Crustaceans express at least three classes of putative chemosensory proteins. These are: Ionotropic Receptors (IRs), derived from the heterotetrameric ionotropic glutamate receptors (iGluRs) Transient Receptor Potential (TRP) channels, a diverse set of sensor-channels that include several families of chemosensory channels and Gustatory Receptor-Like receptors (GRLs), which are ionotropic receptors that are homologues of Gustatory Receptors (GRs) of insects and are expressed sparingly in most decapod crustaceans studied so far. IRs are typically numerically the most dominant of these receptor proteins in crustaceans and include two classes: four co-receptor IRs, which are necessary for making a functional receptor-channel and tuning IRs, whose specific combination in the IR subunits in the heterotetramer confers specific chemical specificity. In order to study the expression of these families of chemosensory proteins in decapod crustaceans, we examined and compared the transcriptomes from two major chemosensory organs - the lateral flagellum of the antennules (LF) and the tips of the legs (dactyls) - of the Caribbean spiny lobster Panulirus argus, the clawed lobster Homarus americanus, the red swamp crayfish Procambarus clarkii, and the blue crab Callinectes sapidus. We also compared the transcriptomes generated from the brains of P. argus, H. americanus, and P. clarkii. Each species has at least circa 100 to 250 IRs, 1 to 4 GRLs, and circa 15 TRP channels including those shown to be chemoreceptors in other species. The IRs show different degrees of phylogenetic conservation: some are arthropod-conserved, others are pancrustacean-conserved, others appear to be crustacean-conserved, and some appear to be species-specific. Many IRs appear to be more highly expressed in the LF than dactyl or brain. Our research shows that decapod crustaceans have an abundance of chemosensory proteins of different types, phylogenetic conservation, and expression patterns. An understanding of their functional roles awaits determining their expression patterns in individual chemosensory neurons and the central projections of those neurons.