Homology and evolution of the chaetae in Echiura (Annelida)

PloS One
Ekin TilicThomas Bartolomaeus

Abstract

Echiura is traditionally regarded as a small phylum of unsegmented spiralian worms. Molecular analyses, however, provide unquestionable evidence that Echiura are derived annelids that lost segmentation. Like annelids, echiurans possess chaetae, a single ventral pair in all species and one or two additional caudal hemi-circles of chaetae in two subgroups, but their evolutionary origin and affiliation to annelid chaetae are unresolved. Since annelids possess segmental pairs of dorsal (notopodial) and ventral (neuropodial) chaetae that are arranged in a row, the ventral chaetae in Echiura either represent a single or a paired neuropodial group of chaetae, while the caudal circle may represent fused rows of chaetae. In annelids, chaetogenesis is generally restricted to the ventral part of the notopodial chaetal sac and to the dorsal part of the neuropodial chaetal sac. We used the exact position of the chaetal formation site in the echiuran species, Thalassema thalassemum (Pallas, 1766) and Echiurus echiurus (Pallas, 1767), to test different hypotheses of the evolution of echiurid chaetae. As in annelids, a single chaetoblast is responsible for chaetogenesis in both species. Each chaeta of the ventral pair arises from its own chaet...Continue Reading

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Citations

Apr 25, 2019·International Journal of Molecular Sciences·Xitan HouZhifeng Zhang
Nov 24, 2020·Zoology : Analysis of Complex Systems, ZACS·Petr KuznetsovElena Temereva
Dec 22, 2021·Biological Reviews of the Cambridge Philosophical Society·Guillermo Ponz-SegrellesM Teresa Aguado

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Datasets Mentioned

BETA
KM187648.1

Methods Mentioned

BETA
transmission electron microscopy
electron-microscopy
electron microscopy

Software Mentioned

IMOD
MorphDBase
align
3ds max

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