[1] In traditional schemes, the family Diplomystidae was considered as the basal, primitive sister group to all other catfishes (Siluroidei) on the basis of morphological evidence.

Monophyly for Diplomystidae is well supported by synapomorphies of the vomerine and palatine shapes, cranial articulation of the hyomandibula, and heavily papillose skin.

[citation needed] Diplomystids are the only extant catfish family with teeth on a well-developed maxilla (although this is also true of the extinct genus Hypsidoris).

[5] Reproduction occurs at least during the austral summer based on captures of females with maturing eggs, and the juveniles reported here were collected in December.

[5] All diplomystids are considered to be potentially or actually threatened or endangered due to habitat deterioration and predation or competition by introduced trout, Oncorhynchus mykiss and Salmo trutta.