A new species of Eutrachytes (Eutrachytes flagellatus) is described based on a complete ontogenetic series, starting from larva and including the adult female and male. This Uropodina mite was isolated from the pneumatophore surface of Avicennia officinalis having algal (Bostryschia sp.) growth in Goa, India. Notable morphological attributes peculiar to immature instars of this species include a flagellate tubular dorsolateral respiratory structure extending from the peritreme, nude pygidial shields in the adult male and female and a deep concave formation at the posterolateral margins of the dorsal shield. A taxonomic discussion with salient diagnostic features of the genus is given and a key to genera of the family is presented. We present two nomenclature modifications: Deraiophoridae syn. nov. as the junior synonym of Eutrachytidae and Dentibaiulus Hirschmann, 1979 syn. nov. as a junior synonym of Eutrachytes Berlese, 1914. A compiled list of all new species discovered to date from mangrove roots in different parts of the world is given