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Three-dimensional reconstruction of the central nervous system of Macrobiotus hufelandi (Eutardigrada, Parachela): implications for the phylogenetic position of Tardigrada


The morphology of the central nervous system of the tardigrade species Macrobiotus hufelandi was analysed with anti α-tubulin immunostaining in combination with confocal-laser-scanning-microscopy and computer aided three-dimensional reconstruction. The brain anatomy is unexpectedly complex with distinct tracts and highly intermingled nerve fibres. In contrast to older descriptions, we could not detect a suboesophageal ganglion. Furthermore, we found no evidence for a tripartite/three-segmented brain organisation. The median part of the brain is directly connected to the first pair of trunk ganglia via circumoesophageal connectives. Surprisingly, the four paired ventral ganglia do not show segmental commissures typical for the ladder-like nervous system of arthropods. Our findings constrain the phylogenetic position of Tardigrada. The much simpler organisation of the central nervous system of Tardigrada compared to that of Onychophora and Euarthropoda and some similarities to the nervous system of Cycloneuralia support a phylogenetic position of Tardigrada outside an Onychophora/Euarthropoda clade. This means that Tardigrada might be either the sister group to all other Arthropoda or they are more closely related to Cycloneuralia.

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We thank Greg Edgecombe for critical comments and the members of the group “Vergleichende Zoologie” at the Humboldt-Universität zu Berlin for many discussions and practical advices.

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Correspondence to Gerhard Scholtz.

Electronic supplementary material

The movies are interactive VR-QuickTime-movies and require a current version of QuickTime and JavaScript. By going with the mouse cursor into the movie frame and pressing the left mouse button you can move the 3-D-reconstruction in any position.

Movie 1: Ventral view of the entire body of Macrobiotus hufelandi (Hoechst, α-tubulin). Anterior is up. Visible are the arrangements of cell nuclei and fibre bundles in the head and the connection of the four ventral ganglia by the paired connectives (MOV 12.2 Mb)

Movie 2: Structure of the brain of Macrobiotus hufelandi (α-tubulin). In the starting position anterior is up, dorsal view. Visible are the dorsal commissure, preoral commissure, nerves n4 and n13, and the dorsal expansion of the dorsal clusters (MOV 14.5 Mb)

Movie 3: Nervous system in the head and the first ventral ganglion of Macrobiotus hufelandi (α-tubulin). Anterior is up, ventral view. The connectives of the chain of ventral ganglia run anteriorly representing the inner connectives which merge into the inner lobes of the brain. The outer connectives merge into the outer lobes (MOV 13.2 Mb)

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Zantke, J., Wolff, C. & Scholtz, G. Three-dimensional reconstruction of the central nervous system of Macrobiotus hufelandi (Eutardigrada, Parachela): implications for the phylogenetic position of Tardigrada. Zoomorphology 127, 21–36 (2008).

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  • Ventral Nerve Cord
  • Suboesophageal Ganglion
  • Ventral Ganglion
  • Segmental Ganglion
  • Outer Lobe