Grasso, F.W.*; Basil, J.A.: Antennule Morphology and Olfactory Sampling strategy: Lessons from the lobster.

The six, paired cephalic appendages of decapod crustaceans provide sensory information to the highest centers of the brain. These bear sensory organs devoted to one primary and a number of secondary sensory modalities and allow these animals to actively probe and investigate their environment. Of these the antennules are specialized to provide chemical and rheotactic information. . We performed a morphological survey of 30 representatives of the Palinuridae (spiny lobsters). Across these species we found a 27-fold variation (estimated from morphology) in volume sampled by the olfactory sensilla (the aesthetascs) on these appendages. This contrasts with negligible variation in Nephophidae (clawed lobsters) and Scyllaridae (slipper lobsters) of comparable body size. We also found that the length of the antennules the covered by the aesthetascs on 23 species of spiny lobsters from the genus Panuluris does not scale in proportion to antennule length; the ratio decreased with increasing antennule length. Because the aesthetascs are located at the distal tips of the antennules, we suggest that the observed variation in olfactory sampling volume serves to increase the range of two-point discrimination rather than to increase the total receptor surface. We speculate that the variation may be accounted for by the flow regimes typical to each species niche.