A New Look at the Ventral Nerve Centre of Sagitta: Implications for the Phylogenetic Position of Chaetognatha (arrow Worms) and the Evolution of the Bilaterian Nervous System

Overview

Journal Front Zool

Publisher Biomed Central

Specialty Biology

Date 2007 May 22

PMID 17511857

Citations 14

Authors

Steffen Harzsch

Carsten H G Muller

Affiliations

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Abstract

Background: The Chaetognatha (arrow worms) are a group of marine carnivores whose phylogenetic relationships are still vigorously debated. Molecular studies have as yet failed to come up with a stable hypothesis on their phylogenetic position. In a wide range of metazoans, the nervous system has proven to provide a wealth of characters for analysing phylogenetic relationships (neurophylogeny). Therefore, in the present study we explored the structure of the ventral nerve centre ("ventral ganglion") in Sagitta setosa with a set of histochemical and immunohistochemical markers.

Results: In specimens that were immunolabeled for acetylated-alpha tubulin the ventral nerve centre appeared to be a condensed continuation of the peripheral intraepidermal nerve plexus. Yet, synapsin immunolocalization showed that the ventral nerve centre is organized into a highly ordered array of ca. 80 serially arranged microcompartments. Immunohistochemistry against RFamide revealed a set of serially arranged individually identifiable neurons in the ventral nerve centre that we charted in detail.

Conclusion: The new information on the structure of the chaetognath nervous system is compared to previous descriptions of the ventral nerve centre which are critically evaluated. Our findings are discussed with regard to the debate on nervous system organisation in the last common bilaterian ancestor and with regard to the phylogenetic affinities of this Chaetognatha. We suggest to place the Chaetognatha within the Protostomia and argue against hypotheses which propose a deuterostome affinity of Chaetognatha or a sister-group relationship to all other Bilateria.

Citing Articles

Unfolding the ventral nerve center of chaetognaths.

Ordonez J, Wollesen T Neural Dev. 2024; 19(1):5.

PMID: 38720353 PMC: 11078758. DOI: 10.1186/s13064-024-00182-6.

A giant stem-group chaetognath.

Park T, Nielsen M, Parry L, Sorensen M, Lee M, Kihm J Sci Adv. 2024; 10(1):eadi6678.

PMID: 38170772 PMC: 10796117. DOI: 10.1126/sciadv.adi6678.

Neurons and Glia Cells in Marine Invertebrates: An Update.

Ortega A, Olivares-Banuelos T Front Neurosci. 2020; 14:121.

PMID: 32132895 PMC: 7040184. DOI: 10.3389/fnins.2020.00121.

Comparative analyses of olfactory systems in terrestrial crabs (Brachyura): evidence for aerial olfaction?.

Krieger J, Braun P, Rivera N, Schubart C, Muller C, Harzsch S PeerJ. 2015; 3:e1433.

PMID: 26713228 PMC: 4690415. DOI: 10.7717/peerj.1433.

Xenacoelomorpha: a case of independent nervous system centralization?.

Gavilan B, Perea-Atienza E, Martinez P Philos Trans R Soc Lond B Biol Sci. 2015; 371(1685):20150039.

PMID: 26598722 PMC: 4685578. DOI: 10.1098/rstb.2015.0039.

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