the asterozoa are a subphylum in the phylum echinodermata .

characteristics include a star-shaped body and radially divergent axes of symmetry .

the subphylum includes the two classes asteroidea , the starfish , and ophiuroidea , the brittle stars and basket stars , and the extinct order somasteroidea .

asterozoa

asterozoa .
a dictionary of zoology . . retrieved july 09 , 2018 from urltoken urltoken
asterozoa .
a dictionary of earth sciences . . retrieved july 09 , 2018 from urltoken urltoken
asterozoa .
a dictionary of zoology . . encyclopedia . com . ( july 9 , 2018 ) . urltoken
asterozoa .
a dictionary of earth sciences . . encyclopedia . com . ( july 9 , 2018 ) . urltoken
what made you want to look up asterozoa ? please tell us where you read or heard it ( including the quote , if possible ) .
taxonomy in the current linnean system ophiuroidea is regarded as a class . following a more phylogenetic view its parent would be asterozoa according to a popular hypothesis . however , according to another equally parsimonious view , ophiuroidea and asteroidea are not sister taxa , which invalidates asterozoa as their parent . [ details ]
mcknight , d . g . 1975 . classification of somasteroids and asteroids ( asterozoa : echinodermata ) . journal of the royal society of new zealand . 5 : 13 - 19 .
mcknight , d . g . 1975 . classification of somasteroids and asteroids ( asterozoa : echinodermata ) . j . roy . soc . n . z . 5 : 13 - 19 .
reich a , dunn c , akasaka k , wessel g . data from : phylogenomic analyses of echinodermata support the sister groups of asterozoa and echinozoa . database : dryad data repository [ internet ] .
citation : reich a , dunn c , akasaka k , wessel g ( 2015 ) phylogenomic analyses of echinodermata support the sister groups of asterozoa and echinozoa . plos one 10 ( 3 ) : e0119627 . urltoken
telford mj , lowe cj , cameron cb , ortega - martinez o , aronowicz j , oliveri p , et al . phylogenomic analysis of echinoderm class relationships supports asterozoa . proc biol sci . 2014 ; 281 .
the class of sea stars form the subphylum asterozoa , together with the brittle stars ( ophiuroidea ) . the seven orders of sea stars include more than 2000 species worldwide , 43 of them are registered in norway .
asterozoa in which the alimentary organs are essentially confined to a central disc from which the arms are distinctly demarcated and capable of performing the locomotor movements , the tube - feet serving as non - suctorial , sensory tentacles .
blake , daniel b . guensburg , thomas e . and lefebvre , bertrand 2016 . new early paleozoic asterozoa ( echinodermata ) from the armorican massif , france , and the western united states . annales de paléontologie , vol . 102 , issue . 3 , p . 161 .
, is basal within the subphylum asterozoa . members are most readily recognized by presence of series of rod - like so - called virgal ossicles extending laterally from each ambulacral ossicle . five somasteroid genera are recognized and assigned to two families . four genera are gondwanan , three of these (
in all existing genera the ambulacral plates fuse in pairs early in life to form median articulating joints , termed vertebrae , and the ambulacral groove is converted into an internal epineural canal . these characters sharply distinguish extant ophiuroids from other asterozoa , but they are lacking from the more generalized palaeozoic ophiuroids .
subphylum asterozoa fossil and living forms ( lower ordovician about 500 , 000 , 000 years ago to recent ) ; radially symmetrical with more or less star - shaped body resulting from growth of arms in 1 plane along 5 divergent axes ; central mouth ; 5 arms ; dorsal tube feet and mouth . class stelleroidea features…
the representatives of asterozoa ( asteroidea , echinoidea , and ophiuroidea ) have a similar structural plan of the axial complex with minor differences within each class ; this structural scheme substantially differs from that in crinozoa and holothurozoa . the axial complex consists of the coelomic organs and the haemocoel ( blood ) structures , which are morphologically and functionally integral . the coelomic organs are the stone canal , axial coelom , perihaemal coeloms ( axocoel perihaemal ring and somatocoel perihaemal ring ) , water ring , and pericardial and genital coeloms . these organs are closely associated with the epigastric and hypogastric coeloms and with the perioral coelomic ring . the haemocoel structures of the axial complex include the oral haemal ring , heart , axial organ , genital haemal ring , and gastric haemal ring . the epineural canals of echinoids and ophiuroids are of a noncoelomic nature . they are formed by the invagination of the ectoneural cord and closing of the epidermis above it . the possible functions of the axial complex in asterozoa are blood circulation and excretion .
