Malacostraca

AbstractThe central nervous system (CNS) of malacostracan crustaceans (e.g. shrimp, crayfish, lobsters, crabs, stomatopods, isopods, amphipods) is an arthropod-typical ventral nerve cord with fused anterior ganglia forming a brain and a suboesophageal ganglion. The brain contains two prominent pathways for sensing distant objects, the visual and the olfactory pathway, which in their overall organization are highly similar to corresponding sensory pathways in the insect brain. Neuropils with distinctly different structure serve both pathways: the neuropils of the visual pathway are organized into retinotopic columns, the neuropils of the olfactory pathway are organized into glomeruli (first synaptic relay) or microglomeruli (second stage core neuropil). Both pathways are devoid of innervation by motor neurons and thus do not participate directly in controlling motor output. The brain, the suboesophageal ganglion, the thoracic ganglia, and the abdominal ganglia contain bilaterally symmetrical neuropils that receive chemo- and mechanosensory input from sensilla on the segmental appendages and serve as local motor centres of these appendages. These neuropils are structured into transverse units indicative of somatotopic information processing and they provide the neuronal substrate for direct sensory–motor interactions. Integration of multimodal sensory information and coordination of movements of different segmental appendages is mediated mainly by unstructured neuropils of the medial and lateral protocerebrum of the brain. As insects evolved from crustaceans, a deeper understanding of the functional neuroanatomy of the malacostracan CNS promises to reveal the trajectory of the evolutionary changes shaping the CNS of insects and making them the most successful terrestrial arthropods.