latin little ring known worms worms large extant species including species exist adapted marine environments distinct tidal zones fresh water moist terrestrial environments symmetrical organisms textbooks use traditional division marine include like species research radically changed scheme viewing sub group sub group addition previously regarded separate regarded sub groups considered members super includes basic form consists multiple segments segment sets organs pair species use separate segments species poorly defined absent obvious signs species developed blood entirely blood vessels vessels segments near ends species built muscles act hearts species enable change shapes individual segments movement pass body improve effectiveness species incomplete blood main body cavity kind pump wide range techniques species turn inside drag sediment species reproduce use similar mechanisms severe injuries sexual reproduction normal method species reproduction studied minority living reproduction known produce larvae live sink miniature adults produce ring like bodies eggs ready emerge support terrestrial food chains prey regions important soil marine constitute species near shore environments encourages development ecosystems enabling water oxygen penetrate sea floor addition improving soil fertility serve humans food bait scientists observe monitor quality marine fresh water blood letting longer favor doctors species regarded endangered species harvested purpose centuries jaws studied engineers offer exceptional combination strength soft bodied fossils rare jaws tubes species late fossils represent oldest known fossil identified confidence comes million years ago early period fossils modern mobile groups appeared end million years ago disagree body fossils mid million years ago remains earliest fossils group appear period began million years ago classification diversity living species ranging size microscopic australian giant grow metres long research radically changed scientists views evolutionary family tree textbooks use traditional classification following sub groups species suggests multiple hairs segment function limbs organs thought marine animals species live fresh water fewer land species segment organs unique reproductive organ ring shaped pack saddle bodies produces stores eggs hatch eggs provide nutrition sub divided hairs includes sticky pad roof mouth feed wholly partly organic materials means shaped best known members marine species blood parasites mainly fish freshwater species predators ends bodies use like minute live spaces grains marine sediment treated separate class simple body structure regarded groups animals classified ways widely regarded discovered lack recognizable gut difficult classify classified separate recently classified family taxonomic history 19th century assigned members assigned regarded 1940s classified right molecular analysis concluded live mainly parasites past regarded close relatives suggested sub group analysis suggested closely related distinguishing features single feature distinguishes distinctive combination features bodies long segments divided externally shallow ring like called internally points species incomplete cases missing segments contain sets organs sharing common gut system nervous system makes inter dependent bodies covered cuticle outer covering contain cells cells skin underneath tough flexible hand rigid reach size closed systems blood makes entire circuit blood vessels description body consists segments practically identical having sets internal organs external greek meaning hair species sections regarded true segments contain standard sets organs develop way true segments section called greek meaning meaning mouth contains brain sense organs called greek meaning little tail contains generally underside section called greek meaning meaning mouth regarded true segment like segments segments develop time growth zone ahead youngest segment growth zone oldest pattern called growth groups including fixed maximum numbers segments add segments lives derived latin word meaning little ring body wall fibers usually layers spiral alternating directions fibers cross cell deep skin layer marine live tubes lack tubes similar structure protect skins tissue words combination cells non cellular materials layers muscles develop lining body cavity circular muscles segment longer contract longitudinal muscles usually distinct strips segment shorter oblique internal muscles connect underside body hairs project provide traction capabilities simplest form paired near segment limbs bear complex tips example like hooked moderately flexible formed hair forming cell muscles extend produce forming fine hair like extensions increase area available complete withdraw leaving parallel tunnels run length structurally different rigid single internal cavity mounted flexible joints shallow pits cuticle nearly function limbs major groups lack paired extensions body wall muscles derived circular muscles body supported internally large thick tube dwelling ridges tips bear hooked active swimmers divided large upper lower short trunk generally fringed fused gills nervous system senses brain generally forms ring round throat consisting pair local control centers linked nerve pair brains generally segment mobile active brain enlarged complex visible sections rest central nervous system generally ladder like consisting pair nerve run body segment paired linked transverse connection branching system local nerves runs body wall