Taxonomy classification schemes change as new evolutionary evidence emerges.
Keep in mind that Hemichordates are now placed between Echinoderms and Chordates, and their characteristic "notochord-like" structure is the stomochord.
Hemichordata is not considered as a chordate sub-phylum, and possesses a proto-notochord called stomochord.
Hemichordata is a sub-phylum under Chordata and possesses a proto-notochord called stomochord.
Hemichordata is a sub-phylum under Chordata and possesses a proper notochord and gill slits like chordates.
Hemichordata is not considered as a chordate sub-phylum because it possesses a water vascular system.
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The Correct Option isA
Solution and Explanation
Step 1: Understanding the Question:
The question asks us to identify the correct taxonomic and anatomical description of the Phylum Hemichordata. Step 2: Key Formula or Approach:
We can evaluate the taxonomic placement and key characteristics of Hemichordates based on animal classification:
1. Hemichordates were previously classified as a sub-phylum under Phylum Chordata due to a buccal diverticulum once mistaken for a notochord.
2. Today, they are placed as a separate independent phylum under Non-Chordata (Invertebrates).
3. They possess a rudimentary structure in the collar region called the stomochord (buccal diverticulum), which is structurally different from a true chordate notochord. Step 3: Detailed Explanation:
Let's analyze the statements one by one:
- Option (A): "Hemichordata is not considered as a chordate sub-phylum, and possesses a proto-notochord called stomochord."
- This statement is correct. Hemichordata is now treated as a separate phylum of non-chordates.
- The structure once thought to be a primitive notochord is now known as a stomochord.
- Option (B) and (C): These are incorrect because Hemichordata is no longer considered a sub-phylum under Chordata, nor does it possess a true/proper notochord.
- Option (D): This is incorrect because the water vascular system is a unique diagnostic feature of Phylum Echinodermata, not Hemichordata. Hemichordates do not possess a water vascular system. Step 4: Final Answer:
Thus, option (A) is the only accurate statement.
