[4] In a 2004 study, different relationships among the callichthyines were found: Dianema and Hoplosternum form the most basal clade, and Callichthys is sister to Lepthoplosternum and Megalechis.

[5] There are currently four recognized species in this genus:[2] The genus Callichthys can be readily distinguished from other callichthyids by having the coracoids covered by skin and not exposed ventrally, the infraorbital bones also covered by skin, and the head highly depressed with less than 75% of the cleithral width (except sometimes in mature males).

[3] Callichthys is normally found in large schools on the muddy bottoms of slow-moving rivers, pools, drainage ditches, and swampy areas.

The walls of the gut are lined with tiny blood vessels into which the oxygen from the air can pass, similar to the function of true lungs.

Callichthys is a builder of bubblenests from plant parts, some bottom materials, and bubbles formed by a mouth secretion and air.