In older zoological classification, a group or phylum designation for animals without a notochord or spinal cord.
From Greek 'a-' (without) + 'chordata' (possessing a cord), an antiquated taxonomic term from pre-molecular biology classification systems.
This term is rarely used now because it was based on absence rather than shared evolutionary history—modern phylogenetics shows that 'achordata' doesn't represent a true evolutionary group, just everything that isn't a chordate!
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