Roygus

The roygus looks much like its ancestor. Its differences include a longer tongue-tentacle that is thicker than its ancestor's, especially at the tip, differences in average size and number of the metal nodules on its tongue, and a beehive-shaped upper shell. The metal nodules' differences are caused purely by genetic drift, but the other differences are adaptations for life along the banks of a flood-prone river. Much of its organ space is occupied by its massive digestive system, as before. Above that and inside the dome of the shell is a large pocket of air. When the river floods, this pocket of air helps keep the roygus afloat. It is further helped by the methane produced by its complex digestive system, for methane is lighter than air. The air pocket can consist of up to 12% methane with no harm to the roygus.

The roygus tucks in its limbs and seals its shell when borne by flood waters, but as the flood waters reside, it pokes out its tongue and paddles a short distance to a suitable spot. The tongue's thickened tip acts like an oar.

Surviving flood-based transport allows it to colonize new areas by the Yokto River, which explains its increase in range compared to its ancestor.

Modern royguses are found in the range shown.

(The earliest royguses lived in a place indicated by the red dot. From there, they were transported by flood to the Yokto Temperate Riparian and the other side of the Drake Temperate Rainforest's riverbank. This expanded range is indicated by the red border.)

Though their range is limited, throughout this range they are surprisingly common. In some places, nearly every rock stuck in the mud is actually a roygus. They live on the wood of live, dying, and dead lurspires, and can even live on 18 cm-long fragments of wood washed up on the river bank.