2022, Advent calendar Door 9: Challenging the Historical Perception of Arachnid Monophyly by Håkon Knudsen December 9, 2022 0 The arthropod subphylum of Chelicerata are made up of three classes containing extant orders: Pycnogonida (Pantopoda: the sea spiders), Merostomata (Xiphosura: ... Read more.