The first record of external abnormalities in blue swimming crab Portunus segnis (Decapoda: Brachyura), from the Gulf of Gabes, Southern Tunisia (Central Mediterranean Sea)

The occurrence of a morphologically altered individual identified as Portunus segnis is reported in this note. An adult male of this species with an additional chela on the left cheliped, which could result in difficulties for reproduction and escape from predators. The cause of the malformation remains unknown, but the result are indicative that is most likely due to errors in morphogenetic processes.