This document discusses the evolutionary relationships between chordates, hemichordates, and echinoderms. It notes that chordates and hemichordates share some characteristics like a dorsal nerve cord and pharyngeal slits, though it is unclear if these are homologous. Chordates are distinguished by features like a tadpole larva, notochord, post-anal tail, and endostyle. The document suggests that hemichordates, chordates, and echinoderms had a common ancestor and that early echinoderms were sessile filter feeders. Through paedomorphosis, chordates evolved from these sessile ancestors into a larval form that was mobile and fish-like,