Species of Pseudacanthicus are large, spiny loricariids with a diverse range of colour patterns. Colour is from light to dark gray, often with black spots. The fins and body may have red sections or a red wash. Colouration varies between rivers and can also change throughout the lifetime of a single individual. The abdomen is covered in small plates in adults.
The caudal fin is forked, but without filaments. The jaws are short, forming an acute angle at their union; the teeth are few and stout. The adipose fin is present. In the aquarium, Pseudacanthicus species may be kept in the aquarium. P. leopardus is a large attractive fish known in the aquarium hobby as the leopard cactus pleco.
It is a large fish that essentially feeds on dead meat. It is territorial and care should be taken when maintaining it with other large, nocturnal fish.