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All chordates possess the following features except
A. Dorsal hollow nerve cord
B. Pharyngeal gill slits
C. Notochord
D. Amnion

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Last updated date: 13th Jun 2024
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Answer
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Hint:- A chordate is an animal belonging to the phylum Chordata. Chordates are among the most developed phylum and are bilaterally symmetric and consist of a coelom, metameric segmentation, and closed circulatory system, digestive and excretory system.

Complete answer:
The characteristic features include the presence of a notochord, a dorsal hollow nerve cord, paired pharyngeal gill slits, a post-anal tail, and the presence of an endostyle or thyroid gland. The notochord is a rod-like structure. The notochord lies along the anteroposterior axis of the body and is derived from the mesodermal cells. The functions of the notochord are it serves as a midline tissue that provides directional signals to surrounding tissue during development and as a site of muscle attachment, and vertebral precursor.
Pharyngeal slits are filter-feeding organs found in Invertebrate and some chordates (lancelets and tunicates) and hemichordates which live in the aquatic environment. The dorsal hollow nerve cord is formed from a part of the ectoderm that rolls, forming the hollow tube. In vertebrates, the dorsal nerve cord is further developed into the central nervous system, which consists of the brain and spinal cord. It is one embryonic feature unique to all chordates, among the other four chordate features.
Amnion is one of the four extraembryonic membranes or foetal membranes i.e amnion, chorion, allantois, and yolk sac. The space between the amniotic membrane and embryo is filled with amniotic fluid which helps in the prevention of the desiccation of the embryo by providing the embryo with a water-retaining environment and proper nutrition.
Thus, the right option is D.

Note:- Phylum Chordata consists of three subphylums as follows -
● Urochordata
● Cephalochordata
● Vertebrata
Amnion is present only in mammals, birds, and reptiles of vertebrae. It is the innermost layer that encloses the embryo. It is not present in all the chordates like Urochordates and Cephalochordates.