Split off from the Sayceback, the Riversaycer followed mosshrooms into Seal and became freshwater. It is generally pretty similar to its ancestor, though its raptorial arm has shrunken from disuse and genetic drift has resulted in a dark-colored beak. It is a somewhat better swimmer, being capable of short bursts of speed by “running” through the water with its flat leg-like fins, but it still largely prefers walking on the sediment. To better support its weight in the less dense freshwater, it has developed a “ribcage” consisting of cartilage rings extending from the internal side of its shell and converging on a modified sternum-like cartilaginous raptorial arm bone on its underside. This also provides more muscle attachments for its limbs and helps protect its internal organs if it were to be attacked. Additional V-shaped structures, called “chevrons” for their similarities to real-world tail ribs, run down its anal arm and up its short neck, providing additional support and muscle attachment so that it is not easily torn apart by predators.
The Riversaycer’s keratinous features have been altered. Though the changes are not externally visible, the structure of all keratin in its body has been altered into a stronger, more chitin-like structure. This modified form of keratin is called “saycer keratin”, and it is unique to the Riversaycer and any of its future descendants. The benefit of this is that the modified keratin is stiffer and less likely to split and tear than ordinary forms of keratin, which in turn both increases the effectiveness of its shell and makes its bite much stronger. Its beaked jaws also now contain a similar bone-like material to that in its shell, serving as muscle attachments so that it has finer control over the movements of its beak.
The Riversaycer has eliminated the need to filter-feed as a juvenile, with juveniles instead feeding on the abundant, easy-to-eat Violetmellow; adults, too, consume this, though only when mosshrooms are unavailable. The Riversaycer has a radial fetal stage, but becomes bilateral before hatching. Its eggshell is made of living cells, and unhatched babies feed on a yolk-like substance. Like its ancestor, the Riversaycer mates by “holding hands” using its flexible, tentacle-like anal fingers to bring the respective male and female cloacas together.
The Riversaycer's skeleton, uncolored
The Riversaycer's skeleton, colored. White represents bone, grey cartilage.
The Riversaycer's skeleton, colored. White represents unchanged from its ancestor, orange for modified from its ancestor, and blue for brand new.