Epactionotus is a genus of miniature armored catfish (family Loricariidae) in the dwarf-pleco subfamily Hypoptopomatinae, native to river drainages of southern Brazil and northern Argentina. The four atlas species are tiny even by loricariid standards, just 1.5 in as adults, with the flattened body, bony armor plating, and ventral sucker mouth typical of the family scaled down to fit life clinging to rocks and submerged wood in small streams.
Epactionotus gracilis, the slender cascudinho, is the one species in the genus with a recorded common name and reflects the group's local Portuguese nickname — cascudinho, meaning roughly 'little armored one' — used broadly for small hypoptopomatine plecos in Brazil. The genus has essentially no presence in the mainstream aquarium trade given its minute size and specialist habitat needs. Conservation data lean reassuring: three of the four atlas species are Least Concern, with the fourth not yet formally assessed.