First records in the East Atlantic are reported for the North-West Atlantic endemic mysid Neomysis americana
(S. I. Smith, 1873), previously known as an invader of South-West Atlantic coasts. Two specimens were caught in 2010 in
coastal waters of The Netherlands. The new records provide the first evidence for a west to east transfer of a mysid
species across the Atlantic, whereas previously published transfers were observed only in the opposite direction. Major
diagnostic characters are reconsidered and the validity of the European species of Neomysis and Acanthomysis is
discussed. A pictorial key to these species is given to facilitate future assessments of potential range expansions of N.