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cladogram based on arguments from spencer and wright ( 1966 ) , mcknight ( 1975 ) , and blake ( 1982 ) .
somasteroids are flattened , fivefold radially symmetrical echinoderms that range in shape from that of a pentagon to that of a star with protruding arms . it appears that somasteroids were benthic marine animals that were filter - and / or detritus - feeders . despite their relatively rigid arm structure , somasteroids are thought to have been somewhat mobile and able to scavenge along the ocean floor ( spencer , 1951 ) .
figure modified from fell ( 1963b ) . drawing by h . b . fell . copyright © 1963 royal society of london .
figure 2 . reconstructed cross - section of one arm of chininanaster sp . ( chinianasteridae ) . figure modified from fell ( 1963b ) . drawing by h . b . fell . copyright © 1963 royal society of london .
radial water vessels extend the length of each arm within a radial channel formed by the recumbent ambulacral plates and give rise to numerous tube feet ( figure 2 ) . in somasteroids , the radial water vessel is often positioned at the oral - marginal junction of ambulacrals , as in asteroids , but can also be enclosed within the ambulacral plates , as in ophiuroids . tube feet branching from the radial water vessels are seated in broad basins that , in some species , also give rise to ampulae that extend into the body cavity through ambulacral pores . the jaw ossicles of somasteroids are differentiated with small mouth angle plates , in contrast to those of asteroids that lack odontophores ( mcknight , 1975 ) . buccal slits , which function primarily as respiratory structures in ophiuroids , may or may not have been present adjacent to the mouth frame in somasteroids .
discussions addressing somasteroid origins have certainly been a major point of contention through the years primarily because the intermediate forms that gave rise to the somasteroids are lacking from the fossil record ( blake and guensburg 1993 ; blake , 1994 ) . it seems most likely , however , that the somasteroids emerged from either a crinoid lineage ( fell , 1963 ; mooi and david , 2000 ) , or an edrioasteroid lineage ( paul and smith , 1984 ; smith 1988b ) .
informative evolutionary and phylogenetic analyses within somasteroidea have been quite difficult because the examination and characterization of the group has been somewhat limited . what is known about the diversification of somasteroids , however , is primarily derived from work on three lower ordovician families : chinianasteridae ( tremadoc - early arenig ) , villebrunasteridae ( tremadoc - early arenig ) , and archegonasteridae ( late arenig ) , as discussed by nichols ( 1962 ) , fell ( 1963 ) , and blake ( 1982 ) .
the first organized classification of somasteroidea was carried out by w . k . spencer ( 1951 ) . in his report , spencer describes some of the earliest asteroid and ophiuroid specimens ever found . in addition , he describes fossils of a third asterozoan group , the somasteroids , which occur not only contemporaneously with , but also prior to all recognizable asteroid and ophiuroid fossil forms . these findings are suggestive of a scenario in which all asterozoans arose from ancient somasteroid forms .
blake , d . b . 1982 . somasteroidea , asteroidea , and the affinities of luidia ( plasterias ) latiradiata . paleontology , 25 : 167 - 191 .
blake , d . b . 1994 . re - evaluation of the palasteriscidae gregory , 1900 , and the early phylogeny of the asteroidea ( echinodermata ) . j . paleont . 68 : 123 - 134 .
blake , d . b . 1998 . morphological characters of early asteroids and ophiuroids . echinoderms : san francisco , mooi and telford ( eds . ) , balkema , rotterdam .
blake , d . b . , guensburg , t . e . , 1993 . new lower and middle ordovician stelleroids ( echinodermata ) and their bearing on the origins and early history of the stelleroid echinoderms .
fell , h . b . 1962 . a surviving somasteroid from the eastern pacific ocean . science , n . y . 136 : 633 - 636 .
fell , h . b . 1963a . a new family and genus of somasteroidea . trans . r . soc . n . z . 3 : 143 - 146 .
fell , h . b . 1963b . the phylogeny of sea - stars . phil . trans . r . soc . lond . , ser . b 246 : 381 - 435 .
mooi , r . , david , b . 2000 . what a new model of skeletal homologies tells us about asteroid evolution . amer . zool . 40 : 326 - 339 .
nichols , d . 1962 . echinoderms . huchinson and co . , london .
paul , c . r . c . , smith , a . b . 1984 . the early radiation and phylogeny of echinoderms . biological reviews , 46 : 157 - 200 .
smith , a . b . 1988 . patterns of diversification and extinction in early paleozoic echinoderms . paleontology , 31 : 799 - 828 .
smith , a . b . , jell , p . a . 1990 . cambrian ederoasteroids from australia and the origins of starfishes . mem . queen . mus . 28 : 715 - 778 .
spencer , w . k . 1951 . early paleozoic starfish . phil . trans . r . soc . lond . , ser . b 235 : 87 - 129 .
spencer , w . k . , wright , c . w . 1966 . asterozoans , pp . s4 - s107 . in r . c . moore ( ed . ) , treatise in invertebrate paleontology , part u , echinodermata 3 . geological society of america and the university of kansas press , new york and lawerance .
after spencer , w . k . 1951 . early paleozoic starfish . phil . trans . r . soc . lond . , ser . b 235 : 87 - 129 .
