What fundamental structure must an animal possess at some life stage to be classified under Phylum Chordata?
Answer
A notochord
The classification of weasels into the Phylum Chordata is based on meeting specific developmental criteria that are present at some point during their lifecycle. The most foundational of these structures is the notochord, a flexible rod providing skeletal support. Other defining chordate features include a dorsal hollow nerve cord, which develops into the central nervous system; pharyngeal slits; and a post-anal tail. The presence of these features, even if modified or reduced in adulthood, confirms their placement within this phylum, separating them from invertebrates like mollusks or arthropods.
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