Unlike most other placoderms, the rhenanids' armor was made up of a mosaic of unfused scales and tubercles.

Another species of rhenanid was Bolivosteus chacomensis, of the Lower to Middle Devonian Malvinokaffric Fauna of Western Gondwana, in what is now Bolivia, South America.

There are five recognized species of rhenanids, in five genera, Asterosteus stenocephalus, Nefudina qalibahensis, Gemuendina stuertzi, Jagorina pandora, and Bolivosteus chacomensis.

[1] A sixth genus, Ohioaspis, is of questionable status, as the first specimens were ichthyoliths that were originally described as being tubercles from a new species of Asterosteus.

Later examinations of these tubercles have led to the formation of two camps of experts, one of which that believe the three recognized species of Ohioaspis were rhenanids, while the other suggests that they were actually some sort of ostracoderm agnathans.