Mollisonia is an extinct genus of Cambrian marine arthropod. Four species have been described from North America and China. Studies suggest it is a basal member of Chelicerata, a group which includes horseshoe crabs and arachnids. From Wikipedia
Neural mapping of a 500-million-year-old Mollisonia specimen reveals the back-to-front brain layout of modern spiders, prompting a reassessment of when arachnids first evolved
