Quataetar
With the rise of the Trisymbiomats, the Helmetstar populations in the south adapted to fill the niche opened up by this readily available food source.
Their feeding behaviors have changed somewhat from their ancestors. They lazily roam the coastal floor, grazing the mats of flora as they pass over top. They no longer stand stock upright, instead choosing to slither along the floor as a means of conserving energy. Once they detect food, they with move their limbs in a "snow angel" pattern, loosening enough flora for them to pull into their mouths.
With the advent of this new behavior, the Quataeter had to develop methods to protect their gills. With their gills on the underside of their bodies, they are pressed to the seabed whenever they feed. As a result, they can only feed for short bursts before they have to stop to reoxygenate. While not feeding, however, they have their bodies' centres slightly raised, and their thickened flagella have begun to act as a quasi podia, which allows for the free flow of oxygenated water underneath their bodies towards their gills. They have become so plentiful off this new food source, that over time the populations were able to move north and outcompete their ancestors entirely.