Although all species in this genus are eight-legged,
phylogenetic analysis based on molecular data indicates that this genus is
paraphyletic with respect to the ten-legged genus
Decolopoda and the twelve-legged genus
Dodecolopoda; these two polymerous (extra-legged) genera are nested within the genus
Colossendeis in a
phylogenetic tree. This paraphyly would normally make both
Dodecolopoda and
Colossendeis junior synonyms of
Decolopoda, the oldest name, and require all three genera to merge under the name
Decolopoda. To avoid this disruption, authorities keep these genera under different names and retain
Colossendeis as a paraphyletic genus. The molecular evidence also indicates that both
Decolopoda and
Dodecolopoda are nested within a
monophyletic group containing the "longitarsal" species in the genus
Colossendeis. The sea spiders in this "longitarsal"
clade feature legs in which the three most distal articles (claw, propodus, and tarsus) taken together are at least three-quarters the length of the fourth most distal article (second tibia). This clade includes not only
Antarctic species of
Colossendeis such as
C. australis and
C. glacialis but also widespread taxa such as
C. megalonyx and
C. robusta. In "brevitarsal" species, such as
C. macerrima, the three most distal articles are instead much shorter relative to the second tibia. ==Species==