mounted prominent represent early like fossil china dated million years ago similar preceding period simon conway morris found branches considered rows filter feeding suggested evolutionary aunt originated animals descendants swimmers changed feeding mechanism propulsion system million years old fossils china wholly extinct class named complex internal skeleton long spines relationship animal relationship rest important understanding early evolution animals origin focus debate years purported sister lineage sister sister sister animal series studies looked presence absence members gene families signalling pathways nuclear signaling channels showed evidence scenarios sister sister animal recent studies comparing complete animal supported sister lineage animals position suggest muscle cell types lost major animal evolved independently lineage researchers argued placement sister animals statistical caused high rate evolution earliest animal instead known animal lack true genes relationships modern like larvae widely assumed common ancestor resembled having egg shaped body pair retractable purely morphological analysis concluded words contain descendants single common ancestor instead found families similar members orders suggested common ancestor modern like like molecular phylogeny analysis species including recently discovered ones confirmed concluded common ancestor modern like found genetic differences species small small relationships remained uncertain suggests common ancestor modern relatively recent lucky survive cretaceous extinction event million years ago perished analysis include representatives concluded probably closely related group diagnosis uncertain
Ctenophora