Can a morphological structure be used as a macroscopic indicator of sexual maturity in deep-sea shrimps of the genus Plesionika?

Abstract

The present work describes a new structure present in the genus Plesionika that enables sexual maturity determination in females and the sex determination in mature pandalids of the genus Plesionika and Heterocarpus. Females of P. edwardsi presented sizes ranging between 14.10-19.05 mm CL and the spines, located between the 5th pair of pereiopods, were present until 17.45 mm CL. In this species the individuals reach the size of first maturity (SFM) at 17.65 mm CL. On the other hand, the size in P. gigliolii ranged between 11.21-12.13 mm CL. P.giglioli reached SFM at 8.23 mm CL and the spines were present until 11.41 mm CL. In the case of P. narval the size ranged between 12.94-19.72 mm CL and the spines were present until 14.45 mm CL, which matches with the SFM at 14.61 mm CL. Finally, size in females of P. williamsi ranged between 18.05-29.56 mm carapace length (CL) and spines were present until 18.34 mm CL. The SFM in this species is 18.00 mm CL. The correlation between the presence or absence of spines in females of genus Plesionika and the stage of development (immature or mature) of the ovaries in the histological study was validated. Observation in tanks has allowed finding that males of P. narval and P. edwardsii actively seek females and use the third pair of multi-articulate legs, in addition to grooming and to catch food, to locate spines of the thoracic region: if a male detected the spines (male-male interaction) contact was abruptly interrupted, whereas if not detected (male-female interaction) courtship began.