| Keyword | | | Author keywords | Spiralia, ring-shaped brain, lateral medullary cords, nervous system development, larval nervous system |
| Authors | | Top | - Beckers, P.
- von Döhren, J.
| | |
| Abstract | Nemertea is a spiralian phylum comprising approximately 1300 species of mostly marine, nocturnal predators. Prey is captured with an eversible proboscis housed in a dorsally located fluid filled secondary body cavity, called rhynchocoel. Three major clades are recognized: Hoplonemertea, Pilidiophora, and Palaeonemertea. The main components of the nemertean nervous system are a ring-shaped brain around the rhynchocoel, and paired lateral, longitudinal medullary cords that are confluent with the ventral brain lobes. Additional, variable components of the nervous system are longitudinal cephalic, oesophageal, and proboscis nerves and various plexuses. Sensory organs comprise eyes, cerebral organs, frontal organs, and various epidermal sensory structures. Most of the canonic spiralian neurotransmitters have been detected, with FMRFamide-like neuropeptides being the most prevalent. Larvae of palaeo- and hoplonemertean species show virtually no transitory nervous elements, while the pilidium-larva of Pilidiophora possesses an extensive transitory larval nervous system. Among the first definite neural elements to develop in all species is the brain ring, followed by the lateral medullary cords. Data on neural development and morphology of other spiralian clades, as well as molecular data, support the scenario that a frontal brain with paired lateral medullary cords as present in Nemertea represents the ancestral spiralian nervous system architecture. |
|
