530 million years ago to 440 million years ago, later invertebrates {higher invertebrate} had ganglia, separate mouth and anus, muscular guts, developed circulatory systems, and coeloms. Chordates split from roundish flatworms 530 million years ago. For example, arthropods have nervous system on front, and vertebrates have nervous system on back. Both animal groups use same two genes for front and back, but chordate dorsal side is homologous with arthropod ventral side.
Biological Sciences>Zoology>Kinds>Invertebrate
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Date Modified: 2022.0224