A. marginatus is similar to A. obscurus in body size and shape of pronotum and elytra. In both species the integument is covered with lanceolate scales and setae, but in A. marginatus scales are mostly light brown and setae are slender, long and erect on the elytra. In A. obscurus scales are grey and setae are coarse, short and recumbent.
A. marginatus is a flightless species and the absence of males suggests that is probably parthenogenetic (Lanteri & Normark 1995).
A key to species of Atrichonotus is included in Lanteri & O'Brien (1990).
Associated to vegetation of the gallery forests of Paraná, Uruguay and La Plata rivers.