DOI: 10.5061/dryad.m8k24
title: Data from: Owenia fusiformis - a basally branching annelid suitable for studying ancestral features of annelid neural development

description: Background-Comparative investigations on bilaterian neurogenesis shed
 light on conserved developmental mechanisms across taxa. With respect to
 annelids, most studies focus on taxa deeply nested within the annelid
 tree, while investigations on early branching groups are almost lacking.
 According to recent phylogenomic data on annelid evolution Oweniidae
 represent one of the basally branching annelid clades. Oweniids are
 thought to exhibit several plesiomorphic characters, but are scarcely
 studied - a fact that might be caused by the unique morphology and unusual
 metamorphosis of the mitraria larva, which seems to be hardly comparable
 to other annelid larva. In our study, we compare the development of
 oweniid neuroarchitecture with that of other annelids aimed to figure out
 whether oweniids may represent suitable study subjects to unravel
 ancestral patterns of annelid neural development. Our study provides the
 first data on nervous system development in basally branching annelids.
 Results-Based on histology, electron microscopy and immunohistochemical
 investigations we show that development and metamorphosis of the mitraria
 larva has many parallels to other annelids irrespective of the drastic
 changes in body shape during metamorphosis. Such significant changes
 ensuing metamorphosis are mainly from diminution of a huge larval
 blastocoel and not from major restructuring of body organization. The
 larval nervous system features a prominent apical organ formed by
 flask-shaped perikarya and circumesophageal connectives that interconnect
 the apical and trunk nervous systems, in addition to serially arranged
 clusters of perikarya showing 5-HT-LIR in the ventral nerve cord, and
 lateral nerves. Both 5-HT-LIR and FMRFamide-LIR are present in a distinct
 nerve ring underlying the equatorial ciliary band. The connections arising
 from these cells innervate the circumesophageal connectives as well as the
 larval brain via dorsal and ventral neurites. Notably, no distinct somata
 with 5-HT -LIR in the apical organ are detectable in the larval stages of
 Owenia. Most of the larval neural elements including parts of the apical
 organ are preserved during metamorphosis and contribute to the juvenile
 nervous system. Conclusions-Our studies in Owenia fusiformis strongly
 support that early branching annelids are comparable to other annelids
 with regard to larval neuroanatomy and formation of the juvenile nervous
 system. Therefore, Owenia fusiformis turns out to be a valuable study
 subject for comparative investigations and unravelling ancestral processes
 in neural development in Annelida and Bilateria in general.
description: Additional file
 1_1dpf_FMRF_aTub_DAPI_lateralConfocal z-stack showing
 FMRFamide-LIR (purple), aTub-LIR (cyan) and DAPI staining (dark blue) of
 the 1 dpf stage. Lateral view. Note that the staining of peripheral nerves
 is scarce.Additional file
 2_7dpf_5HT_aTub_DAPI_apical viewConfocal z-stack showing
 5-HT-LIR (purple), aTub-LIR (cyan) and DAPI staining (dark blue) of the 7
 dpf stage. Apical view. Note that the staining of peripheral nerves is
 scarce.Additional file
 3_7dpf_FMRF_aTub_DAPI_apical organConfocal z-stack showing
 FMRFamide-LIR (purple), aTub-LIR (cyan) and DAPI staining (dark blue) of
 the 7 dpf stage. Apical view of the apical organ.Additional file
 4_14dpf_aTub_DAPI_lateralConfocal z-stack showing
 aTub-LIR (cyan) and DAPI staining (dark blue) of the 14 dpf stage. Lateral
 view.Additional file
 5_14dpf_FMRF_aTub_DAPI_apicalConfocal z-stack showing
 FMRFamide-LIR (purple), aTub-LIR (cyan) and DAPI staining (dark blue) of
 the 14 dpf stage. Apical view. Note that the staining of peripheral nerves
 is scarce.Additional file
 6_14dpf_FMRF_aTub_DAPI_lateralConfocal z-stack showing
 FMRFamide-LIR (purple), aTub-LIR (cyan) and DAPI staining (dark blue) of
 the 14 dpf stage. Lateral view. Note that the staining of peripheral
 nerves is scarce.Additional file
 7_14dpf_5HT_aTub_DAPI_lateralConfocal z-stack showing
 5-HT-LIR (purple), aTub-LIR (cyan) and DAPI staining (dark blue) of the 14
 dpf stage. Lateral view. Note that the staining of peripheral nerves is
 scarce.