Phylogenetic-controversy
Guides
Acariformes
Actinotrichida
Acariformes is one of two superorders of mites, representing the more diverse lineage with over 32,000 described species in 351 families and an estimated total of 440,000–929,000 species. Recent phylogenomic analyses indicate Acariformes is the most deeply rooted chelicerate lineage, rendering the traditional grouping of all mites into a single taxon scientifically problematic. The superorder comprises two main clades: Sarcoptiformes (including Oribatida and Astigmatina) and Trombidiformes, with the enigmatic Endeostigmata representing primitive forms of uncertain placement.
Merostomata
Horseshoe Crabs
Merostomata is a class of chelicerate arthropods containing the extinct Eurypterida (sea scorpions) and the extant Xiphosura (horseshoe crabs). The group is characterized by appendages that function as mouthparts proximally and swimming legs distally, reflected in the etymology from Greek μηρός ('thigh') and στόμα ('mouth'). Phylogenetic status remains debated: some analyses suggest Merostomata is not monophyletic, with Xiphosura basal to a clade comprising Eurypterida and Arachnida, while a 2022 analysis recovered monophyly with Xiphosura in a derived position.