A new red algal genus and species, Cresia opalescens D.L. Ballant., C. Lozada- Troche et H. Ruiz is described from coral reef habitats in Puerto Rico at 3 to 20 m depths. The new genus, whose reproductive and morphological characters all fall within those of Chrysymenia, possesses patterned and brilliant iridescence. Cresia opalescens produces small, simple vesiculate globose or peltate thalli, consisting of a single layer of medullary cells and two cortical cell layers. Gametophytes are dioecious. Cystocarps protrude slightly and measure 270-320 μm in diameter. Spermatangial mother cells are produced in periclinal series, and divide to produce spermatangia. Ovate tetrasporangia are scattered in the cortex. are cruciately divided and intercalary, measuring to 20 × 25 μm. Molecular evidence indicates that this alga is positioned within the Erythrocolon group of the Rhodymeniaceae.