BACKGROUND
annelida, the segmented worms , are distributed worldwide from the deepest marine sediments to freshwater and soil habitats.
throughout most of the 20th century they were split into three or four major groups, polychaeta, myzostomida, oligochaeta and hirudinea.
it is now widely recognized that oligochaeta and hirudinea form a clade that is referred to as clitellata .
several interstitial groups were classified as the "archiannelida", another annelid group; however, they are now generally regarded as secondarily simplified, possibly progenetic polychaetes  <cit> .
several more groups have been hypothesized to belong into the annelida  <cit> , and there is a growing consensus that the echiurida, pogonophora , and sipunculida are actually modified annelids  <cit> .
a cladistic analysis of annelida, based on morphological characters, has resulted in a new classification  <cit> , with three major clades of the polychaeta: scolecida, aciculata , and canalipalpata .
however, several annelid groups were left outside this classification.
they include clitellata, the freshwater and/or terrestrial "clitellate-like" worms , some "archiannelids" , and psammodrilidae.
from a molecular perspective, the sequence datasets assembled to date have usually been marked by limited numbers of both taxa and characters.
almost all annelid families are now represented by the nuclear small-subunit ribosomal rna genes ; unfortunately, even 18s studies using the densest taxon sampling  <cit>  were unable to recover a monophyletic annelida or its major subclades.
even if several genes are concatenated to reconstruct annelid phylogeny in recent papers, none of the morphology-based higher taxa  were recovered  <cit> .
recent papers by struck et al.
<cit>  provided the first molecular trees with several resolved higher taxa of the annelida.
they included aciculata , phyllodocida , terebelliformia, sabellida-spionida, cirratuliformia, and amphinomida.
synthesis of molecular and morphological data from extant and potentially also extinct taxa remains the strongest test of phylogenetic hypotheses and the best summary of the common signal in the diverse data available for phylogenetics  <cit> .
the "total-evidence" analyses have been published for a few annelid taxa, viz., clitellata  <cit> , terebelliformia  <cit> , most canalipalpata  <cit> , aphroditiformia  <cit> , and most aciculata  <cit> .
so far, no attempt has been made to analyse simultaneously morphological and molecular information on the annelida as a whole.
in this paper we present the first comprehensive analysis of higher-level phylogenetic relationships in annelida based on combined morphological and molecular  data.
the purpose is to identify stable and ustable nodes of the combined annelid tree, to make up reliable phylogenetic hypothesis on annelida, and thus test the morphology-based classification.
RESULTS
the congruence of data partitions
the combined data matrix included  <dig> terminals and  <dig>  cladistically informative characters .
out of  <dig>  data matrix cells , 6% were polymorphic and 30% were missing .
distribution of the ambiguous character states is highly uneven, as four terminals  are represented by two data partitions only .
evaluation of the relative quality of data partitions and their performance in the combined maximum-parsimony analysis indicated that the mor dataset was highly influential in the simultaneous analyses of all data partitions .
the partitioned bremer support  values in the combined dataset, limited to the  <dig> composite terminals that were represented by all seven data partitions , revealed that despite the significant incongruence of the morphological and molecular data partitions, the former contributed positively to bremer support values of   <dig> clades  and is negative for  two clades  only: one within terebelliformia, the other concerning position of the orbiniidae within aciculata.
the molecular partitions analysed together are in conflict with two clades as well, both concerning the placement of the amphinomidae as a sister group of the eunicida.
the molecular partitions are, however, by no means homogeneous.
the pbs analysis showed that four data partitions contributed positively to the combined-tree topology , while the other three molecular partitions  are in conflict with the combined tree.
bayesian  tree
in the combined bi tree, the basal relationships were not fully resolved.
however, there were several well-supported  clades :  the "sabelloid-spionoid clade" ;  cirratuliformia ;  fauveliopsidae-paraonidae-cossuridae;  clitellata-aphanoneura-hrabeiella ;  pogonophora;  opheliidae-scalibregmatidae;  the "terebelloid-capitelloid clade" or "tcc" ;  phyllodocida;  eunicida;  the "orbinioid-parergodrilid clade" or "opc";  aberranta-amphinomida; and  the "core archiannelida" .
the traditional aciculata and canalipalpata roughly corresponded to the two major superclades .
the "aciculata" included phyllodocida, eunicida, and opc.
