The specific epithet arenarum is derived from the Latin word for "sand", "arena", to reflect the sandy soils of the species' main habitat.

Adult males have mostly dark gray upperparts that are darkest on their forecrown and lightest in the center of their back.

It grows on white sand soils and is characterized by a stunted canopy and dense undergrowth.

The western sub-population occurs in a similar forest type (irapayal) on both sandy and weathered clay soils and that is taller with a different understorey plant community.

It typically forages in pairs or in family groups in dense vegetation, mostly on the ground and within about 1 m (3 ft) above it.

The Allpahuayo antbird's song is "a moderately paced, slightly decelerating series of monotone whistles usually with a stuttered, higher-pitched introductory note: hi'hi hew-hew-hew-hew-hew-hew-hew".

Its calls include "a descending whine or whistle, a harsher tchah, a rising, melodic k'lee?

It has a small range; its "uncommon and local" population is estimated at between 600 and 1700 mature individuals and is believed to be decreasing.

"Based on current knowledge about this species, it has a very specialised habitat niche and a very small geographic range.

"The establishment of the Allpahuayo-Mishana National Reserve...which includes much of the known range of P. arenarum, was a critical step in the protection of this species.