The species inhabits the Fynbos and Nama Karoo biomes, where it constructs retreat-webs underneath rocks.
Description
Only females of Penestomus planus are known to science. The carapace is orange, lighterposteriorly with a smooth texture, covered by fine black setae with broad white setae concentrated in the thoracic and fovea regions. The sternum is pale yellow. The chelicerae are dark red with six promarginal teeth and two retromarginal teeth. The legs are dusky yellow basally, with anterior legs orange distally and posterior legs yellow distally. The opisthosoma appears pale, but details are obscured due to specimendamage.