Sertularella gayi is a colonial hydrozoan (family Sertulariidae, order Leptothecata) found in temperate coastal waters of the South Atlantic and Pacific, forming erect, branching thecate hydroid colonies on rocky substrates, shells, and macroalgae in subtidal habitats. Like other sertulariid hydroids, it produces gonotheca enclosing the gonozooids that release planula larvae or medusae for dispersal. Its wide southern hemisphere distribution makes it relevant to studies of temperate marine biogeography. Genomic data have been generated for this species and are available in public databases, enabling comparative studies of cnidarian evolution and ecology.