As the arthrothere continued to struggle under competition with the thornants, it radiated into different species. While some fled to the beach, others retreated into polar waters, where there was no competition to speak of. While these polar waters provided a brief refuge from the arthrothere’s struggle for survival, they would ultimately be driven out into temperate waters when the winter came. Forced to adapt further to the highly competitive coasts of east glicker, these arthrotheres would give rise to the migratory arthrothere.
The migratory arthrothere has finally grown large enough to access new, untapped sources of prey. Combined with their migratory nature, they flourish all across the southern half of Glicker. They primarily feed on paralixos, tentacle crystal tentacles, large knightworms, small colony crystal crystals, and krelp stalks. They also have been known to occasionally dig up and eat vinagobbles that they have stepped on. Their jaws now have a wider gape, allowing them to fit more in their mouth. Their antenna-limbs have been modified as well. The antenna-limbs now have an extra joint, allowing them to better maneuver them towards prey. Their cryptic coloration has given way to disruptive patterning with each segment altering between light and dark green. This coloration came about due to their segments being roughly the width of a colony crystal crystal. While they primarily catch and eat their own food, they will sometimes eat or steal carrion, as they have little trouble with scaring off other predators. With it occupying the same niche as its ancestor, the migratory arthrothere has replaced its ancestor within its range.
Due to their migratory nature, the migratory arthrothere has adapted towards being a better swimmer. Their fins have grown larger, and are highly effective when paired with the folded walking legs. In addition to this, their dorsal spikes have laterally flattened into fins, allowing for greater stabilization. This increased swimming ability allows them to cover more ground while migrating and reach the upper portions of krelp and tentacle crystals.