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Abstract

Malacostracan crustaceans display a large diversity of sizes, morphs and life styles. However, only a few
representatives of decapod taxa have served as models for analyzing crustacean olfaction, such as
crayfish and spiny lobsters. Crustaceans bear multiple parallel chemosensory pathways represented by
different populations of unimodal chemosensory and bimodal chemo- and mechanosensory sensilla on
the mouthparts, the walking limbs and primarily on their two pairs of antennae. Here, we focus on the
olfactory pathway associated with the unimodal chemosensory sensilla on the
first antennal pair, the
aesthetascs. We explore the diverse arrangement of these sensilla across malacostracan taxa and point
out evolutionary transformations which occurred in the central olfactory pathway. We discuss the
evolution of chemoreceptor proteins, comparative aspects of active chemoreception and the temporal
resolution of crustacean olfactory system. Viewing the evolution of crustacean brains in light of energetic
constraints can help us understand their functional morphology and suggests that in various crustacean
lineages, the brains were simplified convergently because of metabolic limitations. Comparing the wiring
of afferents, interneurons and output neurons within the olfactory glomeruli suggests a deep homology
of insect and crustacean olfactory systems. However, both taxa followed distinct lineages during the
evolutionary elaboration of their olfactory systems. A comparison with insects suggests their olfactory
systems ö especially that of the vinegar
fly ö to be superb examples for “economy of design”. Such a
comparison also inspires new thoughts about olfactory coding and the functioning of malacostracan
olfactory systems in general.