body main nerve fused tube dwelling genus single nerve chord located muscle fiber cell controlled speed power fiber depends combined effects different system controls group muscle fibers longitudinal nerve include giant output signal lines nerve cells large diameter decreases resistance allows transmit signals exceptionally fast enables worms withdraw rapidly danger shortening bodies experiments shown cutting giant prevents escape response affect normal movement sensors primarily single cells detect light chemicals pressure waves contact present head parts body neck organs paired structures found thought combinations little eyes detect direction light coming camera eyes compound eyes probably form images compound eyes probably evolved independently eyes tube worms use widely spread bodies detect shadows fish quickly withdraw tubes tube dwelling tilt balance sensors tell way genera heads feeding antennae structurally similar probably mainly system pair body segment separated segments vertical forms sandwich tissue middle membrane serves lining preceding following segments similar lining pair blood vessels main nerve embedded modified cells words bodies form bases extend form muscle fibers body wall form radial circular muscles circular muscles blood vessels gut parts especially outside gut form cells perform similar functions producing storing fat producing oxygen carrier breaking proteins turning waste products waves expansion sweep body body crawl swim animals enable circular longitudinal muscles change shape individual segments making segment separate fluid filled balloon incomplete semi movements example movements body small marine species means fine muscle powered hairs turn inside penetrate sea floor drag fluid contains cells defend animals parasites species contain respiratory pigment red species green dissolved provide oxygen transport segments respiratory pigment dissolved blood species developed generally blood vessels running long bodies gut upper carrying blood forwards lower carries backwards networks body wall gut transfer blood main blood vessels parts segment need oxygen nutrients major vessels especially upper pump blood contracting forward end upper blood vessel enlarged muscles form heart forward ends vessels connect upper lower main vessels function hearts species poorly developed generally blood vessels rely circulation delivering nutrients oxygen closest relatives body structure uniform group significantly different including members tissue layer body wall thick occupies body widely separated run length body function main blood vessels upper lower lined like unlike blood vessels generally use rear ends like upper surface including skin group belong gills associated segments extensions gills tube usually cluster end stronger water flow feeding feeding structures mouth region vary widely little animals muscular turned inside extend animals foremost segments lack muscles segments contract sharp increase fluid pressure segments quickly families evolved jaws seizing prey biting pieces vegetation dead decaying matter hand predatory jaws selective deposit generally live tubes sea floor use find food particles sediment mouths filter use crowns covered wash food particles mouths non selective deposit soil marine sediments mouths generally sticky pads roofs mouths pads capture prey muscular teeth gut generally straight tube supported vertical segments ends underside members tube dwelling family gut blocked swollen lining houses bacteria worms total weight bacteria convert matter hydrogen carbon dioxide organic matter feeds hosts worms extend gas flows absorb gases needed bacteria blood vessels use remove waste products use systems use stage process fluid waste products extracted filtered absorb usable materials dumping toxic spent materials difference combine stages organ perform second rely mechanisms special filter cells walls blood vessels let small molecules pass fluid points fluid enters forward second stage filter exit opening body wall following segment result segment growth zone structure extracts following segment filter discharge segment contains extraction structure passes second contain structures filter discharge reproduction life cycle reproduction reproduce dividing pieces new individual parent remains complete organism reproduce entirely reproduce summer sexually autumn reproduction dividing pieces seen use similar mechanisms suffering damage genera single segment heads removed complex animals severe damage hand sexual reproduction thought originally animals separate sexes released sperm water eggs develop larvae live later sink sea floor miniature adults head small area round tail piece narrow band immediately growth zone produces new segments rest segment contains mouth living marine animals unknown species known follow pattern use similar external produce yolk rich eggs reduce time needs spend eggs miniature adults emerge larvae rest care eggs hatch producing covered masses eggs tend eggs bodies species keeping eggs bodies hatch species use variety methods sperm transfer example females collect sperm released water males sperm female guarantee representative sample reproductive patterns simply reflects scientists current knowledge breed lives breed continuously breeding seasons remain sex lives significant percentage species change sex lives reproduction studied lack permanent uncertain produce sperm species rear body splits separate individual lives long swim suitable environment usually near surface spawn