Volvocine algae are a staple of Apterran oceans, taking the niches left open as a result of the planet's lack of diatoms. Unlike their unicellular analogs, these phytoplankton reach macroscopic scales - even on Earth, their colonies can number in the tens of thousands of cells, and some Apterran lineages are now several centimeters in diameter. At such scales, the algae cannot survive without a solid support system. In the case of Vitrovolvox, this issue is solved with a rigid shell. Like diatoms on Earth and sea hydras on Apterra, this plant-like organism builds its hard parts out of silica. This exoskeleton is built by specialized "vitroblast" cells, which do not photosynthesize and die off after growth is complete. Vitroblasts originated as a means of attaching to sediment, as all Vitrovolvox have abandoned a free-floating lifestyle and now live in the benthic zone.
Vitrovolvox physically resembles a massive Volvox colony, with an orderly structure of body cells arranged in a lattice. These vegetative cells form a single layer pressed against the glass. They serve to create a strong second-order membrane that keeps the fluid within the colony mostly distinct from the surrounding seawater. The membrane contains relatively few chloroplasts; most photosynthesis is performed by cells that float freely in the interior. Also drifting around this intercellular soup are reproductive cells that grow into new colonies, resulting in smaller spheres contained within the mother alga. However, with a solid glassy shell surrounding the entire organism, additional adaptations are necessary for these daughter colonies to disperse. This is typically achieved with small pores that the growing offspring can squeeze out of before their own shells develop. These are accompanied by stomata-like openings in the structural membrane that can be opened and shut at will. Most species, like Baublewort (V. globulus), have hundreds of such pores, formed along suture lines where smaller plates of glass fuse during development. The pores on the colony's underside also allow the root-like holdfast organ to reach the substrate below.
One variation on this strategy is employed by the Shatterbloom (V. concutus), which has only two growth plates that fuse along a single line, dividing the shell into left and right hemispheres. The pores are small, numerous, and arranged in a perfectly straight line that serves as a natural breaking point. When this alga is ready to reproduce, it builds pressure inside its membrane as its daughter colonies grow. Then the mature Vitrovolvox ends its reproductive cycle in violent fashion, jettisoning its shell and projecting its offspring in all directions. Species like this one are most common in shallow, slow-moving waters where dispersal is difficult, or in seasonally productive environments where it would be disadvantageous to produce smaller numbers of new colonies over time. This explosive birth-giving process does not necessarily kill the shatterbloom, as it maintains a small reservoir of undifferentiated cells within its holdfast that can develop into new vitroblasts after reproduction (or if the colony is damaged in any way), regrowing its shell. Then, other totipotent cells begin dividing and specializing into membrane, photosynthetic, and reproductive cells, quickly restoring the Vitrovolvox to full health.