Fig. 7
From: Nervous system development in the Pacific oyster, Crassostrea gigas (Mollusca: Bivalvia)
Phylogenic tree of major bivalve lineages based on González et al. [1], revealing ground patterns based on morphological data of neurogenesis of bivalves that have been investigated. Pink cells are 5-HT-ir cells of the AO in the studied species. Ventral nerve cord (VNC, black parallel lines) with red ganglia (top is the cerebral, middle is the pedal, and bottom is the ventral ganglion). Protobranchia (non-published data), Pteriomorpha, and Imparidentia show three flask-shaped cells in the AO. Within Pteriomorpha mussels and oysters possess a VNC with three paired ganglia, while Protobranchia and Imparidentia have a VNC with only a cerebral ganglion