Stelletta ruetzleri sp. nov., a new ancorinid sponge from the Southwestern Atlantic (Porifera, Astrophorida), collected at 128 and 200 m depth off Rio Grande do Sul State coast, Brazil (31°20´-32°24´S/49°52´-50°15´W), is described and illustrated with SEM images of the spicules. The new species is based on the presence of one category of oxeas, dichotriaenes, oxyasters and spheroxyasters.