Cladogram showing some major events in deuterostome evolution.
Relationships of living organisms are based on molecular data (–); fossils are placed using morphological homologies. 1, Dipleurula-type larva and tripartite organization of body coeloms; 2, Multiplated calcite skeleton with stereom microstructure; 3, Complete ctenidial ring; 4, Periproct non-terminal; 5, Water vascular system with single hydropore (asymmetric development of coeloms); 6, Adult body plan not bilateral (associated with larval attachment and torsion during metamorphosis in extant groups); 7, Tentacular feeding; 8, Radial organization of water vascular system.
Zamora S, Rahman IA, Smith AB (2012) Plated Cambrian Bilaterians Reveal the Earliest Stages of Echinoderm Evolution. PLoS ONE 7(6): e38296. doi:10.1371/journal.pone.0038296