Convolutidae discoid to obcordate in shape; color results from pigments and symbiotic algae; often with two coexisting species of algal symbionts; brain insunk; mouth ventral and in posterior third of body; rhabdoids present; ovaries and testes paired; with sub-terminal male genital pore. Male copulatory organ composed of muscular seminal vesicle filled with sperm. Female gonopore present or absent. Seminal bursa with 2 or more (2–8) bursal nozzles. Statocyst and eyes absent in mature forms, but present in immature specimens. Frontal organ absent. Epizoic on corals.