Setal morphology, sexual dimorphism, and number of aesthetasc on the antennular lateral flagella of the red swamp crayfish Procambarus clarkii (Girard, 1852) (Decapoda: Astacidea: Cambaridae)

Decapod crustaceans primarily rely on various types of setal sensilla on their antennules to detect chemical and mechanical signals in the environment. Among these setae, the aesthetascs, located on the lateral flagella of the antennules, serve as the major olfactory receptors for detecting sex pheromones and recognizing both interspecific and conspecific individuals. Besides species-specific differences in setal type and aesthetasc number on the antennular flagella, there may also be sexual dimorphism within a species. We investigated the type and morphology of setae on the lateral flagella of the antennules of Procambarus clarkii (Girard, 1852) as well as difference in the aesthetasc number between males and females using scanning electron microscopy and optical microscopy. The overall anatomical structure of the olfactory ganglion associated with aesthetasc was described using paraffin sectioning. We identified 10 types of setae on the antennular lateral flagella, as well as sexual dimorphism in the aesthetasc number, the males having a significantly higher number compared to the females. The olfactory organ is composed of aesthetasc sensilla that house olfactory receptor neurons (ORNs), which are interconnected by neural pathways. The higher number of aesthetasc might corresponds to a higher number of ORNs, increasing olfaction sensitivity. The sexual dimorphism in terms of aesthetasc number between males and females provides a feasible morphological basis for understanding sexual selection in evolution.