Fig. 1
Sketch drawing modified from Wollesen et al. [44]
The presence and absence of cerebral eyes in adult recent mollusks. The last common cephalopod and gastropod ancestors possessed probably a pair of adult cerebral eyes (+), while the ancestors of all other molluscan clades most likely did not exhibit cerebral eyes (−). Adult polyplacophorans possess a sensory system with lenses in the tegmental layer of the shell valves, so-called esthetes. Certain bivalves evolved eyes associated with their mantle tissue. Phylogenetic analysis based on Smith et al. [28]