The Harpellales are an order of fungi classified in the subdivision Kickxellomycotina.

Thalli are either unbranched or branched, producing basipetal series of trichospores.

Species in the order are found attached to the gut lining of aquatic larvae of Insecta or (rarely) Isopoda.

[3] Harpellales has served as a model to study and understand the evolution, growth, and biodiversity of other such fungi found in the gut as species are plentiful around the world.

[4] Species include Allantomyces zopilotei, Bojamyces olmecensis, Gauthieromyces viviparus and Graminella ophiuroidea.