Annabeth. Skeleton – Skeletons are the undead troops that make up Hades' undead army. In The Lightning Thief, Hades has skeletons in army uniforms guarding his palace. In The Battle of the Labyrinth, Nico manages to employ them as part of a ritual that will enable him to call the spirit of his sister to speak with her. In The Last Olympian, Nico and Hades manage to bring a troop of skeletons to help fight the Titans. They are later seen constructing a cabin at Camp Half-Blood which is dedicated to Hades. In The House of Hades, they are on the demigods side and help them in Hades's temple in Epirus. Skolopendra – A sea monster that is 200 ft. long. It looks like a cross between a giant shrimp and a cockroach with a pink chitinous shell, a flat crayfish tail and millipede-type legs. Its face is a slimpy pink like an enormous catfish with two glassy eyes and a gaping toothless maw. In The Mark of Athena, Ceto sent Skolopendra after the demigods after their escape from Phorcys' aquarium. It attacked the Argo II when Leo forgot to turn the monster-detection system on. Skolopendra withdraws into the ocean when Leo Valdez and Hazel Levesque throw test tubes filled with Greek Fire into its mouth. Spartus – A troop of skeletons armed with weapons. They are usually summoned by planting dragon (Sybaris) teeth in the ground and watering them with blood. In The Titan's Curse, some Spartoi ambushed Percy, Thalia, Zoe, Grover and Bianca in New Mexico. Due to her being a child of Hades, Bianca managed to destroy them. In The Son of Neptune, Frank (as a gift from his father) is given a spear with the tip of a dragon's tooth that when planted with raise one of the Spartoi, he uses this to defeat the basilisks outside of the R.O.F.L. headquarters, to kill some of the laistrygonians surrounding his grandmother's house then using his final charge to protect the mortals on a train from attacking Griffins. Gray – A Spartus that can be summoned by Frank Zhang. He lost this ability after his spear ran out of charges. Sphinx – A monster with the head of a woman and the body of a lion. Percy Jackson and his friends encountered the Sphinx while navigating the labyrinth. Rather than tell riddles, the Sphinx asked historical questions which