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phylogenetic hypothesis of the asteroidea based on blake ( 1987 ) . these relationships , as well as intra - order relationships , are contentious and re - evaluation of asteroid phylogeny continues ( see discussion of phylogenetic relationships , below ) .
the asteroidea is one of the largest and most familiar classes within the phylum echinodermata . these animals , commonly known as sea stars or starfishes , form a diverse and speciose group . there are approximately 1600 extant species ( hyman 1955 ; clark 1977 ; clark and downey 1992 ) which are found throughout the world ' s oceans . following the classification of blake ( 1987 ) , these species are grouped into seven orders : brisingida , forcipulatida , notomyotida , paxillosida , spinulosida , valvatida and velatida .
like other echinoderms , asteroids are important members of many marine benthic communities . they can be voracious predators , having significant impacts on community structure . for example , paine ( 1966 ) used pisaster ochraceus to illustrate his concept of the role keystone species play in community ecology . the crown - of - thorns starfish , acanthaster planci , is particularly well - known because it can cause extreme detrimental effects to coral reefs , particularly during population outbreaks ( moran 1988 ) .
figure 1 : pisaster ochraceus and acanthaster planci , two asteroids of great ecological significance . pisaster image by sherry ballard , courtesy calphotos , copyright © 1999 california academy of sciences . acanthaster image copyright © borut furlan .
the controversial concentricycloidea ( a proposed sixth class of the echinodermata ; baker et al . 1986 , rowe et al . 1988 , pearse and pearse 1994 ) have been diagnosed as unusual asteroids ( smith 1988 , belyaev 1990 , janies and mooi 1999 ) . their relationship to other asteroid taxa is not well resolved , but alliances with species from the velatida and the forcipulatida have been proposed . the unique morphology of the concentricycloids makes it difficult to assign this group to the recognized asteroid orders and is cited as sufficient distinction for class recognition .
figure 2 : a typical starfish , asterias rubens , with tubefeet visible on the edge of the arm in the foreground . image copyright © 2004 kåre telnes . cushion stars , like this culcita novaeguineae , may have arms so short that they look more like a ball than a star . image copyright © 2003 massimo boyer .
taxonomy of asteroids usually is based on externally observable characteristics of the skeleton , particularly the primary ossicular series which define the body wall ( ambulacrals , adambulacrals , marginals , terminals , actinals , abactinals ) , as well as secondary ossicles such as spines , spinelets and pedicellariae . works by perrier ( 1884 ) and sladen ( 1889 ) laid the taxonomic foundation of most asteroid groups . many other authors have contributed to and / or refined the asteroid classification scheme , notably fisher ( 1911 , 1928 ) , verrill ( 1914 ) , fell ( 1963 ) , spencer and wright ( 1966 ) and mcknight ( 1975 ) . blake and elliot ( 2003 ) provide clear definition of ossicle terminology . blake ( 1987 ) provides classification and diagnoses of asteroid groups .
figure 3 : morphology of asteroids . a , aboral and oral surfaces of a generalized asteroid . image © biodidac . b , transverse section and perspective view of a generalized arm ( soft tissues and spines removed ) ; note the arched ambulacral ossicles forming the ambulacral groove and the dorsal podial pores between ambulacral ossicles . one podium ( tubefoot ) on the left is drawn in outline only to illustrate how the podia descend through the podial pores . image © 2004 emily knott .
application of the extraxial - axial theory ( eat ) to asteroid morphology significantly aids our understanding of ossicle homologies within the asteroidea and between asteroids and other echinoderms ( mooi and david 2000 , blake and elliot 2003 , blake and hagdorn 2003 ) . according to the eat , the ambulacral and terminal ossicles of asteroids are axial elements . these ossicles are formed according to the ocular plate rule ( opr ) and are associated with the developing water vascular system during ontogeny as are the axial ossicles of other echinoderms . the remaining asteroid ossicle series are extraxial elements , which can be added during ontogeny without any particular ordering system ( although secondarily ordered serial homologous elements are common in the asteroids , e . g . adambulacrals and marginals ) . in comparison to axial elements , extraxial ossicles are prone to much more evolutionary lability ( mooi and david 1997 ) .
summarized from blake ( 1998 ; 2000 ) , mooi and david ( 2000 ) and blake and hagdorn ( 2003 ) .
deep ambulacral groove—the paired ambulacral ossicles are erect and arch across the arm axis forming a clearly defined furrow . the extent of the arch and definition of the furrow are expected to be weaker in the earliest asteroids , but these characters are difficult to observe in most fossil specimens .
