The L'Huraxi is one of many, many, MANY xenos species that are briefly mentioned in 40k's fluff and promptly ignored afterwards. L'Huraxites are apparently humanoid giants with purple skins, and are at least capable of at least developing a certain degree of engineering, as their use of massive attack vehicles proves. They fought against the Catachan Jungle Fighters led by Straken at the Battle of Moden's Ridge, though the result of that fight are inconclusive (as in, the text is in the 3rd Ed. Catachan Codex, which is coincidentally the only mention of the L'Huraxi, but I can't find the actual text anywhere, if someone can find it please add it here).

Basically, imagine an army of Thanos riding tanks and fighting Catachan. It would be awesome if we actually had more info than that.

Notable Species of Warhammer 40,000
Major: Eldar, including Dark Eldar Humans, including Abhumans Necrons Orks Tau Tyranids
Minor: Ambull Araklionid Barghesi Banelings Bale Childers Drahendra Caradochians Cimmeriac
Cryptos Cythor Fiends Demiurg Donarathi Drugh Dracoliths Drax Enoulian
Enslavers Fra'al Galg Gykon Hrud Jokaero Jorgall K'nib
Kathaps Khrave Kinebrach Kroot L'Huraxi Lacrymole Laer Lelith
Loxatl Medusae Megarachnids Nekulli Nicassar Old Ones Q'Orl Rak'gol
Rangda Reek Reptos Saharduin Saruthi Scythian Simulacra Slann
Slaugth Sslyth Stryxis Tarellian Thexian Thraxian Thyrrus Tushepta
Umbra Ur-Ghul Vespid Watchers in the Dark Whishperers Xenarch Yu'Vath Zoats