Hermit Rat

The Hermit Rat is a species that inhabits the city areas of the 6th layer of the Abyss.

Description
Due to their bodies being shaped by their elastic bones they are able to fit into tight spaces and their sturdy fangs help them to shape the inside of their dwellings, which ranges from various ammonites to lost delver helmets.

It's theorized the reason why they use objects as dwellings is in order to camouflage themselves from the various predators of the 6th layer.