From the Pacific Ocean to the Mediterranean Sea: Watersipora arcuata, a new non-indigenous bryozoan in Europe

This study reports the first record of the cheilostome bryozoan Watersipora arcuata in the Mediterranean Sea, namely in a marina of the Ligurian Sea (Italy), during two monitoring surveys carried out in 2013 and 2014, representing to date the first European finding. The species, whose native origin is deemed to be the Tropical Eastern Pacific region, was already reported as being introduced to California, Australia, New Zealand and Hawaii, but not outside the Pacific Ocean. The genus Watersipora includes 13 species of encrusting bryozoans, difficult to distinguish using simple visual clues and usually requiring careful morphological measurements, with appropriate microscopy methods. A detailed taxonomic description of W. arcuata is provided here, in comparison with the similar species W. nigra and W. platypora.