The Malacostraca (Crustacea) from a neurophylogenetic perspective: New insights from brain architecture in Nebalia herbstii Leach, 1814 (Leptostraca, Phyllocarida).

Abstract: In recent years, there has been a growing interest in synthesizing studies on the structure of the nervous systems with phylogenetic questions (“neurophylogeny”). However, in the discussion on the phylogeny of Malacostraca, and the question of their closest relatives, little attention has been paid to brain morphology in the basal representatives of this taxon. To close this gap in our knowledge, this study sets out to analyze the architecture of the brain of Nebalia herbstii (Leptostraca, Phyllocarida, Malacostraca) in a neurophylogenetic context. Most phylogenetic studies consider the Phyllocarida to be the sister group to the Eumalacostraca, together forming the taxon Malacostraca, so that the brain organization of N. herbstii may possess many ancestral features. Classical histological techniques and 3D reconstruction as well as immunostaining and confocal laser-scan imaging revealed that besides taxon specific characteristics, the brain organization of N. herbstii exhibits a strong eumalacostracan affinity. The four nested optic neuropils are connected by two successive chiasms. The olfactory globular tract, connecting the olfactory lobes with second order integration centers in the lateral protocerebrum, features a contralateral connection. The olfactory lobes are composed of a radial array of spherical/spheroid glomeruli but serotonergic innervations of the olfactory glomeruli are absent. These and other architectural features are discussed in comparison to the central nervous system of Eumalacostraca, Remipedia, non-malacostracan Crustacea and Hexapoda, and are synthesized into a ground pattern of the malacostracan brain that might serve as a basis for neurophylogenetic discussion of the evolutionary relationship of these taxa. [Copyright &y& Elsevier]