the Xiphosura, but since have been assigned to separate classes: Aglaspida Walcott, 1911 (Cambrian to Ordovician) Chasmataspidida Caster & Brooks, 1956 (Lower Ordovician) Cladogram Cladogram after Lasmdell 2020. See also Synziphosurine List of xiphosurans References Further reading B. B. Rohdendorf (ed.) Fundamentals of Paleontology, vol. 9, Arthropoda-Tracheata and Chelicerata: 894 pp. [1991 English translation of Russian original, Smithsonian Institution Libraries and National Science Foundation]. R. E. Snodgrass. 1952. A Textbook of Arthropod Anatomy. Hafner Publishing Company, New York. External links Peripatus - an overview of arthropod relationships. Paleos - a site with a synoptic account of the Xiphosura, focused on fossils. Xiphosura - the article from the UCMP Web Taxa project. Xiphosura Educational Worksheet for Kids on EasyScienceforKids. Chelicerate orders Extant Silurian first appearances Taxa named by Pierre André Latreille