Unlike most terrestrial parasitengone mites (chiggers, erythraeids), known mostly from parasitic and easy-to-collect larvae, smaridid systematics are mainly based on the post larval instar. Larvae are rarely collected, and their biology and host associations are virtually unknown. Here we infer phylogenetic relationships of Smarididae based on 50 morphological characters using both larval and post larval instars, including data on the larval morphology of Trichosmaris obtained through rearing. The subfamily Smaridinae, as currently understood, was recovered paraphyletic: the genus Smaris was rendered as basal smaridid lineage, while the genus Fessonia (Smaridinae) was sister to Hirstiosomatinae, albeit with moderate support. Our analysis suggests that the genus SurasmarisSouthcott, 1995 is a junior synonym of TrichosmarisSouthcott, 1963 (syn. nov.), and two Sphaerotarsus species should be placed into Hirstiosoma: Hirstiosoma baenai (Mayoral & Barranco, 2017) comb. nov., Hirstiosoma quercus (Yazdanpanah, Saboori & Hakimitabar, 2016) comb. nov. Sphaerotarsus monticolusSouthcott, 1997 and S. leptopilus were recovered as independent lineages, and hence, a new genus Southcottiana gen. nov. is proposed to include Southcottiana monticola comb. nov (Southcott, 1997). We describe two new species, Trichosmaris paulensis sp. nov. (adults, larvae) and T. calcarensis sp. nov. (larva), and present the first description of larval T. dispar, the type species of Trichosmaris, previously known only from post larval instars. Based on the above results, we give a key to larval genera of Smarididae and a key to species of Trichosmaris (larval and postlarval instars).