the "canalipalpata" included ssc, sternaspis, tcc, cirratuliformia, fauveliopsidae-paraonidae-cossuridae, pogonophora, and also "clitellatomorpha" and opheliidae-scalibregmatidae.
there were, in addition, several groups outside the two major sister superclades: oweniidae, chaetopteridae, magelona, myzostomida-protodriloides, aberranta-amphinomida, apistobranchus-dinophilidae-sipunculida, and the "core archiannelida".
maximum-parsimony  trees
in the unweighted  analysis , monophyletic aciculata were nested within paraphyletic "canalipalpata" .
a few taxa seemed to be misplaced due to long-branch artifacts ; moreover, there was an obviously artifactual "basal" clade including "archiannelids", myzostomids, and several long-branch aciculatans and canalipalpatans.
the weighted  tree  was nearly identical with the bi tree .
they differed predominantly only in position of the opheliidae-scalibregmatidae clade, "core archiannelids", dinophilidae-sipunculida clade, apistobranchus, and tomopteridae.
taxon-exclusion tests
the preliminary results suggested that ingroup and outgroup taxon selection affected internal relationships.
to highlight topological problems in placement of the most "problematic" taxa , several experimental analyses were performed.
in the taxon-exclusion tests, after removing the "problematic" species/clades, the unrooted "backbone trees" were almost identical irrespective of the used methods .
both included either monophyletic or paraphyletic  "aciculata" and "canalipalpata", and differed only in the specific position of the pogonophora-"clitellatomorpha" clade within the "canalipalpata" .
the important "problematica" grouped consistently as follows: oweniidae as a sister group of the pogonophora; fauveliopsidae, magelona, and opheliidae-scalibregmatidae within the cirratuliformia-ssc clade; apistobranchus as a sister group of opc; and aberranta-amphinomida next to  the phyllodocida.
the other "problematic species" were placed at more or less conflicting positions in bi and ump tests .
the ougroups tended to be placed within the "canalipalpata", close to the pogonophora and/or "clitellatomorpha".
discussion
the present analysis points out instability of some basal nodes within the annelid tree.
however, most analyses, irrespective of the used methods and parameter sets, converge to a highly compatible set of actually  monophyletic taxa.
they are  eunicida-opc;  phyllodocida;  ssc;  cirratuliformia;  tcc;  "clitellatomorpha"; and  pogonophora .
several morphology-based taxa like "scolecida" , "terebellida" , and "spionida"   <cit>  are definitely polyphyletic.
the most problematic issue is the tree root position.
the all-taxa analyses  supported that the root is situated between chaetopterids, magelonids, and/or oweniids and the rest of the annelida .
the experimental analyses  suggested that the non-annelid outgroups were placed next to the oweniidae, pogonophora, and/or "clitellatomorpha".
phyllodocida, eunicida, and the orbinioid-parergodrilid clade
the phyllodocida  is consistently a monophyletic group in all analyses, except for "basal" placement of the long-branch tomopteridae in some mp trees.
in all analyses, there is a strongly supported clade including monophyletic eunicida  and opc, corroborated by presence of the lateral/dorsal cirrus organs and larval akrotrochs.
however, the position of the lumbrinerids could be more basal, as they appeared as a sister group of the whole eunicida-phyllodocida in some purely molecular trees  <cit> .
the placement of the orbiniids among the aciculatans provides a strong phylogenetic support for the hypothesis that their aciculae are homologous with those of the euncida and phyllodocida  <cit> .
the sister-group relationship between parergodrilidae and orbiniidae-questa is strongly supported by all analyses  <cit> ; both groups share gonoducts with a distal glandular part  <cit> .
no closer orbiniid-spionidan relationships  <cit>  have been recovered by the present analyses.
also apistobranchus consistently grouped with opc in the taxon-exclusion analyses.
it is, therefore, possible that also the apistobranchus acicula-like chaetae  <cit>  might be actually true aciculae.
