Tweedy's crab-eating rat is a rarely recorded, water-associated rodent. In 2021 it was observed at a pond on Ecuador's coast; the individual had gray-brown upperparts and a whitish to yellowish-gray underside.
The 2021 individual had gray-brown upperparts, a white to yellowish-gray underside, and a uniformly dark tail.
The species is described as semiaquatic and nocturnal. The paper's individual was found at a pond in a botanical garden on Ecuador's coast.
An extinction-risk assessment has not been added yet.