Cryptonanus guahybae is a small marsupial recorded in southern Brazil. Examined specimens had reddish-brown backs, while belly fur varied with age; collection records include flooded forest and sandy riparian forest.
All examined specimens had reddish-brown dorsal fur made of hairs with grey bases and reddish-brown tips. Ventral color varied from grey-based to self-colored; juveniles were more often grey-based.
Records from Rio Grande municipality were from the interior or edge of sandy riparian forest and from interiors and gaps in flooded forest. Captures were on the ground and in low vegetation.
An extinction-risk assessment has not been added yet.