"terebelloid-capitelloid clade"
one of the most stable clade covers terebelliformia, capitellidae-echiurida and arenicolidae-maldanidae.
this clade is weakly supported morphologically, by the specific chaetal arrangement and by the presence of a gular membrane.
the placement of the terebelliformians close to a generally palpless group provides a phylogenetic support for the hypothesis that terebelliformian "buccal tentacles" are not homologous with the true polychaete palps  <cit> .
although classified as a separate phylum until recently, there is a growing consensus that echiurida is a subgroup of the annelida  <cit> , as they exhibit segmentation traits during ontogeny.
the explicit hypotheses about their specific position were published only by molecular phylogeneticists who discovered close relationships of the echiurida to the capitellidae  <cit> .
also the opheliidae and scalibregmatidae group either within tcc , or as an isolated clade .
however, in absence of all other problematic annelids, the opheliidae-scalibregmatidae clade nests close to the ssc.
"sabelloid-spionoid clade"  and cirratuliformia
in all trees, sabellidae, spionida s.str.
, and sabellariidae form a clade  <cit> .
the chaetal arrangement in sabellariidae has recently been dismissed as homologous to the sabellid-serpulid chaetal inversion pattern, and therefore provides no support for a sister-group relationship of sabellids and sabellariids with exclusion of the spionida s.str.
<cit> .
fauveliopsidae, sternaspis, cossuridae and paraonidae are consistently placed next to the ssc and/or cirratuliformia .
the monophyly of the "terebellida"  has never been found in the molecular and combined trees.
"clitellatomorpha"
phylogenetic position of the clitellata and most "clitellate-like" annelids is stable and quite surprising in the present analyses: they always form a clade, further split into clitellata and the hrabeiella-aphanoneura subclade.
this clade is supported by hermaphroditism, direct development, loss of parapodia, presence of the unbranched type of ciliary ocelli, metanephridial mantle cell, possibly also by the dorsal pharynx, and by primarily freshwater/soil habitats  <cit>  .
the intra-clitellate position of the aphanoneura was not supported by reliable morphological synapomorphies , and exclusion of aphanoneurans from the clitellata was also indicated by most previous molecular analyses  <cit> .
the recent molecular analyses, on the contrary, seem to corroborate close relationships between clitellata and  the "clitellate-like polychaetes"  <cit> .
the close relationships of the clitellata to some eunicidans or dinophilids  <cit> , or to tcc  <cit>  have never been found in the present analyses.
pogonophora and "basal canalipalpata"
in the present analyses, the pogonophora  is closely related to the "clitellatomorpha" or, in absence of the latter group, pogonophora alone groups as a sister group of ssc.
three groups of the traditional canalipalpata, namely, oweniidae, magelona, and chaetopteridae, were usually placed among the most basal annelids, or even outside the annelida, in the present all-species analyses  <cit> .
the taxon-exclusion analyses suggested that magelonids and oweniids might in fact be attracted strongly towards the remote annelid outgroups.
in absence of all other "problematic" annelids, oweniidae alone grouped consistently with the pogonophora , and magelona either with the paraonidae  or as a sister group of the cirratuliformia-ssc superclade .
on the contrary, basal placement of the chaetopteridae cannot be excluded  <cit> .
amphinomida and aberranta
in the most present analyses, aberranta is a sister group of the amphinomida, and the whole clade is one of the basalmost annelid branches, far from the other aciculata  <cit> .
however, in the taxon-exclusion tests, the aberranta-amphinomida clade  is placed as a sister group of the phyllodocida  or even within it .
it is then possible that the aberranta-amphinomida clade is, in fact, one of subgroups of the monophyletic aciculata  <cit> , misplaced in most molecular trees .
therefore, it seems rather premature to regard amphinomida as a basal group, "based on the tetraneurous organization of the nervous system"  <cit> ; moreover, the presence of several peripheral longitudinal nerves is not limited to the amphinomids  <cit> .
"core archiannelids"
monophyly of the "archiannelida" has been rejected by all modern authors  <cit> , whereas the monophyly of protodrilida  as well as its spionidan affinities has been proposed recently  <cit> .
the polygordiids were regarded as relatives of protodrilidans or of opheliids  <cit> , or as the canalipalpatans of uncertain position  <cit> .
surprisingly, the molecular trees tend to include a clade covering most of the traditional "archiannelids"  <cit> .
in the present all-taxa bi tree, there is a well-supported basal annelid clade including nerillidae-protodrilidae and polygordiidae-saccocirridae.
although nerillidae were considered aciculatans of uncertain position  <cit> , closer relationships of the nerillidae with any aciculata have never been retrieved in the present analyses.
