South-Western Madagascar is considered to be a sponge biodiversity hotspot; however, current knowledge needs to be significantly enhanced. Homoscleromorpha are sponges mostly dwelling in poorly accessible cryptic habitats, and are currently experiencing a high rate of new descriptions after an increase in sampling effort. Before this study, seven homoscleromorph species had been reported in the region of Toliara, but four were erroneously assigned to cosmopolitan species. The aim of this work has been to revise the status of these species and assess the true Homoscleromorpha diversity in SW Madagascar. By applying an integrative taxonomy approach, this work presents six new Plakinidae belonging to four genera, one of them, Aspiculimerina gen. nov., being also new to science. Our findings definitively invalidate the record of Plakortis simplex in Madagascar, replacing it with Plakortis madagascarensis sp. nov. In addition, we reveal the strong probability that what was previously thought to be the occurrence of Plakina monolopha in Madagascar corresponds, in fact, to the Plakina rahelyae sp. nov., herein described. Added to the validated old data and the unrevised cosmopolitan species, these descriptions lead to 11 Homoscleromorpha species in SW Madagascar, making a total of 16 for the entire Western Indian Ocean, which thus becomes one of the richest bioregions for Homoscleromorpha.