Evidence for a cordal, not ganglionic, pattern of cephalopod brain neurogenesis

DWhatley

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Evidence for a cordal, not ganglionic, pattern of cephalopod brain neurogenesis
Shuichi Shigeno, Rahul Parnaik, Caroline B. Albertin, Clifton W. Ragsdale 2015 (full paper)

Contains several excellent image collages of developing bimacs (DWhatley)

Our study of neurogenetic gene expression in octopus embryo wholemounts indicates that the anlagen of the octopus brain follow a multi-cordal plan rather than one of multiple spherical ganglia such as those seen in the adult nervous system architecture of gastropod species, such as Aplysia,Lymnaea, and Helix48]. This finding, together with the cord-like organization postulated recently for Nautilus embryos 34], strongly suggests that a multiple cord origin for the cephalopod brain is a shared feature of extant cephalopods. Recent molecular phylogenetic studies establish a close relationship between cephalopods and monoplacophorans 29], 49], 50] and ratify fossil evidence that cephalopods evolved from a monoplacophoran-like mollusc 6], 51]. The cord-like organization of the embryonic cephalopod nervous system can therefore be directly compared with the cerebral, palliovisceral (or pleurovisceral) and pedal medullary cords described in embryonic and adult monoplacophoran and polyplacophoran nervous systems 52]–59]. One compelling interpretation of these data is that cephalopods, despite the large size and compact organization of their brains, have retained an ancestral molluscan nervous system plan of multiple neural cords55], 57], 59], and that this plan is particularly conspicuous in the embryo.
 

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