Trichospores ovoid, small (<16 µm long), with a basal collar 1/3-1/2 as long as the spore body, one appendage, Zygospores biconical, but noticeably swollen in the middle, small (<36 µm long), with an oblique collar located at the edge of the medial swelling and one appendage. Thalli branched. In hindgut of larval Chironomidae.

Trichosporae ovales, parvae (< 16 µm longae), collari basali longitudine tertia vel dimidia pars sporae corporis, appendice singulari. Zgyosporae biconicae, medio autem insigniter tumido, parvae (<36 µm longae), collari obliquo ad marginem tumentiae mediae apposito, appendage singulari. Thalli ramosi. In proctodaeo Chironomidarium larvarum.

Austrosmittium shares several features with the common and widespread genus Smittium: trichospores with a collar and single appendage; and zygospores borne obliquely to the zygosporophore (Type II (Moss et al. 1975)). Zygospores, upon release, have a collar and a single appendage, Austrosmittium zygospores differ in having an almost spherical bulge in the middle, and this distinguishes them from the essentially biconical zygospores of all other genera of Harpellales. The small, ovoid trichospores with a long collar are also distinguishing features in both species of Austrosmittium described below. The dimorphic species Smittium orthocladii Manier emend. Lichtwardt (1984) occasionally produces a similar type of small, ovoid spore, but more commonly the trichospores of that species are considerably larger and long-ellipsoidal.

SPECIES TYPICA: Austrosmittium kiwiorum Williams & Lichtwardt.