The spaghetti bryozoan Amathia verticillata, formerly known as Zoobotryon verticillatum, was first described in 1822 from Naples, Italy, although this species was already present in 1807 at Cadiz, Spain. This ctenostome has long been considered a native species in the Mediterranean Sea but it has recently been suggested to be of Caribbean origin. It is most likely to have been introduced by vessels as hull fouling. This pseudo-indigenous species, i.e. a non-indigenous species (NIS) having been perceived to be native, has been found in several marinas and harbours within the Mediterranean Sea. In November 2014, this bryozoan species was abundant in the La Grande Motte marina on the south coast of France. Several thousand colonies were estimated to be present within this marina attached to the floating pontoon units that supported a floating boardwalk. Of the berthed craft examined, 31% were fouled with this species, and it was occasionally a prominent fouling species. Several macroinvertebrate species were associated with A. verticillata colonies, including some NIS, Paracerceis sculpta, Paranthura japonica and Caprella scaura, that are recorded for the first time from the Mediterranean coast of France. A. verticillata might support their transfer elsewhere by providing a habitat and substrate when attached to vessel hulls.