AUTHOR=Kalke Paul , Linder Samira S. , Beckers Patrick , Helm Conrad 

TITLE=Palps across the tree – the neuronal innervation and development of sensory head appendages in Annelida

JOURNAL=Frontiers in Neuroscience

VOLUME=Volume 17 - 2023

YEAR=2024

URL=https://www.frontiersin.org/journals/neuroscience/articles/10.3389/fnins.2023.1310225

DOI=10.3389/fnins.2023.1310225

ISSN=1662-453X

ABSTRACT=Polychaetes inhabit a hugewide variety of habitats and hence show an even greatera great morphological diversity. In this context, a key morphological structure to adaptfor adapting to their individual lifestyles and ecological niches are the prominent head appendages.In the last years more and more studies focussed on the mainly sensory annelid head appendagesnamely the antennae, palps, buccal lips and cirri -to unravel the evolutionary origin and phylogeny of Annelida. Unfortunately, comparable data for most of the polychaete families are lacking so far, especially when it comes to features of the larval anterior nervous system and the related innervation and potential homology of these head appendages. In this study, we therefore use an integrative morphological approach including immunohistochemistry and confocal laser scanning microscopy in combination with histological serial sections and 3D-visualisation.visualisations. With special focus on the palps, this comprehensive dataset is used to providepalp-like appendages, our data provides a closer look into the development of the larval anterior nervous system and the related sensory systemstructures of three polychaete families representing major groups of the annelid tree of life. Hence, we investigate members of the palaeoannelid Magelonidae -as member of the Paleoannelida -as well as basally-branching Amphinomidae as representing the sister group of Errantia, and Sedentaria (Pleistoannelida), and the derivedthe pleistoannelid Spionidae forming a taxon deeply nested within the latterSedentaria. Our detailedcomparative data of larval and adult neuronal features and scaffolds support the homology of feeding palps across the annelid tree. Furthermore, our observations show that larval palps gradually transform into the adult ones while keeping a very similar neuronal innervation pattern. Solely for Amphinomidae a loss of larval palps during ontogenesis has to be assumed. Therefore, our investigations enlightuncover important and so far unknown details in terms of structural homology across Annelida and areprovide important results necessary for our understanding of annelid evolution.