Organisms Diversity & Evolution

, Volume 17, Issue 2, pp 447–475 | Cite as

Morphology and evolution of the nervous system in Gnathostomulida (Gnathifera, Spiralia)

  • Ludwik Gąsiorowski
  • Nicolas Bekkouche
  • Katrine WorsaaeEmail author
Original Article


Within Spiralia, Gnathifera may represent the deepest branching lineage comprising the jaw worms Gnathostomulida and their sister group Micrognathozoa + Syndermata. Yet, very few nervous system studies have been conducted on this lineage of microscopic, jaw-bearing worms, limiting our understanding of the evolution of this organ system in Spiralia. The nervous system of representatives from all major groups of Gnathostomulida was here mapped using confocal laser scanning microscopy and immunohistochemistry. Their intra-epidermal, unsegmented nervous systems comprise an anterior brain and three to five ventral and two to four dorsal longitudinal nerves, connected by few transverse commissures. Neurites of the stomatogastric nervous system were found lining the pharynx and connecting to a prominent buccal ganglion. Supposedly, sensory ciliated cells in the pharynx and the gut were documented for the first time. Based on these morphological results, primary homologies of neural structures in Gnathostomulida and other Gnathifera were hypothesized and thereafter tested using parsimony. This first neurophylogeny of Gnathostomulida resulted in a topology congruent with molecular data, supporting the monophyly of Bursovaginoidea, Conophoralia, and Scleroperalia. From this topology, the evolution of the gnathostomulid nervous system was reconstructed. It suggests a specialization and diversification of cords and serotonin-like immunoreactive cell patterns from a plesiomorphic neuroarchitecture of three unsegmented nerve cords and a compact anterior brain and buccal ganglion. These plesiomorphic states resemble the nervous system of Micrognathozoa, and possibly the ancestral states of Spiralia.


Neurobiology Meiofauna Lophotrochozoa Neurotransmitters Phylogeny 



We are very grateful to Wolfgang Sterrer, who helped with taxonomical identification of examined Gnathostomulida. We are also indebted to M.V. Sørensen, R. M. Kristensen, and A. Schmidt-Rhaesa, who shared information on good sampling sites for Gnathostomulida; R. M. Kristensen additionally aided with helpful comments on sensory structures and discussions of his unpublished material. We wish to thank as well all our colleagues, who helped with sampling and collecting of the material (especially A. Kerbl, B. Gonzalez and A. Martínez). This study was supported by the Villum Foundation (grant no. 102544).

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

Supplementary material

13127_2017_324_MOESM1_ESM.pdf (157 kb)
ESM 1 (PDF 156 kb)
13127_2017_324_MOESM2_ESM.pdf (935 kb)
ESM 2 (PDF 935 kb)


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© Gesellschaft für Biologische Systematik 2017

Authors and Affiliations

  1. 1.Marine Biological Section, Department of BiologyUniversity of CopenhagenCopenhagen ØDenmark

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