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Question

It is believed that true chordates have evolved from the phylum ___.


  1. Echinodermata

  2. Hemichordata

  3. Cephalochordata

  4. Urochordata


Solution

The correct option is B

Hemichordata


True chordates are those that exhibit the primary chordate characteristics: notochord, dorsal hollow nerve cord and paired pharyngeal gill slits. It is believed that these animals evolved from the hemichordates (such as the acorn worm), which exhibit certain chordate-like characteristics. There are branchial openings, or "gill slits," that open into the pharynx; there is a rudimentary structure in the collar region, the stomochord, that is similar to a notochord; and there is a dorsal nerve cord, in addition to a smaller ventral nerve cord. However, hemichordates are not classified as true chordates, although they are quite closely related. Urochordates are the first group of true chordates, followed by the cephalochordates and vertebrates.

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