Question

Why is the Amphioxus considered a degenerated chordate?
A. Due to absence of kidney
B. Due to absence of head
C. Due to absence of brain box
D. All of the above

Answer 1

Hint: The phylum Chordata comprises the cephalochordates means the amphioxus or the lancelets, the urochordates, and the vertebrates. The amphioxus is the highly degenerate vertebrate that lost its skeleton and the complex cranial region.

Complete answer:
The excretory system of amphioxus contains the protonephridia and hence it is also called as the degenerated chordata. The heart, kidney, head and also the braid box are absent in the amphioxus. The paired limbs, distinct head, also distinct paired sense organs are seen in the amphioxus and also the gonads are without gonoducts.

Therefore, the correct answer is option D.

Additional information:
The respiratory system is absent in the amphioxus; they breathe solely through their skin which consists of a simple epithelium. Despite their name little if any respiration occurs in the gill slits, which are solely devoted to feeding. The circulatory system resembles the primitive fish in its general layout, but is much simpler, and does not include the heart. There are no blood cells, and no hemoglobin present.
The excretory system consists of the segmented kidneys containing protonephridia instead of the nephrons, and quite unlike those of the vertebrates. Also unlike vertebrates and segmented gonads.
The amphioxus, also called the lancelet, is a fish-like marine chordate. On contrary to the vertebrates, the dorsal nerve cord is not protected by the bone but by a simpler notochord made up of a cylinder of cells that are closely packed to form a toughened rod in them

Note:
The cephalochordates, commonly called the amphioxus, are the marine invertebrate chordates. They were traditionally held as the closest living relatives of the vertebrates and have long occupied a key phylogenetic position in our discussions on the origin of the vertebrates.