in conclusion, it is an interesting working hypothesis that the "archiannelida"  might form a clade  <cit> , either basal, or close to the ssc  <cit> .
sipunculida and dinophilidae
the sipunculida have been considered a separate phylum by most authors  <cit> .
although they as adults do not exhibit any signs of segmentation, sipunculids show transitional stages of segmentation during development of their ventral nerve cord  <cit> .
analyses of the mitochondrial genomes  <cit>  as well as phylogenomics  <cit>  suggest that the sipunculids are an annelid ingroup.
the unique correspondence of podocyte lining the metanephridia appears to join sipunculida with the sabellida and terebelliformia  <cit> .
the pharyngeal apparatus in the sipunculid pelagosphere larvae is similar to that found in the cirratuliformia  <cit> .
in the present trees, the sipunculids have always been found as an annelid ingroup, often close to the dinophilidae.
no closer relationships between sipunculids and terebelliformians, sabellidans, oweniids or chaetopterids  <cit>  were recovered here.
the enigmatic dinophilidae were never found to be closely related to the dorvilleidae , i.e.
in the placement expected by the morphologists  <cit> .
even parapodrilus, one of the presumably dinophilid-related, "progenetic" dorvilleids  <cit> , groups consistently with other dorvilleids within the eunicida and shows no affinities to the dinophilidae  <cit> .
in the taxon-exclusion analyses, both dinophilidae and sipunculida group within the cirratuliformia , or they are a sister group of the pogonophora-"clitellatomorpha" superclade .
in conclusion, close affinities between dinophilidae and sipunculida  appear as a possible working hypothesis  <cit> , but the precise position of this clade remains uncertain.
myzostomida
relationships of the myzostomida, traditionally regarded as aberrant polychaetes, probably phyllodocidans  <cit> , are uncertain.
they may be either basal protostomes  <cit>  or platyzoan relatives  <cit> .
their highly aberrant sequences  and uncertain homology of many morphological characters do not allow to deduce their relationships precisely.
nevertheless, the numerous annelid-like traits of the myzostomida  <cit>  still could corroborate some polychaete-myzostomid proximity.
recently, bleidorn et al.
<cit>  re-examined this issue by analysis of four nuclear genes and a mitochondrial genome and showed myzostomids are likely part of the annelid radiation.
on the contrary, in the comprehensive phylogenomic analysis of the metazoa  <cit> , myzostomida are placed within the platyzoa .
in the present analyses, the myzostomids seem to belong into the annelida .
however, the taxon sampling in this paper does not provide a suitable test for alternative hypotheses due to lack of most of the possible non-annelid relatives of the myzostomida .
CONCLUSIONS
the combined  phylogenetic analysis provides a modified view of annelid evolution.
several higher-level annelid taxa are suggested by our analyses, i.e.
phyllodocida, eunicida, the orbinioid-parergodrilid clade, cirratuliformia, sabelloid-spionoid clade, terebelloid-capitellid clade , and "clitellatomorpha".
although the deep-level evolutionary relationships of annelida remain poorly understood, we propose sister-group relationships between the phyllodocida-aberranta-amphinomida and eunicida-opc clades, between the cirratuliformia and ssc, and possibly also between the "clitellatomorpha" and oweniidae-pogonophora clades.
two unorthodox clades, "core archiannelida" and dinophilidae-sipunculida, are proposed here.

