The Hidden Spiny Tree-rat is known from two sites in western Amazonas, Brazil. Some appearance and lifestyle details below come from descriptions of its genus, not direct species observations.
The genus is described as having coarse gray-brown spiny fur and a tail longer than the body, ending in a tuft. These are not presented as diagnostic traits unique to this species.
A genus overview describes Mesomys as arboreal, nocturnal, solitary, and associated with primary and secondary forest. This is not reported as direct observation of M. occultus.
An extinction-risk assessment has not been added yet.