A survey of the morphology of the brains (cerebral ganglia) of 13 species of decapods shows that all have common areas of neuropil that are developed to differing degrees in the different groups. The neuropils of the paired accessory lobes, however, appear to have evolved de novo in the Reptantia. Phylogenetic relationships within the Reptantia suggest that the accessory lobes were initially large but became reduced in size during the evolution of the brachyurans and anomalans.
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Sandeman et al. (1993) studied this question.
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