dorsal podial pores—the dorsal podia pores are passageways between ambulacral ossicles through which the tubefeet descend . these pores allow for internal protection of the ampullae , dorsal outpockets of the podia , which contract and expand with extension and retraction of the podia . the ampullae of earlier asteroids were external , in closed , cup - like podial basins formed by the ossicles of the ambulacral column .
offset positioning of the ambulacral and adambulacral ossicles and differentiation of articulation structures in ossicles of the ambulacrum—these features describe a variety of related apomorphic characteristics of ambuloasteroids . offset positioning of the ambulacral and adambulacral ossicles allows for soft tissue connections between the ambulacral and both adjacent adambulacrals which is further enhanced with differentiation of articulation structures on the ossicles . this arrangement allows more complex movement in the ambuloasteroids . in non - ambuloasteroids a single ambulacral ossicle abuts a single adambulacral .
presence of an odontophore—the odontophore is a small interradial ossicle associated with the mouth angle ossicle . the odontophore is expected to the homologue of the axillary in paleozoic asteroids .
the earliest asteroids appeared in the ordovician ( figure 4 ) . however , at least two major faunal transitions have occurred within the asteroidea concomitantly with large extinction events : in the late devonian ( blake and glass in webster et . al . 1999 ) and in the late permian ( blake 1987 , gale 1987 , blake et al . 2000 , blake and elliot 2003 , blake and hagdorn 2003 ) . the asteroid orders as described here contain all extant and some extinct species which have a morphology distinct from paleozoic forms ( i . e . ambuloasteroidea ; see characteristics , blake 1982 , 1987 , 1988 ; gale 1987 , blake and elliott 2003 , blake and hagdorn 2003 ) . the asteroid orders are thought to have appeared and diversified very rapidly ( within approximately 60 million years ) during the lower and early middle jurassic , frustrating our understanding of ordinal relationships ( see discussion below ) .
figure 4 : hudsonaster sp . ( usnm 40882 ) , an early asteroid from the ordovician . image copyright © daniel b . blake
relationships among paleozoic asteroids , as well as between paleozoic asteroids and extant asteroids , are difficult if not impossible to determine because of the limitations of the asteroid fossil record . asteroid fossils are rare because 1 ) the skeletal elements rapidly dissociate after death of the animals 2 ) asteroids typically have a large body cavity that collapses with deterioration of the organs , resulting in misshapen forms and 3 ) asteroids often live on hard substrates which are not conducive to fossil formation . from the limited fossil evidence that is available we know that the basic body plan of the asteroids has remained the same since the ordovician . several papers by blake ( e . g 1989 , 2000 ) describe limitations of the fossil record in detail .
figure 5 : early neoasteroids from the triassic . images copyright © daniel b . blake
left : trichasteropsis weissmanni ( mhi 843 / 1 ) , trichasteropsida . center : trichasteropsis weissmanni ( smns 3173 / 5 ) , trichasteropsida . right : noriaster barberoi ( mpum 8420 ) , valvatida : poraniidae
a survey of asteroid nomenclature arranged by order has been compiled . clark ( 1989 , 1993 , 1996 ) and clark and mah ( 2001 ) list accepted names as well as synonyms , otherwise invalid names , references and ranges of type localities .
brisingida— brisingids are deep - sea dwelling asteroids . they usually have many ( 6 - 16 ) long , attenuated arms which are used in suspension feeding . the brisingida contains about 100 species in 17 genera and 6 families . a preliminary phylogeny for this order has been produced by mah ( 1998 ) .
forcipulatida— these asteroids are distinguished by their forcipulate pedicellariae , which are generally quite conspicuous on the body surface . the forcipulatida contains about 300 species in 68 genera and 6 families . a preliminary phylogeny for this order has been produced by mah ( 2000 ) .
notomyotida— these are deep - sea dwelling asteroids having flexible arms with characteristic longitudinal muscle bands along the inner dorsolateral surface . the notomyotida contains about 75 species in 12 genera and 1 family .
paxillosida— these asteroids are considered to be somewhat infaunal in that they can bury themselves partially under sandy sediments . they are characterized by some morphological features ( e . g . pointed , unsuckered tubefeet ) which have been considered primitive by some ( see discussion of phylogenetic relationships , below ) . the paxillosida contains about 255 species in 46 genera and 5 families .
spinulosida— these asteroids have a relatively delicate skeletal arrangement and completely lack pedicellariae . no fossil spinulosids have been found . the spinulosida contains about 120 species in 9 genera and 1 family .
valvatida— these asteroids are quite diverse , but are often characterized by their conspicuous marginal ossicles . definition of this group has been the most variable and the ordinal definition of many families included here has been controversial ( see discussion of phylogenetic relationships , below ) . the valvatida contains about 695 species in 165 genera and 14 families .
