Domed Photosagnia split from its ancestor, Darwinian Photosagnia, which would occasionally drift north onto the East Darwin Temperate Beach. In this more competitive environment, colonies developed primitive cell differentiation triggered by environmental cues within the mats. Surface cells are more specialized for photosynthesis, those inside have more water storage which allows survival further from the shore, and those at the bottom and edges are more detritivorous to capture organic matter and available nutrients.
These adaptations allow mats to spread several meters beyond the high tide line, avoiding competition and predation. The drier conditions of the inner beaches cause mats to have thicker cell walls, more water storage cells, and a more compact, round dome shape. Otherwise, they are much like their ancestor and can survive as free-floating single cells in seawater.