Polyascus is a genus of barnacles in infraclass Rhizocephala.

It was circumscribed in 2003 by Henrik Glenner, Jørgen Lützen, and Tohru Takahashi.

The generic name polyascus (poly "many" + ascus "bag") refers to the typical presence of multiple external sac-like female bodies, known as externae.

In Polyascus species, these originate from asexual reproduction.

[1] As of 2017[update], WoRMS recognizes the following three species, all included in the genus's circumscription.