Meeting Abstract
Stomatopods have one of the most complex visual systems amongst all invertebrates. Specialised photoreceptors are arranged in 6 equatorial rows of ommatidia (the midband), dividing the eye in an upper and lower hemisphere. The 6 rows contain receptors detecting 12 spectral channels in addition to circularly polarised light. The hemispheres are achromatic, but detect linearly polarised light. How these information channels are processed remain elusive, although behavioural and neuroanatomical experiments suggest that they may use a processing system different from other animals. The shape and equal spread of the spectral sensitivities (from UV to far red) across investigated species combined with the fact that stomatopods use scanning eye movements also support such a hypothesis. While the stomatopod retina has been carefully examined, little is known about the neural architecture underlying the elaborate retina. Our studies resolve the neuronal pathway from the midband as segregated through the lamina and medulla before being integrated via lateral collaterals with hemispheral information in the lobula. Segregated relays from the lobula then project into the medulla terminals to numerous glomeruli, comparable to optic glomeruli found in insects. Stomatopods appear, however, to have a higher number of glomeruli than insects, even those with sophisticated visual behaviors. In addition, the stomatopod central complex (CX), receiving afferents from the medulla terminalis, also correspond in detail to the CX of insects. Either this is an extreme example of convergent evolution or it reveals genealogical correspondence of hexapod and eumalacostracan brains, implying the retention of complex ancestral brain organization in divergent pancrustacean lineages.
