Why is the Amphioxus considered a degenerated chordate?

1. Protonephridia are present in the amphioxus excretory system, which is why it is also known as the degraded Chordata. 
2. The amphioxus lacks a heart, kidney, head, and braid box as well. 
3. The amphioxus has paired limbs, a distinct head, distinct paired sensory organs, and no gonoducts for the gonads. 
4. The segmented kidneys, which are considerably different from those of vertebrates in that they include protonephridia instead of nephrons, make up the excretory system. 
5. Additionally unlike segmented gonads and vertebrates. The marine chordate known as the amphioxus, sometimes known as the lancelet, resembles a fish. 
6. Contrary to vertebrates, a simpler notochord is formed of a cylinder of cells that are tightly packed to produce a hardened covering that protects the dorsal nerve cord instead of a bone.

Hence, option D is the correct answer.