Radial symmetry is NOT found in adults of phylum ______. (NEET 2023)a)Ctenophorab)Hemichordatac)Coelenteratad)EchinodermataCorrect answer is option 'B'. Can you explain this answer?

Question

Radial symmetry is NOT found in adults of phylum ______.   (NEET 2023)a)Ctenophorab)Hemichordatac)Coelenteratad)EchinodermataCorrect answer is option 'B'. Can you explain this answer?

Answer

Radial symmetry is a type of symmetry where an organism can be divided into similar halves by more than two planes passing through the central axis. This type of symmetry is found in organisms that tend to meet their environment in all directions, such as aquatic animals.

Hemichordata : Adult organisms in this phylum, which includes acorn worms, pterobranchs, and graptolites, exhibit bilateral symmetry. This means they can be divided into two identical halves only along a single plane. Hence, radial symmetry is not found in the adults of this phylum.
Coelenterata (also known as Cnidaria) : This phylum includes jellyfish, sea anemones, and corals. They exhibit radial symmetry. So, radial symmetry is found in this phylum.
Echinodermata : Adult organisms in this phylum, which includes starfish, sea urchins, and sea cucumbers, exhibit radial symmetry. However, it's important to note that their larvae exhibit bilateral symmetry. Therefore, radial symmetry is found in adults of this phylum.
Ctenophora (also known as comb jellies) : These marine animals also exhibit radial symmetry. Thus, radial symmetry is found in this phylum.

Answer

Understanding Radial Symmetry
Radial symmetry is a body plan in which body parts are arranged around a central axis. This type of symmetry is most commonly found in organisms that are aquatic and often sessile or free-floating.
Phylum Analysis
- Ctenophora (Comb Jellies):
- Exhibit radial symmetry in adults.
- Hemichordata (Acorn Worms):
- Adults display bilateral symmetry, not radial.
- They possess a segmented body and a distinct head region.
- Coelenterata (Cnidaria):
- Have radial symmetry in their adult forms (e.g., jellyfish, corals).
- Echinodermata (Starfish, Sea Urchins):
- Exhibit radial symmetry, typically pentamerous (five-part) symmetry in adults.
Conclusion
The correct answer is B (Hemichordata) because, unlike the other phyla listed, hemichordates demonstrate a bilateral symmetry as adults. Understanding these symmetries helps in the classification and study of various organisms within their respective phyla.

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