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Taxonomists have classified certain animals into two groups based on their skeletal support: Group A includes all animals that possess a notochord at some stage of their life cycle. Group B includes animals that possess a cartilaginous or bony vertebral column. It is observed that all members of Group B belong to Group A, but the reverse is not true. Which of the following developmental events correctly explains this

Options

  1. AThe vertebral column in Group B is formed by the calcification of the dorsal hollow nerve cord.
  2. BOrganisms in Group B possess both a notochord and a vertebral column simultaneously throughout their adult lif
  3. COrganisms in Group B possess a notochord during their embryonic period, which is replaced by a vertebral colum
  4. DOrganisms in Group A lose their notochord during embryonic development before forming a vertebral column.

Correct answer

C. Organisms in Group B possess a notochord during their embryonic period, which is replaced by a vertebral colum

Step-by-step solution

Group A represents the Phylum Chordata, while Group B represents the Subphylum Vertebrata. Members of Vertebrata possess a notochord during the embryonic period. This notochord is later replaced by a cartilaginous or bony vertebral column in the adult stage. Because they have a notochord at some stage of their life cycle, they are included in Group A (Chordata). However, protochordates (such as Urochordata and Cephalochordata) belong to Group A but never develop a vertebral column, which is why the reverse is not t

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