 annelida, the segmented worms, are distributed worldwide from the deepest marine sediments to freshwater and soil habitats. throughout most of the 20th century they were split into three or four major groups, polychaeta, myzostomida, oligochaeta and hirudinea. it is now widely recognized that oligochaeta and hirudinea form a clade that is referred to as clitellata. several interstitial groups were classified as the "archiannelida", another annelid group; however, they are now generally regarded as secondarily simplified, possibly progenetic polychaetes. several more groups have been hypothesized to belong into the annelida, and there is a growing consensus that the echiurida, pogonophora, and sipunculida are actually modified annelids. a cladistic analysis of annelida, based on morphological characters, has resulted in a new classification, with three major clades of the polychaeta: scolecida, aciculata, and canalipalpata. however, several annelid groups were left outside this classification. they include clitellata, the freshwater and/or terrestrial "clitellate-like" worms, some "archiannelids", and psammodrilidae. from a molecular perspective, the sequence datasets assembled to date have usually been marked by limited numbers of both taxa and characters. almost all annelid families are now represented by the nuclear small-subunit ribosomal rna genes; unfortunately, even 18s studies using the densest taxon sampling were unable to recover a monophyletic annelida or its major subclades. even if several genes are concatenated to reconstruct annelid phylogeny in recent papers, none of the morphology-based higher taxa were recovered. recent papers by struck et al. provided the first molecular trees with several resolved higher taxa of the annelida. they included aciculata, phyllodocida, terebelliformia, sabellida-spionida, cirratuliformia, and amphinomida. synthesis of molecular and morphological data from extant and potentially also extinct taxa remains the strongest test of phylogenetic hypotheses and the best summary of the common signal in the diverse data available for phylogenetics. the "total-evidence" analyses have been published for a few annelid taxa, viz., clitellata, terebelliformia, most canalipalpata, aphroditiformia, and most aciculata. so far, no attempt has been made to analyse simultaneously morphological and molecular information on the annelida as a whole. in this paper we present the first comprehensive analysis of higher-level phylogenetic relationships in annelida based on combined morphological and molecular data. the purpose is to identify stable and ustable nodes of the combined annelid tree, to make up reliable phylogenetic hypothesis on annelida, and thus test the morphology-based classification.  the congruence of data partitions the combined data matrix included terminals and cladistically informative characters. out of data matrix cells, 6% were polymorphic and 30% were missing. distribution of the ambiguous character states is highly uneven, as four terminals are represented by two data partitions only. evaluation of the relative quality of data partitions and their performance in the combined maximum-parsimony analysis indicated that the mor dataset was highly influential in the simultaneous analyses of all data partitions. the partitioned bremer support values in the combined dataset, limited to the composite terminals that were represented by all seven data partitions, revealed that despite the significant incongruence of the morphological and molecular data partitions, the former contributed positively to bremer support values of clades and is negative for two clades only: one within terebelliformia, the other concerning position of the orbiniidae within aciculata. the molecular partitions analysed together are in conflict with two clades as well, both concerning the placement of the amphinomidae as a sister group of the eunicida. the molecular partitions are, however, by no means homogeneous. the pbs analysis showed that four data partitions contributed positively to the combined-tree topology, while the other three molecular partitions are in conflict with the combined tree. bayesian tree in the combined bi tree, the basal relationships were not fully resolved. however, there were several well-supported clades: the "sabelloid-spionoid clade"; cirratuliformia; fauveliopsidae-paraonidae-cossuridae; clitellata-aphanoneura-hrabeiella; pogonophora; opheliidae-scalibregmatidae; the "terebelloid-capitelloid clade" or "tcc"; phyllodocida; eunicida; the "orbinioid-parergodrilid clade" or "opc"; aberranta-amphinomida; and the "core archiannelida". the traditional aciculata and canalipalpata roughly corresponded to the two major superclades. the "aciculata" included phyllodocida, eunicida, and opc. the "canalipalpata" included ssc, sternaspis, tcc, cirratuliformia, fauveliopsidae-paraonidae-cossuridae, pogonophora, and also "clitellatomorpha" and opheliidae-scalibregmatidae. there were, in addition, several groups outside the two major sister superclades: oweniidae, chaetopteridae, magelona, myzostomida-protodriloides, aberranta-amphinomida, apistobranchus-dinophilidae-sipunculida, and the "core archiannelida". maximum-parsimony trees in the unweighted analysis, monophyletic aciculata were nested within paraphyletic "canalipalpata". a few taxa seemed to be misplaced due to long-branch artifacts; moreover, there was an obviously artifactual "basal" clade including "archiannelids", myzostomids, and several long-branch aciculatans and canalipalpatans. the weighted tree was nearly identical with the bi tree. they differed predominantly only in position of the opheliidae-scalibregmatidae clade, "core archiannelids", dinophilidae-sipunculida