The nervous systems of Pilidiophora (Nemertea)


Today molecular data recover three higher taxa in nemerteans, Palaeonemertea, Pilidiophora and Hoplonemertea. Hubrechtella dubia, a former palaeonemertean taxon was excluded from palaeonemerteans and is now supported as the sister group to heteronemerteans. This taxon is called Pilidiophora, because H. dubia and Heteronemertea share a pilidium larva. To find additional morphological evidence for Pilidiophora, the nervous system of 13 species of this taxon were investigated using different histological techniques. The central or medullated nervous system of nemerteans consists of a ring-shaped brain and lateral branching medullary cords. While the brain of basally branching nemerteans shows no or only slightly posterior enlargement, the brain of Pilidiophora expands caudally. Pilidiophora possess a conspicuous sensory organ, the cerebral organ. Although this organ is also found in hoplonemerteans and certain palaeonemertean species, only in Pilidiophora this organ is directly connected to the dorsal lobe of the brain. Additionally, this organ terminates in a layer of neurons close to the blood vessel in all pilidiophoran species. The analysis indicates that although in H. dubia some characters of the nervous system show the plesiomorphic state, the morphology of the cerebral organ provides an apomorphic character for a taxon Pilidiophora.

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The author thanks two anonymous reviewers who helped to improve the manuscript. The author thanks Malin Strand for collecting Hubrechtella dubia, Daria Krämer for collecting Cerebratulus fuscus and Notospermus geniculatus. Alexej Chernyshev gently provided specimen of Baseodiscus hemprichii. Christiane Wallnisch for technical support and Thomas Bartolomaeus for discussions and suggestions on the manuscript.

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Correspondence to Patrick Beckers.

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Communicated by Andreas Schmidt-Rhaesa.

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Beckers, P. The nervous systems of Pilidiophora (Nemertea). Zoomorphology 134, 1–24 (2015).

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  • Lophotrochozoa
  • Spiralia
  • Neuroanatomy
  • Heteronemertea
  • Pilidiophora
  • Hubrechtella dubia
  • 3D reconstruction