Sphenopus marsupialis is a solitary zoantharian (family Sphenopidae, order Zoantharia) found in shallow sandy and muddy substrates across the Indo-Pacific and Mediterranean, unusual among zoantharians in being solitary rather than colonial and living partially buried in soft sediments with only the oral disc exposed. Its single, large polyp can incorporate foreign particles from the substrate into its body wall. Its ecology and systematic position within Sphenopidae are important for understanding zoantharian body plan evolution. Genomic data have been generated for this species and are available in public databases, enabling comparative studies of cnidarian evolution and ecology.