Pterophyllum leopoldi can be differentiated from other members of the genus by the presence of up to 11 vertical stripes on the body, though often only the 3 largest, boldest stripes can be seen. This species also shows a dark patch over the operculum.

In adult specimens, a red/maroon hue over the back and fins is characteristic of the species, leading some to believe the most colourful natural form Angelfish.

The name-sake roman nose possessed by the fish is also very distinctive and used as a meristic feature.

The smallest and most delicate of the nominal hatchetfishes. The rounded keel is shallower than related species, giving this fish a distinctive elongate profile.

The family Gasteropelecidae is separated from other Characiformes by the following combination of characters: front…

Despite its extensive natural distribution S. lilith is uncommon in the ornamental trade, where it is sometimes referred to as ‘one-spotted demon fish’ or ‘one spot eartheater’.

It can be distinguished from other members of the genus by possessing a single dark blotch on the flank and a prominent ocellus at the caudal-fin base. Among the named species it is most similar to S. daemon, but that species possesses two blotches on the flank.

Unfortunately diagnostic characters cannot be provided since we have been unable to obtain the type description to date, and little else has been written about this species.

There is also confusion regarding whether C. lamberti, the unidentified ‘C009’, and similar-looking fish collected close to Iquitos are conspecific or not. We include all together here until these issues are resolved.

Prior to description C. kanei was assigned the ‘C’ numbers C026 and C046.

Among congeners it is most easily-confused with, and sometimes traded as, C. atropersonatus, but can be identified by presence (vs. absence in C. atropersonatus) of dark markings in the anal and caudal fins, presence of numerous, smaller (vs. fewer, larger) dark spots on the body, and an overall darker (vs. paler) base colouration.

It can be distinguished from the majority of other Corydoras species by its distinctive colour pattern, comprising a uniform, lightish base pigmentation with a dark arched stripe extending over the upper portion of each flank, from the tip of the snout to the caudal-fin base. This is shared with a few congeners, however, including C. arcuatus, C. narcissus, and C. urucu.

Although described as a member of Corydoras this species was later moved into the genus Osteogaster by Cope (1894), but this was later synonymised with Corydoras by Gosline (1940).

It is sometimes confused with C. venezuelanus, while two similar-looking, unidentified fishes from Peru have been assigned the codes CW007 and CW043, respectively.

This species has been recorded from the Guaporé, Madeira, Branco, Trombetas, and Urubu river systems within the Amazon river basin, Brazil.

Type locality is ‘Igarapé Jatuarana, 5 kilometers above Samuel, Rio Guaporé, Rondonia, Brazil’.

Widely-distributed throughout the Amazon, Orinoco, Essequibo, and Tocantins river systems in Brazil, Peru, Bolivia, Ecuador, Colombia, Venezuela, and Guyana.

Type locality is ‘Rio Cupai [= Rio Cupari], Rio Tapajós basin, Amazon River drainage, Pará State, Brazil’.

This species is known from the rio Negro within the Brazilan Amazon basin and upper Río Orinoco system in Venezuela.

Type locality is ‘Rio Adujá, Rio Itú, tributary of middle Rio Negro, Amazonia, Brazil’.