May the palps be with you – new insights into the evolutionary origin of anterior appendages in Terebelliformia (Annelida)

Abstract Background Head appendages in Annelida contribute significantly to the immense morphological diversity in this spiralian taxon. Nevertheless, the evolutionary origin of annelid antennae, palps, cirri and tentacles are part of vast theories and debates that took place over decades. One of th...

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Autores principales:	Paul Kalke, Patrick Beckers, Conrad Helm
Formato:	article
Lenguaje:	EN
Publicado:	BMC 2021
Materias:	Segmented worms Morphology Nervous system Tentacles Comparative approach Histology Zoology QL1-991
Acceso en línea:	https://doaj.org/article/77a45af550ae42628e420de2670ea5a6
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spelling	oai:doaj.org-article:77a45af550ae42628e420de2670ea5a62021-11-21T12:08:14ZMay the palps be with you – new insights into the evolutionary origin of anterior appendages in Terebelliformia (Annelida)10.1186/s40850-021-00094-62056-3132https://doaj.org/article/77a45af550ae42628e420de2670ea5a62021-11-01T00:00:00Zhttps://doi.org/10.1186/s40850-021-00094-6https://doaj.org/toc/2056-3132Abstract Background Head appendages in Annelida contribute significantly to the immense morphological diversity in this spiralian taxon. Nevertheless, the evolutionary origin of annelid antennae, palps, cirri and tentacles are part of vast theories and debates that took place over decades. One of these heavily discussed groups are the Terebelliformia, which bear numerous anterior tentacles originating from different regions of the head. The question, whether these tentacles are homologous to feeding palps in other annelids or if these structures evolved convergently in terebellids and the remaining taxa, has been highly debated in the past. Results By using morphological methods including immunohistochemistry, confocal microscopy, Azan-stained serial sections and 3D-visualisation, we are able to shed new light and a fresh look on the old question of the evolutionary origin of the buccal tentacles and their associated head structures in Terebelliformia. Our investigations show that the brains of the ampharetid Hypania invalida and the aulophora larvae of Lanice conchilega (Terebellidae) consist of a dorsal, more prominent and a more slender, ventral brain region. Neurite bundles innervating the buccal tentacles split off from the ventral and dorsal root within the ventral brain region and thus originate from the dorsal and ventral root of the circumoesophageal connectives. Hence, the observed neurite bundles fulfil the morphological criteria for the innervating neurite bundles of feeding palps known from Paleoannelida. Conclusions We disagree with former conclusions that buccal tentacles are part of the alimentary canal. Based on the presented data, the buccal tentacles of terebelliform taxa are innervated by neurite bundles and can be homologized with peristomial feeding palps of other Annelida. Our comparative investigations reveal important insights into morphological changes during the evolution of anterior head appendages in Terebelliformia and Annelida in general. Nevertheless, our analyses also illustrate the gaps in knowledge and that more investigations throughout the annelid tree are necessary to explain and understand the huge diversity of annelid anterior appendages.Paul KalkePatrick BeckersConrad HelmBMCarticleSegmented wormsMorphologyNervous systemTentaclesComparative approachHistologyZoologyQL1-991ENBMC Zoology, Vol 6, Iss 1, Pp 1-14 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	Segmented worms Morphology Nervous system Tentacles Comparative approach Histology Zoology QL1-991
spellingShingle	Segmented worms Morphology Nervous system Tentacles Comparative approach Histology Zoology QL1-991 Paul Kalke Patrick Beckers Conrad Helm May the palps be with you – new insights into the evolutionary origin of anterior appendages in Terebelliformia (Annelida)
description	Abstract Background Head appendages in Annelida contribute significantly to the immense morphological diversity in this spiralian taxon. Nevertheless, the evolutionary origin of annelid antennae, palps, cirri and tentacles are part of vast theories and debates that took place over decades. One of these heavily discussed groups are the Terebelliformia, which bear numerous anterior tentacles originating from different regions of the head. The question, whether these tentacles are homologous to feeding palps in other annelids or if these structures evolved convergently in terebellids and the remaining taxa, has been highly debated in the past. Results By using morphological methods including immunohistochemistry, confocal microscopy, Azan-stained serial sections and 3D-visualisation, we are able to shed new light and a fresh look on the old question of the evolutionary origin of the buccal tentacles and their associated head structures in Terebelliformia. Our investigations show that the brains of the ampharetid Hypania invalida and the aulophora larvae of Lanice conchilega (Terebellidae) consist of a dorsal, more prominent and a more slender, ventral brain region. Neurite bundles innervating the buccal tentacles split off from the ventral and dorsal root within the ventral brain region and thus originate from the dorsal and ventral root of the circumoesophageal connectives. Hence, the observed neurite bundles fulfil the morphological criteria for the innervating neurite bundles of feeding palps known from Paleoannelida. Conclusions We disagree with former conclusions that buccal tentacles are part of the alimentary canal. Based on the presented data, the buccal tentacles of terebelliform taxa are innervated by neurite bundles and can be homologized with peristomial feeding palps of other Annelida. Our comparative investigations reveal important insights into morphological changes during the evolution of anterior head appendages in Terebelliformia and Annelida in general. Nevertheless, our analyses also illustrate the gaps in knowledge and that more investigations throughout the annelid tree are necessary to explain and understand the huge diversity of annelid anterior appendages.
format	article
author	Paul Kalke Patrick Beckers Conrad Helm
author_facet	Paul Kalke Patrick Beckers Conrad Helm
author_sort	Paul Kalke
title	May the palps be with you – new insights into the evolutionary origin of anterior appendages in Terebelliformia (Annelida)
title_short	May the palps be with you – new insights into the evolutionary origin of anterior appendages in Terebelliformia (Annelida)
title_full	May the palps be with you – new insights into the evolutionary origin of anterior appendages in Terebelliformia (Annelida)
title_fullStr	May the palps be with you – new insights into the evolutionary origin of anterior appendages in Terebelliformia (Annelida)
title_full_unstemmed	May the palps be with you – new insights into the evolutionary origin of anterior appendages in Terebelliformia (Annelida)
title_sort	may the palps be with you – new insights into the evolutionary origin of anterior appendages in terebelliformia (annelida)
publisher	BMC
publishDate	2021
url	https://doaj.org/article/77a45af550ae42628e420de2670ea5a6
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May the palps be with you – new insights into the evolutionary origin of anterior appendages in Terebelliformia (Annelida)

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