Weissius capaciductus is a species of dugesiid triclad found in Australia.

It is the only species in the monotypic genus Weissius.

[1] The genus was named for Annie Weiss, a planarian worker, in honor of her contributions to knowledge of Australian freshwater planarians.

The specific epithet is derived from Latin, meaning "spacious duct" (capax + ductus), in reference to the expanded anterior section of the species' oviducts.

The base color is light with speckled darker brown pigment, concentrated around the pharynx.