clade, apistobranchus, and tomopteridae. taxon-exclusion tests the preliminary results suggested that ingroup and outgroup taxon selection affected internal relationships. to highlight topological problems in placement of the most "problematic" taxa, several experimental analyses were performed. in the taxon-exclusion tests, after removing the "problematic" species/clades, the unrooted "backbone trees" were almost identical irrespective of the used methods. both included either monophyletic or paraphyletic "aciculata" and "canalipalpata", and differed only in the specific position of the pogonophora-"clitellatomorpha" clade within the "canalipalpata". the important "problematica" grouped consistently as follows: oweniidae as a sister group of the pogonophora; fauveliopsidae, magelona, and opheliidae-scalibregmatidae within the cirratuliformia-ssc clade; apistobranchus as a sister group of opc; and aberranta-amphinomida next to the phyllodocida. the other "problematic species" were placed at more or less conflicting positions in bi and ump tests. the ougroups tended to be placed within the "canalipalpata", close to the pogonophora and/or "clitellatomorpha". discussion the present analysis points out instability of some basal nodes within the annelid tree. however, most analyses, irrespective of the used methods and parameter sets, converge to a highly compatible set of actually monophyletic taxa. they are eunicida-opc; phyllodocida; ssc; cirratuliformia; tcc; "clitellatomorpha"; and pogonophora. several morphology-based taxa like "scolecida", "terebellida", and "spionida" are definitely polyphyletic. the most problematic issue is the tree root position. the all-taxa analyses supported that the root is situated between chaetopterids, magelonids, and/or oweniids and the rest of the annelida. the experimental analyses suggested that the non-annelid outgroups were placed next to the oweniidae, pogonophora, and/or "clitellatomorpha". phyllodocida, eunicida, and the orbinioid-parergodrilid clade the phyllodocida is consistently a monophyletic group in all analyses, except for "basal" placement of the long-branch tomopteridae in some mp trees. in all analyses, there is a strongly supported clade including monophyletic eunicida and opc, corroborated by presence of the lateral/dorsal cirrus organs and larval akrotrochs. however, the position of the lumbrinerids could be more basal, as they appeared as a sister group of the whole eunicida-phyllodocida in some purely molecular trees. the placement of the orbiniids among the aciculatans provides a strong phylogenetic support for the hypothesis that their aciculae are homologous with those of the euncida and phyllodocida. the sister-group relationship between parergodrilidae and orbiniidae-questa is strongly supported by all analyses; both groups share gonoducts with a distal glandular part. no closer orbiniid-spionidan relationships have been recovered by the present analyses. also apistobranchus consistently grouped with opc in the taxon-exclusion analyses. it is, therefore, possible that also the apistobranchus acicula-like chaetae might be actually true aciculae. "terebelloid-capitelloid clade" one of the most stable clade covers terebelliformia, capitellidae-echiurida and arenicolidae-maldanidae. this clade is weakly supported morphologically, by the specific chaetal arrangement and by the presence of a gular membrane. the placement of the terebelliformians close to a generally palpless group provides a phylogenetic support for the hypothesis that terebelliformian "buccal tentacles" are not homologous with the true polychaete palps. although classified as a separate phylum until recently, there is a growing consensus that echiurida is a subgroup of the annelida, as they exhibit segmentation traits during ontogeny. the explicit hypotheses about their specific position were published only by molecular phylogeneticists who discovered close relationships of the echiurida to the capitellidae. also the opheliidae and scalibregmatidae group either within tcc, or as an isolated clade. however, in absence of all other problematic annelids, the opheliidae-scalibregmatidae clade nests close to the ssc. "sabelloid-spionoid clade" and cirratuliformia in all trees, sabellidae, spionida s.str., and sabellariidae form a clade. the chaetal arrangement in sabellariidae has recently been dismissed as homologous to the sabellid-serpulid chaetal inversion pattern, and therefore provides no support for a sister-group relationship of sabellids and sabellariids with exclusion of the spionida s.str.. fauveliopsidae, sternaspis, cossuridae and paraonidae are consistently placed next to the ssc and/or cirratuliformia. the monophyly of the "terebellida" has never been found in the molecular and combined trees. "clitellatomorpha" phylogenetic position of the clitellata and most "clitellate-like" annelids is stable and quite surprising in the present analyses: they always form a clade, further split into clitellata and the hrabeiella-aphanoneura subclade. this clade is supported by hermaphroditism, direct development, loss of parapodia, presence of the unbranched type of ciliary ocelli, metanephridial mantle cell, possibly also by the dorsal pharynx, and by primarily freshwater/soil habitats. the intra-clitellate position of the aphanoneura was not supported by reliable morphological synapomorphies, and exclusion of aphanoneurans from the clitellata was also indicated by most previous molecular analyses. the recent molecular analyses, on the contrary, seem to corroborate close relationships between clitellata and the "clitellate-like polychaetes". the close relationships of the clitellata to some eunicidans or dinophilids, or to tcc have never been found in the