mature group includes species younger adults function males female maturity developed store partners sperm sperm stores produces collects sperm development eggs takes place eggs transferred produces yolk eggs nutrients developing hatch miniature adults larvae ecological significance book formation vegetable mould action worms presented scientific analysis contributions soil fertility live entirely surface generally moist leaf litter soil oxygen water penetrate surface worms help produce soil mixing organic mineral matter accelerating organic matter making quickly available organisms concentrating minerals converting forms plants use easily important prey birds ranging size mammals ranging cases essential endangered birds terrestrial invasive situations areas north_america example native thought killed glaciers worms currently found areas introduced areas primarily europe recently asia northern hardwood forests especially negatively impacted invasive worms loss leaf soil fertility changes soil chemistry loss ecological diversity especially concern state wisconsin listed prohibited species migrate limited distance annually spread invasive worms increased rapidly worms dirt vehicle tires marine account dwelling animal species coral reefs tidal zones species increase penetration water oxygen sea floor sediment encourages growth populations bacteria small animals alongside blood little direct harm victims transmit dangerous hosts small tube dwelling transmit parasites cause disease fish interaction humans significant contribution soil fertility rear end worm marine tunnels coral order spawn surface people regard spawning find worms effective bait artificial flies worms kept days tin lined damp moss commercially important bait food sources proposals farm order reduce fishing natural populations marine predation causes losses fishery operations scientists study aquatic monitor oxygen content pollution levels fresh marine water accounts use medically dubious blood letting come china india ancient rome later europe 19th century medical demand high areas stocks exhausted regions imposed restrictions exports treated endangered species iucn cites recently assist provided anti compounds important prevents spreading jaws strong lighter hard parts organisms calcium advantages attracted attention engineers investigations showed jaws unusual proteins strongly evolutionary history fossil record soft bodied fossils rare fossil record consists mainly jaws species tubes fossils ways resemble similarities vague fossils classified confidence small fossil million years ago classified authors sea belong earliest fossils widely accepted canada formed million years ago early found australia little older possibly lacks typical features features usually found associated simon conway morris reported million years old concluded oldest known date vigorous debate fossil early million years ago early jaws found crown group appeared date probably appeared somewhat later end million years ago fossils modern mobile groups appeared fossil tubes look like modern tubes clearly produced date million years ago earliest good evidence occurs period began million years ago suggested animals evolved time flowering plants early cretaceous million years ago trace fossil consisting convoluted partly filled small evidence present early period million years ago body fossils going mid million years ago tentatively classified uncertain disputed family tree traditionally divided major groups turn divided include best known members years clear arrangement approximately families higher level groups attempted step terms bringing acceptable level based structures divided species look like great majority divided distinguished having long use feeding live tubes active reinforced internal spines molecular compare similarities differences gene presented different view branch family tree decades regarded separate placed branches tree subsequent molecular analyses similar scale presented similar conclusions colleagues compared genes taxa words considered closely related included indication organisms study placed larger tree life cross check study analysis genes including original taxa analysis agreed branches family tree concluded classification useless members alleged groups scattered family tree derived comparing taxa addition placed generally regarded time separate branch tree concluded sub group sister group accepted analyses based molecular main conclusions scientific consensus details family tree remain uncertain addition writing classification previously independent molecular analyses undermine emphasis decades previous writings placed importance classification invertebrates analyses found parent group completely bodies rear parts bodies appear disappear easily course evolution previously thought study noted ladder like nervous system associated universal previously thought members major animals includes grouped super group animals obvious members genes drive appear close relatives easy assume evolved bodies independently assume ancestral disappeared descendant current view grouped fan like feeding structures larvae members basal distinctive relationships members known regarded members animals hypothesis supported fact group including follow similar pattern egg development cells divide cell stage descendants cells form spiral pattern embryo cells words roles descendants play adult animal predicted early stage development pattern described spiral
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