velatida— these asteroids typically have thick bodies with large discs and interradial depressions . contrary to blake ' s ( 1987 ) classification , molecular evidence suggests a relationship between some velatid and valvatid families ( see discussion of phylogenetic relationships , below ) . the velatida contains about 200 species in 25 genera and 5 families .
specific use of phylogenetic methods in studies of asteroid evolutionary relationships began in the late 1980s . these analyses ( using both morphological and molecular data ) have resulted in conflicting hypotheses of asteroid phylogeny . phylogenetic analyses are continuing to be re - evaluated with additional data . since their results are still somewhat contentious , they have yet to initiate changes in our classification system .
in 1987 , two differing hypotheses of order level relationships were proposed based on analyses of morphological characteristics ( blake 1987 , gale 1987 , figure 6 , 7 ) . these two phylogenies differ due to differences in opinion about character polarity ( assigning ancestral or derived status to a particular state of a character ) and the different morphological characters used in the analyses ( note that gale does not specifically use phylogenetic methods ) . both authors emphasized the importance of ambulacral characters to asteroid classification and recognized the distinction between paleozoic and post - paleozoic forms ( i . e . ambuloasteroidea , blake and hagdorn 2003 ) .
however , gale ( following mcknight 1975 ) focuses on the lack of suckered tubefeet in the paxillosida , considering them primitive . as a result , his phylogeny reflects two major groups : a basal paxillosida and the remaining asteroids , all having suckered tubefeet , which he termed superorder surculifera . blake considers suckered tubefeet to be the ancestral condition . his phylogeny reflects two major asteroid groups : superorder forcipulatacea ( forcipulatida + brisingida ) and a clade of the superorders valvatacea + spinulosacea ( valvatida , notomyotida , paxillosida , spinulosida and velatida ) . outgroup comparison with calliasterella and inclusion of the trichasteropsida results in a basal forcipulatacea .
the differences in these proposed phylogenies highlight questions about asteroid relationships that are still unresolved . the identification of the basal ( neo ) asteroid group has been the driving question of additional studies ( see evidence from molecular characters , below ) . additionally , ordinal definition , particularly for blake ' s valvatida , velatida and spinulosida , is problematic . such problems were not new to blake and gale . although many asteroid groups can be clearly defined morphologically ( forcipulatida , brisingida , notomyotida ) , asteroid morphology is complex and diverse . other groups are less clearly defined .
additional phylogenetic analyses incorporating molecular data with morphological data ( lafay et al . 1995 ) and using molecular data alone ( wada et al . 1996 ; knott and wray 2000 ) were presented in an effort to resolve phylogenetic arguments . unexpectedly , these studies have done little to elucidate asteroid relationships and may have only added to the confusion .
lafay et al . ( 1995 ) present an unrooted phylogeny deduced from analysis of a combined morphological data set taken from blake ( 1987 ) and gale ( 1987 ) with unordered character states ( figure 8 ) . although very few taxa were studied , their phylogeny supports the definition of asteroid orders proposed by blake but separates the paxillosida from the valvatida . their analysis with molecular data alone ( sequence data from 28s rrna ) results in several conflicting topologies due to weak phylogenetic signal . most of this signal is masked by that from the morphological data set when the two data sets are combined . however , after evaluating several rooting positions using molecular data from other echinoderms in outgroup comparison , lafay et al . ( 1995 ) conclude that the paxillosida may not be monophyletic and that the paxillosid genus astropecten may be the sister group to the remaining asteroids , reminiscent of gale ' s phylogeny .
wada et al . ( 1996 ) include more taxa for additional investigation of ordinal monophyly ( figure 9 ) . in multiple analyses of their molecular data set ( sequence data from 12s and 16s rdna ) , they find that paxillosids are paraphyletic with the paxillosid genus luidia as the basal asteroid taxon . in addition , the valvatida is not monophyletic and a forcipulatid clade falls within a group of valvatids , a velatid and spinulosids , a relationship in stark contrast to that proposed by blake ( 1987 ) . further , the spinulosida are never grouped with the velatida , which blake ( 1987 ) proposed as their sister group and which previously were considered a group within the spinulosida ( spencer and wright 1966 , mcknight 1975 , blake 1981a ) .
knott and wray ( 2000 ) expand taxon sampling even more , but their molecular data set ( sequence data from mitochondrial trna and coi genes ) fails to resolve questions of asteroid phylogeny ( figure 10 ) . significantly , the paxillosida is not basal in their results ( although astropecten is not included ) . the results of different tree reconstruction methods are not in agreement , and basal groupings are only supported by bootstrapping in the neighbor - joining analysis . the proposed phylogeny is similar to blake ( 1987 ) in that two lineages ( one largely of forcipulatids and the other largely of valvatids ) are recovered , but valvatida and velatida are not monophyletic and some velatids plus the spinulosida fall in the forcipulatid clade .