present analyses. pogonophora and "basal canalipalpata" in the present analyses, the pogonophora is closely related to the "clitellatomorpha" or, in absence of the latter group, pogonophora alone groups as a sister group of ssc. three groups of the traditional canalipalpata, namely, oweniidae, magelona, and chaetopteridae, were usually placed among the most basal annelids, or even outside the annelida, in the present all-species analyses. the taxon-exclusion analyses suggested that magelonids and oweniids might in fact be attracted strongly towards the remote annelid outgroups. in absence of all other "problematic" annelids, oweniidae alone grouped consistently with the pogonophora, and magelona either with the paraonidae or as a sister group of the cirratuliformia-ssc superclade. on the contrary, basal placement of the chaetopteridae cannot be excluded. amphinomida and aberranta in the most present analyses, aberranta is a sister group of the amphinomida, and the whole clade is one of the basalmost annelid branches, far from the other aciculata. however, in the taxon-exclusion tests, the aberranta-amphinomida clade is placed as a sister group of the phyllodocida or even within it. it is then possible that the aberranta-amphinomida clade is, in fact, one of subgroups of the monophyletic aciculata, misplaced in most molecular trees. therefore, it seems rather premature to regard amphinomida as a basal group, "based on the tetraneurous organization of the nervous system"; moreover, the presence of several peripheral longitudinal nerves is not limited to the amphinomids. "core archiannelids" monophyly of the "archiannelida" has been rejected by all modern authors, whereas the monophyly of protodrilida as well as its spionidan affinities has been proposed recently. the polygordiids were regarded as relatives of protodrilidans or of opheliids, or as the canalipalpatans of uncertain position. surprisingly, the molecular trees tend to include a clade covering most of the traditional "archiannelids". in the present all-taxa bi tree, there is a well-supported basal annelid clade including nerillidae-protodrilidae and polygordiidae-saccocirridae. although nerillidae were considered aciculatans of uncertain position, closer relationships of the nerillidae with any aciculata have never been retrieved in the present analyses. in conclusion, it is an interesting working hypothesis that the "archiannelida" might form a clade, either basal, or close to the ssc. sipunculida and dinophilidae the sipunculida have been considered a separate phylum by most authors. although they as adults do not exhibit any signs of segmentation, sipunculids show transitional stages of segmentation during development of their ventral nerve cord. analyses of the mitochondrial genomes as well as phylogenomics suggest that the sipunculids are an annelid ingroup. the unique correspondence of podocyte lining the metanephridia appears to join sipunculida with the sabellida and terebelliformia. the pharyngeal apparatus in the sipunculid pelagosphere larvae is similar to that found in the cirratuliformia. in the present trees, the sipunculids have always been found as an annelid ingroup, often close to the dinophilidae. no closer relationships between sipunculids and terebelliformians, sabellidans, oweniids or chaetopterids were recovered here. the enigmatic dinophilidae were never found to be closely related to the dorvilleidae, i.e. in the placement expected by the morphologists. even parapodrilus, one of the presumably dinophilid-related, "progenetic" dorvilleids, groups consistently with other dorvilleids within the eunicida and shows no affinities to the dinophilidae. in the taxon-exclusion analyses, both dinophilidae and sipunculida group within the cirratuliformia, or they are a sister group of the pogonophora-"clitellatomorpha" superclade. in conclusion, close affinities between dinophilidae and sipunculida appear as a possible working hypothesis, but the precise position of this clade remains uncertain. myzostomida relationships of the myzostomida, traditionally regarded as aberrant polychaetes, probably phyllodocidans, are uncertain. they may be either basal protostomes or platyzoan relatives. their highly aberrant sequences and uncertain homology of many morphological characters do not allow to deduce their relationships precisely. nevertheless, the numerous annelid-like traits of the myzostomida still could corroborate some polychaete-myzostomid proximity. recently, bleidorn et al. re-examined this issue by analysis of four nuclear genes and a mitochondrial genome and showed myzostomids are likely part of the annelid radiation. on the contrary, in the comprehensive phylogenomic analysis of the metazoa, myzostomida are placed within the platyzoa. in the present analyses, the myzostomids seem to belong into the annelida. however, the taxon sampling in this paper does not provide a suitable test for alternative hypotheses due to lack of most of the possible non-annelid relatives of the myzostomida.  the combined phylogenetic analysis provides a modified view of annelid evolution. several higher-level annelid taxa are suggested by our analyses, i.e. phyllodocida, eunicida, the orbinioid-parergodrilid clade, cirratuliformia, sabelloid-spionoid clade, terebelloid-capitellid clade, and "clitellatomorpha". although the deep-level evolutionary relationships of annelida remain poorly understood, we propose sister-group relationships between the phyllodocida-aberranta-amphinomida and eunicida-opc clades, between the cirratuliformia and ssc, and possibly also between the "clitellatomorpha" and oweniidae-pogonophora clades. two unorthodox clades, "core archiannelida" and dinophilidae-sipunculida, are proposed here. 
