Endemic to Southeast Brazil, this herbivorous, rheophilic, bottom-feeder only grows to around 4 cm (1.6 in) in length.

In reality, they belong to the species O. vittatus, O. vestitus and O. macrospilus and O. huaorani.

M. affinis is a Batesian mimic of Corydoras nattereri.

[2] M. affinis prefers an aquarium with fast moving water, sandy substrate, and plenty of hiding areas (old broken clay pipes is a preferred hiding habitat).

Preferred pH is slightly acidic with a tank temperature of 21–27 °C (70–81 °F).