In a well of the island Antigua (West Indies) a species of Metacyclops was collected, related to M. hartmanni Herbst, 1960 and M. laticornis Lowndes, 1934. This new species, named M. janstocki is described and figured in both sexes. Both a differential diagnosis and a supplement to the key of Herbst (1988: 149-152) are given.