Representatives of all genera and subgenera of Haliplidae are examined regarding the shape of the air storage under the metacoxal plates. Three different main types can be distinguished with strong variation in the species of Haliplus. In general the results support the present concept of genera and subgenera, but a few exceptions are found. The subgenus Phalilus is raised to genus level. The genera Algophilus Zimmermann and Apteraliplus Chandler are reduced to subgenera of Haliplus Latreille. The synonymised genus Haliaplus Ádám is re-installed as a subgenus of Haliplus. Three new subgenera are introduced: Australiplus, Borealiplus and Nipponiplus. A cladistic analysis is carried out using 27 characters including those of the metacoxal air-storage space. A cladogram to subgenus level is presented.