Holonema is thought to have been a benthic-dwelling fish, based on its cambered body shape, which performs better hydrodynamically when closer to the sea bed.

[1] Although previously thought to have fed in the bottom seafloor mud, more recent morphological studies of the jaw and toothplates suggest a more planktivorous lifestyle.

It is a fairly large species, though the type specimen is of an 18 centimeter long median dorsal plate belonging to a small individual.

[4] A large species from Givetian-aged strata in Novaya Zemlya, Russia, known only from two plates from one individual's trunk shield.

[4] H. bruehni is a recently discovered species from the Middle Eifelian-aged Brandenberg stratum of Sauerland, Northwestern Germany.

The median dorsal plate has a small, horn-like process, and the trunkshield is somewhat circular when viewed from the top or bottom.

Specimens and fragments from the Frasnian-aged Holy Cross Mountain of Poland, and the Givetian sections of the Fiskekløfta formation in Spitzbergen.