Reconstruction of the phylogeny of the five extant classes of the phylum Echinodermata has proven difficult. Results concerning higher-level taxonomic relationships among echinoderms are sensitive to the choice of analytical parameters and methods. Moreover, the proposal of a putative sixth class based on a small, enigmatic disc-shaped echinoderm, Xyloplax, from the deep seas of the Bahamas and New Zealand in the 1980s further complicated the problem. Although clearly an echinoderm, Xyloplax did not have clear affinity among known groups. Using molecular sequence and developmental data from recently collected Xyloplax adults and embryos we show that, rather than representing an ancient, distinct lineage as implied by its status as a class, Xyloplax is simply a starfish that is closely related to the asteroid family Pterasteridae. Many members of the Pterasteridae and all Xyloplax inhabit deep and polar seas and brood young. Brooding pterasterids and Xyloplax hold their young in specialized adult chambers until the young reach an advanced juvenile stage and are released as free-living individuals. We hypothesize that the unique morphology of Xyloplax evolved via progenesis - the truncation of somatic growth at a juvenile body plan but with gonadal growth to maturity. Although the overall phylogeny of extant echinoderms remains sensitive to choice of analytical methods, the placement of Xyloplax as sister to pterasterid asteroids is unequivocal. Based on this, we argue that the proposed class and infraclass status of Xyloplax should be suppressed.
18S.region1.may4.compress.fas
18S rDNA segment
18S.reg2.1.addpm2.compress
18S rDNA segment
18S.reg2.2.may4cos.compress
18S rDNA segment
28.0.may4.compress
28S rDNA segment
28.1.1.dec24.compress
28S rDNA segment
28.1.2.dec24.compress
28S rDNA segment
28S.3.1.dec24.compress
28S rDNA segment
28S.3.2.may4.compress
28S rDNA segment
28S.3.3.may4.compress
28S rDNA segment
28S.3.4.may4.compress
28S rDNA segment
28S.3.5.may4.compress
28S rDNA segment
28.4.jan2.compress
28S rDNA segment
S12.june16.compress
12S rDNA segment
trnar2.may4.compress.fixapril
DNA coding for mt tRNA segment
trnar3.may4.compress
DNA coding for mt tRNA segment
trnar4.may4.compress
DNA coding for mt tRNA segment
coi.may4.compress
DNA coding for cytochrome oxidase from mt
H3.june16.prealined
DNA coding for Histone H3
terminalsfile86
terminals file for poy analysis
accessionsfinal
Genbank accessions for DNA segments
pheno8636charafinal
annotated phenotype character matrix (tnt format)
primers
primers used in study
POY tree
19834.first.tre.zip
NEXUS file based on phenotypic data and implied alignment of molecular data
taxa86new.gapcost1tv2ts1.morph36charfinal.h3pre.first19834.nex.zip
MAP tree from MRBAYES search on implied alignment and phenotypic data
taxa86new.gapcost1tv2ts1.morph36charfinal.h3pre.first19834.best.tre.zip
CON tree from MRBAYES search on implied alignment and phenotypic data
note used dendroscope to view
taxa86new.gapcost1tv2ts1.morph36charfinal.h3pre.first19834.nex.con
taxa86new.h3prereally.16295.tre
NEXUS file based on implied alignment of molecuar data
taxa86new.h3prereally.diag16295exact.oneline.nex.zip
MAP tree from MRBAYES search on implied alignment
taxa86new.h3prereally.diag16295exact.mb.nex.map
CON tree from MRBAYES search on implied alignment and phenotypic data
note used dendroscope to view
taxa86new.h3prereally.diag16295exact.mb.nex.con
NEXUS file based on phenotypic data and clustalw alignment of molecular data
taxa8611005mb.morphfix.nex.zip
MAP tree from MRBAYES search on phenotypic data and clustalw alignment of molecular data
taxa8611005mb.morphfix.nex.map.zip
CON tree from MRBAYES search on phenotypic data and clustalw alignment of molecular data
note used dendroscope to view
taxa8611005mb.morphfix.nex.con
NEXUS file based on clustalw alignment of molecular data
taxa8611005mb.nex.zip
CON tree from MRBAYES search on clustalw alignment of molecular data
taxa8611005mb.nex.con
MAP tree from MRBAYES search on clustalw alignment of molecular data
taxa8611005mb.nex.map.zip