The first record of the decapod, Pontonia pinnophylax, in Pinna nobilis from the southern Adriatic (Croatia) (Decapoda, Natantia).

While collecting Foraminifera shells from the bottom substrate around Pelješac Peninsula (southern Adriatic), the presence of Pontonia pinnophylax (Otto, 1821) in mussels, Pinna nobilis Linnaeus, 1758, living in Posidonia oceanica (L.) Delile sea grass meadows, was recorded. According to available data, it was obvious that detailed investigations of that species had never been made for the southern Adriatic. Ten samples of Pinna nobilis were obtained and only four specimens from the P. nobilis population were removed for investigation, from which eight individuals of Pontonia pinnophylax were isolated. The numbers and positions of the individuals were recorded. All of these were associated with their Pinna host in pairs, so the sex-ratio was 50% males and 50% females. Morphological study identified the left chela as the major chela in male shrimps. The largest host had the largest individuals of commensal shrimp. Total length appeared to be larger in male shrimps than in females. [ABSTRACT FROM AUTHOR]