The morphology, relationships, and classification of the Tethinidae and Canacidae are considered, with special reference to the Zaleinae. Homologies of bristles near the vertex of the head are critically appraised, and the origin of the sclerite known as the prelabrum or anteclypeus is considered. The family Canacidae Jones, 1906 is classified into the following six subfamilies: Apetaeninae Mathis & Munari, 1996; Canacinae s.str.; Horaismopterinae Sabrosky, 1978; Pelomyiinae Foster, 1976; Tethininae Hendel, 1916; Zaleinae D. McAlpine, 1985. The family name Tethinidae thus becomes a new subjective synonym of Canacidae. The subfamily Nocticanacinae Mathis, 1982 becomes a tribe Nocticanacini n.stat. of Canacinae. Tethinosoma Malloch is transferred from the Tethininae to the Horaismopterinae. A key to subfamilies of Canacidae s.l. is given. A revised characterization of Zaleinae is given and its two genera and c. 16 species are keyed. Revised characterizations of Suffomyia Freidberg and Zalea D. McAlpine are given. The following new species are described: Suffomyia sabroskyi (Caroline Islands); Suffomyia ismayi (New Guinea); Zalea earlyi, Zalea johnsi, Zalea lithax, Zalea mathisi, Zalea ohauorae, Zalea uda, Zalea wisei (New Zealand); Zalea clava (Western Australia); Zalea dayi (New South Wales). Two doubtful species represented by inadequate material are assigned provisional numbers. Adults of these maritime flies were found on shoreline rocks or on stranded "seaweed". Parasitism of four Zalea spp. by laboulbenialean fungi is recorded. Collection techniques for zaleines are mentioned.