Why are turtle not artropod?

Turtles are vertebrates (phylum Chordata, the chordates) as they have an internal skeleton including a spinal (vertebral) column or backbone. By contrast, phylum Arthropoda (the arthropods) are characterized by exoskeletons made from chitin, segmented bodies, and jointed appendages; along with other differences, they do not have backbones like turtles.