Siltsifter
Splitting from its ancestor, the siltsifter has further evolved to exploit a subterranean lifestyle. Possessing a smoother, narrower exoskeleton compared to that of its kin, its powerful spade-like forelimbs allow it to quickly tunnel through the sand as it searches for small bits of detritus to consume. With no natural predators, their numbers have exploded, which had led to most beaches throughout Dixon to have populations that are millions strong. Such a population size has affected these regions as well, as their constant burrowing helps to aerate the sand to a small degree, while their waste provides nourishment for various coastal flora and microbes. At night, while under the light of Mason, siltsifters will often surface in order to scavenge corpses that have washed ashore, thus helping to keep the beaches clean.
Unlike their various kin, the siltsifter have actually become more reliant on the ocean over time in order to survive. Their gills are still retained into adulthood, but the siltsifter has otherwise undergone atavism. The gill-chambers are no longer connected to their lung-chambers. The two pairs of spiracles attached to these lung-chambers still remain and still hidden within the seam in-between the lung plate - notable for its rich purple hue - and torso plate. The lung chambers have once more been divided by a septum. The gill-chambers must be periodically moistened with water, lest they otherwise become desiccated and thus nonfunctional, which would be fatal due to the resulting suffocation that would ensue. As an exposed gill opening would have proven a problem for a subterranean lifestyle, so the species has evolved to counteract this with the evolution of tiny gill flaps that cover them. These gill flaps are supported by bony internal structures, not unlike that which makes up their exoskeletons, and contain a rich supply of blood vessels that tint them purple in color. These flaps aid them by preventing sand and grit from becoming lodged within the gill openings. Other than this, the respiratory system functions similarly to that of its ancestors.
Reproduction occurs throughout the year, and the eggs resulting following fertilization are released into the water during high tide so that they may be carried out into the open water with the currents. The larvae that inevitably hatch from these eggs will stay within the open waters, feeding on free-floating bits of detritus until they are both large and developed enough to settle onto the shores of the beaches and begin digging tunnels on their own. This dispersal method has led to the colonization of Fermi island by larvae that, while floating in the Dixon-Fermi Subtropical Sea, were carried over to the shores of that adjacent landmass. It did not take long following this for healthy populations of siltsifters to establish themselves there.