Which one of the following statements is correct?

• A

  Hemichordata is not considered as a chordate sub-phylum because it possesses a water vascular system.
• B

  Hemichordata is a sub-phylum under Chordata and possesses a proto-notochord called stomochord.
• C

  Hemichordata is a sub-phylum under Chordata and possesses a proper notochord and gill slits like chordates.
• Correct answer
  D

  Hemichordata is not considered as a chordate sub-phylum, and possesses a proto-notochord called stomochord.

Hence, the correct answer is option: 'D'.