Rainbowhedrons replaced their ancestor, the Binucleus Stella Dodecahedron, as they spread far and wide across the oceans of Sagan 4. Rainbowhedrons all have the shape of a dodecahedron, which consists of the outer photosynthetic shell. This shell is now reinforced by silicate cell walls. These photosynthetic shells still contain several photosynthetic pigments and are able to switch between them. The exact complement varies by species, but they typically range from green, for shallower water, through yellows and reds, to especially dark reds for their deepest extents.
Within the shell is the fungal core. Technically separate organisms, the shell and core nonetheless operate as a unit. The core digests dead organic material, which enters through pores in the shell.
However, one significant change from their ancestors is that rainbowhedrons now have large empty chambers inside the shells, which they can fill with air to adjust their buoyancy. The configuration of these chambers varies by species, as does their behavior. It is common, however, to stay near the surface during the daytime and sink during the night.
These chambers also provide a convenient location to grow offspring. The shell and core bud off new cells, which may go directly into a chamber or float off through the open ocean, eventually taken in by another rainbowhedron. After exchanging genetic material with each other, these cells will form into a miniature rainbowhedron and exit through a pore.