figure 8 . lafay et al . ' s ( 1995 ) hypothesis of asteroidea relationships .
figure 9 . wada et al . ' s ( 1996 ) hypothesis of asteroidea relationships .
figure 10 . knott & wray ' s ( 2000 ) hypothesis of asteroidea relationships .
baker , a . n . , f . w . e . rowe and h . e . s . clark . 1986 . a new class of echinodermata from new zealand . nature 321 : 862 - 864 .
belyaev , g . m . 1990 . is it valid to isolate the genus xyloplax as an independent class of echinoderms ? zoologicheskii zhurnal 69 : 83 - 96 .
blake , d . b . 1982 . recognition of higher taxa and phylogeny of the asteroidea . pp . 105 - 107 . in : international echinoderm conference , tampa bay . j . m . lawrence , ed . a . a . balkema , rotterdam .
blake , d . b . 1987 . a classification and phylogeny of post - paleozoic sea stars ( asteroidea : echinodermata ) . journal of natural history 21 : 481 - 528 .
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blake , d . b . 1998 . morphological characters of early asteroids and ophiuroids . pp . 5 - 8 . in : echinoderms : san francisco . proceedings of the ninth international echinoderm conference . r . mooi and m . telford , eds . a . a . balkema , rotterdam .
blake , d . b . 2000 . the class asteroidea ( echinodermata ) : fossils and the base of the crown group . american zoologist 40 : 316 - 325 .
blake , d . b . and d . r . elliott . 2003 . ossicular homologies , systematics and phylogenetic implications of certain north american carboniferous asteroids ( echinodermata ) . journal of paleontology 77 ( 3 ) : 476 - 489 .
blake , d . b . and h . hagdorn . 2003 . the asteroidea ( echinodermata ) of the muschelkalk ( middle triassic of germany ) . paläontologische zeitschrift 77 ( 1 ) : 23 - 58 .
blake , d . b . , a . tintori and h . hagdorn . 2000 . a new , early crown - group asteroid ( echinodermata ) from the norian ( triassic ) of northern italy . rivista italiana di paleontologia e stratigrafia . 106 ( 2 ) : 141 - 156 .
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clark , a . m . 1989 . an index of names of recent asteroidea : part 1 . paxillosida and notomyotida . pp . 225 - 347 in : echinoderm studies vol . 3 . m . jangoux and j . m . lawrence , eds . a . a . balkema , rotterdam .
clark , a . m . 1993 . an index of names of recent asteroidea : part 2 . valvatida . pp . 187 - 366 in : echinoderm studies vol . 4 . m . jangoux and j . m . lawrence , eds . a . a . balkema , rotterdam .
clark , a . m . 1996 . an index of names of recent asteroidea : part 3 . velatida and spinulosida . pp . 183 - 250 in : echinoderm studies vol . 5 . m . jangoux and j . m . lawrence , eds . a . a . balkema , rotterdam .
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horse , ( equus caballus ) , a hoofed , herbivorous mammal of the family equidae . it comprises a single species , …
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of projecting rays and a star - shaped body . it contains the one class stelleroidea .
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telford mj 1 , lowe cj 2 , cameron cb 3 , ortega - martinez o 4 , aronowicz j 5 , oliveri p 6 , copley rr 7 .
department of genetics , evolution and environment , university college london , darwin building , gower street , london wc1e 6bt , uk m . telford @ ucl . ac . uk .
hopkins marine station , department of biology , stanford university , 120 oceanview boulevard , pacific grove , ca 93950 , usa .
départment de sciences biologiques , université de montréal , pavillion marie - victorin , c . p . 6128 , succ . centre - ville , montréal , québec , canada h3c 3j7 .
department of biological and environmental sciences , sven lovén centre for marine sciences , university of gothenburg , kristineberg 566 , fiskebäckskil 451 78 , sweden .
department of organismal biology and anatomy , university of chicago , chicago , il 60650 , usa .
department of genetics , evolution and environment , university college london , darwin building , gower street , london wc1e 6bt , uk .
cnrs , laboratoire de biologie du développement de villefranche - sur - mer ( lbdv ) , observatoire océanographique , villefranche - sur - mer 06230 , france sorbonne universites , upmc univ paris 06 , laboratoire de biologie du developpement de villefranche - sur - mer , observatoire oceanographique , villefranche - sur - mer 06230 , france copley @ obs - vlfr . fr .
pmid : 24850925 pmcid : pmc4046411 doi : 10 . 1098 / rspb . 2014 . 0479
the two hypotheses of echinoderm evolution discussed in this work . the asterozoan hypothesis unites ophiuroids and asteroids on the basis of a five - rayed body plan . the cryptosyringid hypothesis places ophiuroids as sister group to the holothurians and echinoids on the basis of , for example , closed ambulacral grooves ( see introduction ) .
results from our data stratified by overall length of gene trees ( gene rate ranking ) , from ( a ) , the slowest evolving quartile , to ( d ) the fastest evolving quartile .
research support , u . s . gov ' t , non - p . h . s .
a subphylum of echinoderms characterized by a star - shaped body and radially divergent axes of symmetry .
subphylum expresses the vtg protein , vtg1 ( prowse and byrne , 2012 ) .
