Yes, turtles are indeed part of the phylum Chordata. This phylum includes all animals that have a notochord at some stage in their development. The notochord is a flexible, rod-shaped body that provides support in the embryonic stage. In turtles, as in other vertebrates, the notochord is replaced by the vertebral column (spine) as they develop.
Turtles belong to the class Reptilia within the phylum Chordata. They are characterized by their hard shells, which are made up of a carapace (the upper part) and a plastron (the lower part). This unique feature provides them with protection from predators and environmental hazards.
In summary, turtles are chordates because they possess a notochord during their embryonic development, which later develops into a vertebral column. This places them firmly within the phylum Chordata, alongside other vertebrates such as mammals, birds, fish, and amphibians.