Connectome of a syncytial nerve net

Connectomics 2026 – Berlin Harnack House – 28 June - 1 July 2026

Gáspár Jékely

Centre for Organismal Studies, Heidelberg University

@jekely@biologists.social

Ciliated zooplankton larvae

The non-bilaterian Metazoa

Ctenophores

Ernst Haeckel, Kunstformen der Natur (1904), plate 27: Ctenophorae

Bolinopsis

  • Irideszenz (von iris = Regenbogen, griech.)

Eukaryotic cilia

Emelie Brodrick


Lin et al, 2018

Ctenophora - Comb plates

  • comb plates of thousands of cilia
  • glued together by “compartmenting lamellae”
  • cilia beat together as a plate - breaking low-Reynolds barrier

Ctenophora - Comb plates

Comb plates

The ctenophore nervous system is syncytial

  • one large syncytial nerve-net
  • covers the entire body wall

Ctenophores – biradial symmetry

Pleurobrachia



  • biradial symmetry
  • two orthogonal planes: tentacular and sagittal

Balancer organ

  • balancer organ = statocyst in the aboral organ
  • stone cells = statolyths are balanced on four bundles of cilia
  • change in orientation -> differential load on balancer cilia -> frequency change
  • balancer beat-frequency propagates to comb rows

Balancer cilia respond to statocyst load



vEM of the ctenophore gravisensory organ

Kei Jokura

Ciliary bundles of the balancer supporting the statolyth

An aboral nerve net underneath the balancers

Two small and one large nerve net



  • balancers       SSN_Q12   SSN_Q34      SSN_Q1-4                  

Connectome of the ctenophore balancer



  • three syncytial nerve-net neurons
  • nerve-net synapses on balancer cells
  • no synapses from balancer to nerve net
  • nerve nets synapse on each other
  • not an input-output organisation
  • nerve net coordinates the sensory-motor balancers

High-speed imaging of balancer cilia

  • regular arrests of ciliary beating

Synchronisation of balancer cilia

Connectome of the ctenophore balancer

  • global coordination of balancer cells
  • synchronisation of arrests (2x2 bundles)
  • synchronisation of re-beat (all 4 bundles)

Acknowledgements

  • Alexandra Kerbl
  • Karel Mocaer
  • Sanja Jasek
  • David Hug
  • Jules Duruz
  • Mateusz Kostecki
  • Benedikt Dürr
  • Kata Szabó
  • Emily Savage
  • Simone Wolters
  • Anja Ciprianidis
  • Kevin Urbansky

Alumni

  • Kei Jokura (NIBB, Okazaki)
  • Luis Bezares (LBDV, Villefranche-sur-mer)
  • Luis Yanez-Guerra (Uni Sussex)
  • Emelie Brodrick (Sussex)
  • Csaba Verasztó (EPFL)

Facilities

  • Réza Shahidi
  • Charlotta Funaya
  • Ulrike Engel