[3][4] The species D. australis was first described by the American naturalist James Eights based on specimens found in the sea along the South Shetland Islands in the Antarctic region in 1834.

[3][4] The French zoologist Eugène-Louis Bouvier described one of these sea spiders as a new species, D. antarctica, in 1905, but authorities have since deemed D. antarctica to be a junior synonym of D. australis,[1] Another species in this genus, D. qasimi, was described by V. Jaya Sree, R.A. Sreepada, and A.H. Parulekar of the National Institute of Oceanography in India in 1993.

The original description of this species is based on a male holotype found at a depth of 150 m off the coast of Queen Maud Land in Antarctica.

[6] The molecular evidence also indicates that the polymerous clade including Decolopoda and Dodecolopoda is nested within a monophyletic group containing the "longitarsal" species in the genus Colossendeis.

[6] Sea spiders of the giant species Decolopoda australis are bright scarlet and have five pairs of legs.

Setae cover the entire body of the hirsute variety except for the front half of the trunk and the base of the proboscis.

[3] The polymerous genera Decolopoda and Dodecolopoda both differ from their close relatives in the genus Colessendeis not only by featuring more legs but also by retaining chelifores as adults.

This sea spider, like its close relatives in the genus Dodecolopoda, uses all of its legs in walking with a metachronal rhythm.

This species has been collected from many Antarctic and Subantarctic locations, from the Ross Sea to Heard Island in the Indian Ocean, and at a wide range of depths, from littoral to 1890 m below the surface.