Carpetesta
One offshoot of C. linkteneresca migrated eastward into the shallow seas. There, they found the ocean floor to be a convenient surface to settle on. As their range extended into less populated regions, they became less active filter-feeders. Instead, they would eat whatever organic material rained down upon them: mostly dead cells, though they would catch the occasional unwary live one.
Like their ancestor, carpetestas consist of clumps of about four cells, each cell bearing a tentacle, which reaches outward. Also like its ancestor, these tentacles are used to connect with other clumps, forming an extended network in which each individual clump is held at a distance. However, these tentacles no longer serve as baits, being repurposed so that their connective function is primary. These connections can transfer material from cell to cell; usually nutrition, but they can also transfer genetic material and even organelles.
These connections allow carpetesta to extend into a large grid, the links forming the shapes of squares. This forms an extremely thin and spread out film over a solid surface. Cell clumps reproduce by binary fission, each of the four cells splitting at the same time to form a new group of four. When this happens at the edge of the film, the new clumps may connect onto the end, further expanding the grid, or may drift away and find another surface to colonize, or even join a different film elsewhere (thus providing an infusion of new genetic material). Films from separate sources may also come in contact by growing into one another and merging, thereby providing another source for genetic exchange. In theory, there's no limit to how widely a film could spread, but in practice they will be broken up by upheavals, waves, crawling organisms, etc.
However, when clumps in the middle reproduce, if the offspring remains nearby, they will begin to form a new grid on top of the old one, in a separate layer. Due to the large amount of open space between clumps, it is possible for several layers to stack on top of each other. These stacked layers are mostly independent from each other, but their tentacles will sometimes switch around to feed from one layer into another, and the upper layers will secrete processed food down to the lower ones. Generally, the upper layers will be slightly more active, and filter-feed more, while the lower layers perform the final stages of decomposition, but this is only determined by cells responding to stimuli in their environment, not any kind of set specialization.
Thus, they form a filmy carpet upon rocks, the ocean floor, or wherever they can find a stable home.
As they share their range with clingowhexia, which reside on the same sorts of surfaces, they frequently interact. Clingowhexia are one of the most likely food items for carpetestas to pick up while filter-feeding, when hopeful juveniles attempt to settle on a surface, only to find it already occupied by a devouring carpet. Free-swimming carpetesta clumps, however, are likely to fall prey to the larger individual clingowhexia cells.
On the other hand, lucky clingowhexia may settle within the gaps between carpetesta clumps, leading to a common pattern in which a microbial film consists of mingled carpetesta layers and clingowhexia, only occasionally eating one another.