The inconspicuous hydrozoan Clytia hummelincki, first recorded from the Mediterranean Sea in 1996, is presently widespread throughout the middle Mediterranean Sea and the Adriatic Sea. Two surveys carried out in 2003 and 2004 along the coast of the Salento Peninsula, Italy, showed that this species inhabits a belt between 0.5 and 2 m depth in sea urchin barrens and in areas damaged by date mussel fisheries. The comparison between the two surveys indicates that the frequency of the alien increased from 2003 to 2004. The life cycle of C. hummelincki is described for the first time.
