Sex with the lights off: Can a morphological structure reveal the sex and functional sexual maturity in the genus Plesionika?

Abstract

The present work describes a taxonomic trait able to determine sex in pandalid shrimps of the genus Plesionika and an indicator of functional maturity in females. This structure is described as formed by two teeth with abundant setae present in all males of the nine Plesionika species examined. This morphological trait has been ignored across the taxonomy in pandalids. Thoracic teeth were located on the 7th thoracic sternite. Each species presents a characteristic trait of this structure, although P. williamsi has a particular pair of thoracic teeth compared with their congeners. This structure could be used as a tool in the systematics of this genus. Sex determination through thoracic teeth shall represent a faster alternative to the classical appendix masculina sexing method. Functional maturity of females is linked to the fading of immature thoracic teeth. The observation of living specimens in tanks has allowed for the finding that males of P. narval and P. edwardsii actively seek (search for) females and use their third pair of multi-articulate legs to locate the teeth of the thoracic region, which implicates these structures in the activity of “pure searchers” to locate mature females. Thoracic teeth open a new window to different fields of research, such as taxonomy, systematics, and sexual behaviour, and are a tool to determine the first maturity of the Plesionika species.