Anthropogenic spread of the immigrant sea-spider Ammothea hilgendorfii (Arthropoda: Pycnogonida: Ammotheidae) in UK waters

The ammotheid pycnogonid Ammothea hilgendorfi was first recorded outside its native range of the Pacific Ocean in 1978 in southern England and in the Lagoon of Venice in 1979 to 1981. Both occurrences are attributed to anthropogenic dispersion by shipping. Subsequently, it has spread further in the UK to Dorset and, most recently, to Essex. The world distribution of this species and the history of its occurrence outside the Pacific are reviewed, and hypotheses for its recent spread in the UK, via recreational boating, are presented.