[1] Fossils have been found from the Czech Republic near the towns of Plzeň, Nýřany, and Třemošná, and date back to the Middle Pennsylvanian.

Two species belonging to different genera, Seeleya pusilla and Orthocosta microscopica, have been synonymized with H. longicostatum and are thought to represent very immature individuals.

The skull of Hyloplesion superficially resembles that of the unrelated romeriid reptile Romeria in lateral view due to similarities in the pattern of the dermal bones and the hooked shape of the premaxilla.

[1] A range of morphological characteristics makes it difficult to determine whether Hyloplesion was primarily terrestrial or aquatic.

[1] Although the digits are well ossified, the reduced number of toes in Hyloplesion is seen as an adaptation for an aquatic lifestyle.