Morphology and distribution of antennular setae of scyllarid lobsters (Scyllarides aequinoctialis, S. latus, and S. nodifer) with comments on their possible function

Abstract. Lateral flagella of the antennules of scyllarid lobsters were examined for setal morphology and distribution via scanning electron microscopy. Setal distribution patterns were mapped directly for 3 regions of the antennule ( base, tuft , and tip ) and analyzed for differences: (1) between left and right antennules, (2) between males and females within a species, and (3) among species by comparing counts of setae per annulus in the ventral tuft region only. Six types of antennular setae were identified based on their external morphology: aesthetases, simple, modified simple, asymmetric, hemi-plumose, and toothbrush setae. These different types were organized in a clear pattern over the ventral and dorsal surfaces of the lateral flagella of the antennule. Aesthetase, asymmetric, modified simple, and hemi-plumose setae were found only on annuli in the tuft region between the distal and proximal ends of the flagellum. Simple setae were found on all annuli of all regions of the antennule, and toothbrush setae were mainly concentrated on all annuli of the base region and on proximal annuli of the tuft region . All species of scyllarids examined had the same general pattern of setal distribution and no differences were found between left and right, or male and female antennules. Similar setae located on the lateral antennules of species from the families Nephrophidae and Palinuridae (clawed and spiny lobsters) have been previously described as chemo- and/or mechanoreceptive for use in distance chemoreception (i.e., detection and orientation to olfactory stimuli). Based on work on clawed and spiny lobsters, we predict that the aesthetases on slipper lobsters have a chemoreceptive function and that simple and toothbrush setae may have a bimodal chemo- and mechanoreceptive function.