What defining structural feature necessitates placement in Phylum Chordata for the White Catfish?
Presence of a notochord at some stage of development
The Phylum Chordata groups together animals that share a fundamental developmental characteristic, irrespective of what that structure develops into later in life. The essential unifying feature is the presence, at some point during the organism's life cycle—be it embryonic or adult stages—of a flexible, rod-like structure known as the notochord. This structure provides primary skeletal support. While the White Catfish, as a bony fish classified in the Class Actinopterygii, ultimately develops a full backbone (spinal column) replacing the embryonic notochord, the initial presence of the notochord places it squarely within the Chordata phylum. This places it in the lineage of animals possessing a backbone or spinal cord, distinguishing it from invertebrate phyla.