the combined phylogenetic analysis provides a modified view of annelid evolution, with several higher-level taxa, i.e. the position of the remaining annelid groups is uncertain – the most problematic taxa are the opheliidae-scalibregmatidae clade, the amphinomida-aberranta clade, apistobranchus, chaetopteridae, myzostomida, the sipunculida-dinophilidae clade, and the "core archiannelida". two unorthodox clades, the "core archiannelida" and sipunculida-dinophilidae, are proposed. the analysis of the combined dataset yields the following scheme of relationships: phyllodocida and eunicida are monophyletic groups, together probably forming monophyletic aciculata. the clitellata and "clitellate-like polychaetes" form a monophyletic group. phyllodocida, eunicida, orbinioid-parergodrilid clade, cirratuliformia, sabelloid-spionoid clade, terebelloid-capitelloid clade, and "clitellatomorpha". although the deep-level evolutionary relationships of annelida remain poorly understood, we propose the monophyly of the aciculata, sister-group relationships between the eunicida and opc, between the cirratuliformia and ssc, and possibly also between the "clitellatomorpha" and oweniidae-pogonophora clades. the traditional "scolecida" and "canalipalpata" are both polyphyletic, forming instead two clades: one including cirratuliformia and the "sabelloid-spionoid clade", the other including terebelliformia, arenicolidae-maldanidae, and capitellidae-echiurida. no attempt has yet been made to analyse simultaneously morphological and molecular information concerning the annelida as a whole. sthe "total-evidence" analyses combining morphological and molecular characters have been published for a few annelid taxa.
 annelida is one of the major protostome phyla, whose deep phylogeny is very poorly understood. recent molecular phylogenies show that annelida may include groups once considered separate phyla and that clitellata are derived polychaetes. sthe "total-evidence" analyses combining morphological and molecular characters have been published for a few annelid taxa. no attempt has yet been made to analyse simultaneously morphological and molecular information concerning the annelida as a whole.  phylogenetic relationships within annelida were analysed on the basis of morphological characters and sequences of six genes, altogether, terminals of all annelid "families" and informative characters, by bayesian and maximum-parsimony methods. the analysis of the combined dataset yields the following scheme of relationships: phyllodocida and eunicida are monophyletic groups, together probably forming monophyletic aciculata. the traditional "scolecida" and "canalipalpata" are both polyphyletic, forming instead two clades: one including cirratuliformia and the "sabelloid-spionoid clade", the other including terebelliformia, arenicolidae-maldanidae, and capitellidae-echiurida. the clitellata and "clitellate-like polychaetes" form a monophyletic group. the position of the remaining annelid groups is uncertain – the most problematic taxa are the opheliidae-scalibregmatidae clade, the amphinomida-aberranta clade, apistobranchus, chaetopteridae, myzostomida, the sipunculida-dinophilidae clade, and the "core archiannelida".  the combined phylogenetic analysis provides a modified view of annelid evolution, with several higher-level taxa, i.e. phyllodocida, eunicida, orbinioid-parergodrilid clade, cirratuliformia, sabelloid-spionoid clade, terebelloid-capitelloid clade, and "clitellatomorpha". two unorthodox clades, the "core archiannelida" and sipunculida-dinophilidae, are proposed. although the deep-level evolutionary relationships of annelida remain poorly understood, we propose the monophyly of the aciculata, sister-group relationships between the eunicida and opc, between the cirratuliformia and ssc, and possibly also between the "clitellatomorpha" and oweniidae-pogonophora clades. 