In the interests of nomenclatural stability it is proposed that
Johnstonia Quatrefages, 1866 (Polychaeta, Maldanidae) be conserved relative to its senior homonym
Johnstonia Quatrefages, 1849 (Polychaeta, Nereidae) and its coexistent junior homonym
Johnstonia Basir, 1956 (Nematoda, Thelastomatidae). Type material of all species previously assigned to
Johnstonia Quatrefages, 1866 is re‐examined and a new species from Trinidad described. All three valid species (
J. clymenoides Quatrefages, 1866;
J. knysna Day. 1955;
J. duplicata sp. n.) are described and figured in detail. An unnamed fourth species is known only from fragments collected off West Africa, and
Johnstonia gracilis Kinberg, 1867 is newly synonymised with
Euclymene oerstedii (Claparède. 1863).