COMPARATIVE ORGANIZATION OF OPTIC LOBES IN CRUSTACEANS: HEMIGRAPSUS NUDUS

Abstract

The common structure of optic neuropils connected by chiasmata has been used to propose that crustaceans and insects share a common ancestor. It was expected that comparisons of common organizations across taxa would reflect a sister group relationship between crustaceans and insects. However, recent studies revealed profound differences between the four synaptic regions across taxa, suggesting that the organization of neurons in these systems do not immediately reflect the common ancestry background. Here we describe the neuroanatomy of Hemigrapsus nudus (Malacostraca, Crustacea) focusing on optic lobe organization characterizing the medulla and lobula, the nested second and third synaptic visual centers. It is shown that unlike the equivalent region of insects, the malacostracan lobula is densely packed with columns that are distributed similarly to those in the medulla. Towards the medial side of the lobula, the dendrites converge into a thick bundle of axons that can be traced towards the midbrain. While similarities in neuronal organizations have been demonstrated to argue a monophyletic relationship between crustaceans and insects, differences in these systems could still indicate independent origins.