Symbiotic bacteria produce defensive compounds found in their eukaryotic hosts, such as marine sponges. How these symbioses are formed in each sponge, their biodiversity, and their ecological roles in nature are open challenges that remain to be addressed. Here, we describe a candidate bacterial genus, Jaspinella sp., that harbors biosynthetic genes for the potent natural product toxin jaspamide (jasplakinolide) in the microbiomes of two geographically and taxonomically diverse sponge species, Jaspis (=Dorypleres) splendens and Dictyonella sp. The jas gene cluster in Jaspinella matches the expectation for jaspamide biosynthesis, including a nonribosomal peptide synthetase (NRPS) region homologous to the characterized chondramide cluster that produces a related compound in cultivated myxobacteria and a polyketide synthase (PKS) region that evolved convergently. Jaspinella is a member of Tectomicrobia, which consists of uncultivated bacteria including many well-known defensive sponge symbionts. However, Jaspinella is from a group previously associated only with soil and sediment bacteria, expanding the phylogenetic diversity of Tectomicrobia, the defensive symbioses in marine sponges, and knowledge of defensive compound evolution in nature.