Answer: The presence of a true notochord in Balanoglossus is doubtful, so Hemichordata is now a separate phylum.
- A It lacks bilateral symmetry, instead showing radial symmetry typical of cnidarians under most conditions encountered
- B The presence of a true notochord in Balanoglossus is doubtful, so Hemichordata is now a separate phylum
- C It possesses a closed circulatory system, unlike the open system found in true chordates as commonly observed in practice
- D It develops without a coelomic body cavity during embryogenesis in many documented cases according to conventional understanding
Correct answer: B. The presence of a true notochord in Balanoglossus is doubtful, so Hemichordata is now a separate phylum
Explanation: Balanoglossus (Hemichordata) was earlier placed under Chordata, but since the structure resembling a notochord is not considered a true notochord, Hemichordata is now classified as a distinct phylum separate from Chordata.
Moving across the animal phyla, body organisation becomes progressively more complex: from no symmetry and cellular organisation (Porifera) through radial/diploblastic (Cnidaria), bilateral/acoelomate (Platyhelminthes), pseudocoelomate (Nematoda), to a true coelom with full organ systems (Annelida and beyond).
Concept context
Phylum-level classification of the animal kingdom from Porifera to Chordata, based on body symmetry, coelom, and segmentation. One of the most example-heavy chapters for NEET.