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

Abstract

This study describes the morphology and distribution of setae on the lateral flagella of the antennules of three species of scyllarid (slipper) lobsters. Setae were examined using Scanning Electron Microscopy and their distribution patterns were directly mapped for three regions of the antennule (base, tuft, and tip). The distribution pattern was then analyzed for differences between left and right antennules and males and females within a species, and then among species by comparing counts of setae per annulus in the ventral tuft region only. Parsimony analyses were conducted on setal distribution data compiled from the entire antennule for each individual of the three species to resolve the relationships among the species. Using a modified version of Watling s scheme for setal morphology, six types of antennular setae were identified based on their external morphology: aesthetascs, simple, modified simple, asymmetric, hemi-plumose, and toothbrush setae. These different types were found to be organized in a clear pattern over the ventral and dorsal surfaces of the lateral flagella of the antennule. Aesthetasc, asymmetric, modified simple and hemi-plumose setae were only found 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 had the same general pattern of setal distribution and there were no differences found between left and right, or male and female antennules. The parsimony analyses provided little resolution indicating that there was general overlap in the number and distribution of setae among the three species. Similar setae located on the lateral antennules of species from the families Nephrophidae and Palinuridae (clawed and spiny lobsters) are chemo- and/or mechanoreceptive and are used for distance chemoreception (olfaction). Given the similarity in structure to these previously described setae, it is almost certain that the aesthetascs on slipper lobsters have a chemoreceptive function and that the simple and toothbrush setae described most likely have a bimodal chemomechanoreceptive function.