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data availability : the raw reads and assembled trasncriptomes reported in this paper have been deposited in the genbank database ( ncbi bioproject no . prjna236087 ) . assembly statistics and agalma resource reports can be found at : urltoken . see also urltoken .
funding : this work was funded by the national science foundation ios - 1120972 ( gw ) ; national institutes health 2r01hd028152 ( gw ) ; national institutes health 5t32 gm007601 ( ar ) . the funders had no role in study design , data collection and analysis , decision to publish , or preparation of the manuscript .
most phylogenetic studies place echinoidea and holothuroidea as sister groups . the difficulty lies in the placement of ophiuroidea ; different methods favor different positions for brittle stars . a ) the predominant hypotheses of how extant echinoderms are related are the asterozoan and cryptosyringid hypotheses . b ) two other alternate hypotheses based on mitochondrial gene alignments .
whole ovary was dissected from gravid females and placed in trizol ( invitrogen ) . rna was extracted and then cleaned with a qiagen rneasy micro column with on - column dna digestion . the sequencing libraries were prepared with illumina reagents , ( mrna - seq sample prep kit for gaiix samples or truseq sample prep kit for hiseq samples ) with the maximum recommended rna input . the protocol was followed exactly with the addition of a gel selection step of 400–500bp , ( agarose gel for gaiix samples or caliper labchip xt for hiseq samples ) prior to pcr amplification .
all 30 datasets ( 23 de novo assembled transcriptomes and 7 refseq datasets ; s1 table ) were compared against ncbi swissprot using blastx with a cutoff of 0 . 000001 [ 23 ] . transdecoder was used to translate sequences , and similar translated sequences were identified by a pair wise blastp followed by clustering using mcl [ 32 ] to identify orthologous genes . two supermatricies that differ in gene sampling were used in the phylogenetic analyses : ‘sparse’ and ‘dense’ . the ‘sparse’ supermatrix has all 30 taxa and 34 % matrix occupancy , ( s4a fig . ) with 4 , 645 peptide sequences and 630 , 945 amino acid sites . the ‘dense’ supermatrix is a subset of the sparse matrix . it has all 30 taxa and 70 % matrix occupancy , ( s4b fig . ) with 1 , 125 peptide sequences and 101 , 652 amino acid sites . maximum likelihood phylogenetic analyses were done with raxml ( gammawag model ) with 1 , 000 boot strap iterations on the ‘dense’ supermatrix , and using the same model , 100 boot strap iterations on the ‘sparse’ supermatrix . both supermatrices and calculated phylograms can be downloaded from the data dryad repository [ 33 ] .
baysian phylogenetic analyses were done with phylobayes 1 . 3b - mpi [ 34 ] on the ‘dense’ supermatrix using the cat - gtr model with the following command : “pb _ mpi - s - d supermatrix . dense . phylip - cat - gtr outputfile” . a total of 31 , 623 generations were run over three chains . all three chains converged within 2 , 000 generations ( s5 fig . ) and after removing these 2 , 000 from each chain and sampling every 10 trees , the maximum difference was 1 . 17×10 - 3 , ( 2 , 561 sampled trees ) , and a majority consensus tree was constructed .
the sowh test was implemented using the sowhat software package , [ 35 ] ( urltoken ) with the following command : “perl sowhat—constraint = alternate . hypo . tre—aln = supermatrix . dense . phylip—model = protgammawag—dir = outdir—name = outfile—rax = ' raxmlhpc - pthreads - sse3 - t 16 ' —seqgen = seq - gen—reps = 500—stop > output . txt” . three alternate hypothesis trees were constructed to test : a ) the cryptosyringid hypothesis , b ) ophiuroidea sister to the rest of echinoderms , and c ) asteroidea sister to echinozoa ( s3 fig . ) . all three analyses were stopped after at least 99 iterations because any additional sampling was very unlikely to change the results ( s3 fig . ) .
the raw reads and assembled trasncriptomes reported in this paper have been deposited in the genbank database ( ncbi bioproject no . prjna236087 ) . assembly statistics , agalma resource reports and scripts used in the analyses can be found in the git repository [ 25 ] and the supermatrix alignments and all trees including sowh constraint trees can be downloaded from the dryad digital repository [ 33 ] . all de novo transcriptomes can also be accessed on echinobase . org , including blast searches of the annotated transcripts .
