Structure of Aesthetascs in Selected Marine and Terrestrial Decapods: Chemoreceptor Morphology and Environment

We have compared the structure of the aesthetascs—thin-walled chemosensory pegs on the antennules—of Coenobita, a terrestrial hermit crab, and of various marine decapods, including the aquatic hermit crab, Pagurus hirsutiusculus. In all cases, the aesthetascs are innervated by the dendrites of many bipolar neurons whose cell bodies are grouped beneath the bases of the hairs. The dendrites have basal bodies and cilia that divide into slender branches, each distinguished by ovoid swellings along its length and containing one or more microtubules apparently continuous with the microtubules of the cilia. The arrangement of the dendrites within the aesthetascs is distinctly different in Coenobita from that in the marine animals, even in its relative, Pagurus. There are many points of structural convergence between the aesthetascs of Coenobita and the thin-walled olfactory pegs of the insect antenna. These modifications may represent adaptations for conservation of water in the terrestrial receptors.