The twilight arthrothere resulted from populations of arthrothere that migrated into the twilight zone. The twilight arthrothere is more docile than its ancestor due to a wide variety of food sources that were not consumed by its main competitor: the thornant. Because of this, it no longer engages in extensive scavenging and kleptoparasitism. They are now grey so that they blend in with their environment. They also now have a sprawling stance, making it harder for them to be knocked over. In order to better navigate the dark waters of the twilight zone, the twilight arthtrothere has developed chemoreceptors within its antennae's claws, allowing them to navigate via 'scent'.
While the twilight arthrothere has a wide variety of food sources, it has a particular affinity towards consuming scavengers. This is because of the mutualistic relationship they have with the twilight euryptile. Because of their smaller size, the twilight arthrothere can eliminate scavengers that are too small for the twilight euryptile to properly attack or consume. This relationship decreases the number of scavengers feeding off of the twilight euryptile's carcasses and provides protection and food for the twilight arthrothere. This relationship began when some twilight arthrotheres found large numbers of small scavengers feeding off of guarded twilight euryptile kills. Because of the twilight euryptile's territorial nature, the scavengers' predators were either scared off or consumed, allowing them to congregate in large numbers around these kills. While the same happened to the original twilight euryptile population, some developed the ability to produce a 'scent' similar to that of the twilight euryptile. This allowed them to get close to the twilight euryptile and feed on the enormous amount of small scavengers.