the assembly of the de novo illumina transcriptomes yielded on average 24 , 033 high quality contigs with a match to swissprot ( s1 table ) . the number of transcripts with swissprot hits in the de novo transcriptomes was comparable to the number of sequences in the refseq datasets we included for other taxa ( s1a fig . ) . the number of swissprot sequences did not appear to be artificially inflated by fragmented assemblies ( s1b fig . ) . the comparable number of swissprot sequences and comparable size of the n50s of the de novo transcriptomes in relation to the refseq datasets both suggest that the assembled transcriptomes are of high quality ; especially compared with the s . purpuratus refseq dataset , an echinoderm with a well sequenced and annotated genome [ 8 ] .
support values for the phylogenetic trees using raxml and phylobayes on the dense and sparse supermatricies . each node is scored with three support values ; an asterisk denotes 100 / 100 / 100 support . the first support value is the dense supermatrix raxml 1 , 000 bootstraps , the second value is the sparse supermatrix raxml 100 bootstraps , and the third value is the dense supermatrix phylobayes posterior probabilities . the phylogram presented here is from the dense supermatrix raxml analysis . see s2 fig . for the tree topology predicted by the phylobayes analysis .
the size of data matricies and their occupancy has varied considerably over recent phylogenomic studies , which have differed substantially in the sequencing technologies used as well as methods for identification of orthologous genes and matrix construction . the present study uses a similar matrix construction technique as previous analyses [ 31 ] , but the occupancy of the matrix is much higher . this suggests that at least part of the reason for reduced occupancy in some previous analyses was due to data acquisition , and that future studies based entirely on the most recent sequencing technologies will have much improved gene sampling .
overall , the present study provides the greatest depth and breadth of new sequence analysis for consideration of the phylogenetic relationships of echinoderms . coupled with the recent study using 219 genes for analysis from four newly sequenced echinoderms [ 18 ] , and of a broader analysis of ambulacraria using 185 genes , including six newly sequenced echinoderms [ 24 ] , mostly non - overlapping tissues and animals from the present work , we now have a rich analysis to present . since each these studies used different animals , different methodology of analysis , and different depths of data consideration , yet they each came to the same conclusions in regards to the major echinoderm taxon relationships , we now have great confidence in the relationships of these animals and provide deep datasets for further analysis .
s1 fig . histograms of the postassembly comparisons of refseq and de novo assembled datasets .
( a ) the numbers of swissprot transcripts is comparable between refseq datasets ( green and purple ) and de novo assembled transcriptomes ( orange ) . ( b ) comparing the n50 of the swissprot transcripts , the de novo transcriptomes are on average only slightly smaller than the refseq datasets . the s . purpuratus refseq dataset is in purple , outgroup refseq datasets in green and de novo assembled transcriptomes in orange ; colours as in s1 table . the number of transcriptomes is on the ordinate axis .
support values for the phylogenetic trees using raxml and phylobayes on the dense and sparse supermatricies . each node is scored with three support values ; an asterisk denotes 100 / 100 / 100 support . the first support value is the dense supermatrix raxml 1 , 000 bootstraps , the second value is the sparse supermatrix raxml 100 bootstraps , and the third value is the dense supermatrix phylobayes posterior probabilities . the phylogram presented here is from the dense supermatrix phylobayes analysis .
the sowh tests were run for at least 99 iterations on the dense supermatrix and were stopped because any further iterations were unlikely to change . the three sowh tests used the following tree topologies to test : ( a ) the crytosynirgid hypothesis , ( ( sea urchins , sea cucumbers , brittle stars ) , ( sea stars , feather star , outgroups ) ) ; , ( b ) ophiuroidea sister to the rest of echinoderms , ( ( sea urchins , sea cucumbers , sea stars , feather star ) , ( brittle stars , outgroups ) ) ; , and ( c ) asteroidea sister to echinozoa ( ( sea urchins , sea cucumbers , sea stars ) , ( brittle stars , feather star , outgroups ) ) ; . none of the three tests found support for any alternate hypothesis with p - values all equal to 0 .
s4 fig . visual representation of the sparse and dense supermatricies including all thirty taxa .
each horizontal row is a single taxa and each vertical column is a gene alignment ; presence is marked in black and absence in white . the taxa are arranged from top to bottom from most genes present to least . ( a ) the sparse supermatrix is 34 % occupied , contains all 30 taxa , and contains alignments of 4 , 645 peptide sequences . ( b ) the dense supermatrix is 70 % occupied , contains all 30 taxa , and contains alignments of 1 , 125 peptide sequences .