Herein, we present morphological and genetic evidence of the presence of the exotic calcareous sponge Heteropia glomerosa (Bowerbank, 1873) on the northern coast of the state of São Paulo. We also report its occurrence on natural substrates in the region and a case of the sponge living in association with the cryptogenic ascidian Phallusia nigra Savigny, 1816—an ecological interaction never before mentioned in the literature. Previous records of H. glomerosa in Ilhabela and São Sebastião were restricted to artificial substrates, such as PVC panels. Furthermore, earlier studies along the Brazilian coast have indicated that its colonization occurs more frequently on artificial substrates, such as ropes, wood, plastic, concrete, and docks within marina and port areas. All the new records presented here are from beaches that have never been sampled before, including Ubatuba as a new locality. Additionally, this finding on natural substrates represents an advance in the knowledge of its distribution and serves as an alert to the potential expansion of this species to the southern coast of São Paulo. Further investigations into ecological aspects are necessary to understand the processes favoring geographical expansion and ecological interactions with native species. Therefore, it is essential to assess the ecological role of H. glomerosa in the environment by implementing long-term monitoring actions.