The protocerebrum and its sensory organs in maxillopodan crustaceans: testing the basal phylogenetic relationships within Tetraconata/Pancrustacea

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The protocerebrum is the anteriormost part of the crustacean brain. It receives input from major sensory organs such as the nauplius eye and compound eyes as well as from the enigmatic frontal filament organs. The evolutionary origin of the protocerebrum, in crustaceans and arthropods in general, is under debate and the focus of ongoing research. Regrettably, only very few details are known from maxillopodan crustaceans such as fish lice (Branchiura), barnacles (Cirripedia), copepods, ostracodes and interstitial mystacocarids. These groups, however, play a crucial role in understanding the evolution of Tetraconata/Pancrustacea. Our project will provide new data on the protocerebrum and its sensory organs in various maxillopodans using state of the art techniques such as immunohistochemistry, volume electron microscopy and x-ray microcomputer tomography. The goal of the proposed project is to understand the neuroarchitecture of the protocerebrum and the protocerebral sense organs and to contribute morphological characters which will lead to a better understanding of the evolutionary morphology (sensu Richter & Wirkner 2014) of maxillopodan crustaceans and crustaceans in general. We will investigate (1) which components of a protocerebral central complex are present in the various maxillopodan taxa, (2) the neuroarchitecture of the two optic lobes, testing their homology to those in branchiopods and other Tetraconata, (3) the ultrastructure of the compound eyes, testing the presence of primary pigment cells outside hexapods, (4) the ultrastructure of the nauplius eye, testing the homology status of the tapetum layer, and (5) the innervation and ultrastructure of the enigmatic frontal filament organs, providing evidence or counter-evidence for their homology throughout crustaceans.