Renilla reniformis, the sea pansy (family Renillidae), is a colonial pennatulacean octocoral found in shallow sandy habitats along the Atlantic coast of North America and Caribbean, forming distinctive kidney-shaped or oval disc colonies anchored in soft sediment. It is the biological source of Renilla luciferase (RLuc), which has become one of the most widely used reporter enzymes in molecular biology and cell imaging, enabling dual-reporter assays alongside firefly luciferase. A genome has been produced for R. Its luciferase gene has been cloned and expressed in diverse biological systems for research applications.