Morphology and Distribution of Antennal and Antennular Setae inLysmataShrimp

Abstract

In decapod crustaceans, chemical cues are usually detected by antennal and antennular setae. Different types of setae have been identified in various decapod species. In Lysmata shrimp, aesthetascs have been identified to be responsible for distance sex pheromone detection, whereas some other nonaesthetasc setae can detect contact sex pheromones. In this study, the morphology of antennal and antennular setae in six species of Lysmata shrimp was examined using scanning electron microscopy. The number of nonaesthetasc setae was counted and compared among the species with different social environments. Four types of antennal and antennular setae were identified, and their morphology was similar in all the Lysmata species studied. No sexual dimorphism was found in the morphology of setae. The total number of nonaesthetasc setae increased with shrimp size, whereas the density of nonaesthetasc setae did not change with growth. In general, the number and density of nonaesthetasc setae was greater in pair-living cleaner shrimp than in group-living and low-density peppermint shrimp, indicating that contact sex pheromones may be more important in pair-living species. Among peppermint shrimp, there were no significant differences in the number and density of nonaesthetasc setae between group-living species and low-density species, which suggests that social environments may not be the only factor that is related to the higher setae number and density in pair-living species.