Q.86 Animals belonging to phylum Echinodermata are closer to chordates than other
invertebrate phyla. Which ONE of the following reasons can account for this relatedness?
(A) Highly evolved nervous system (B) Radially symmetric body plan
(C) Deuterostomic development (D) Well–developed muscles

Echinodermata and Chordates Share Deuterostomic Development, Making Them Closely Related in Evolutionary Terms.

The correct answer is (C) Deuterostomic development, as this shared embryonic pattern groups echinoderms with chordates, distinguishing them from other invertebrates like protostomes.

Option Analysis

Highly Evolved Nervous System (A): Echinoderms possess a decentralized nerve net with radial nerve cords and no brain, which is primitive compared to the centralized dorsal hollow nerve cord in chordates. This feature does not indicate close relatedness and is absent in many invertebrates.

Radially Symmetric Body Plan (B): Adult echinoderms exhibit pentaradial symmetry, while chordates show bilateral symmetry; larvae of echinoderms are bilateral, but radial symmetry aligns echinoderms more with cnidarians than chordates.

Deuterostomic Development (C): Both phyla develop the anus from the blastopore (deuterostomy), with radial indeterminate cleavage and enterocoelous coelom formation, confirming their placement in the deuterostome clade alongside hemichordates.

Well-Developed Muscles (D): Echinoderm muscles are smooth-like and body-wall based, similar in some ways to chordates but not uniquely shared; protostomes also have advanced musculature, so this lacks specificity for relatedness.

Echinodermata closer to chordates than other invertebrate phyla stems from their shared evolutionary lineage in the deuterostome superphylum. This CSIR NET life sciences question highlights deuterostomic development as the key reason, setting echinoderms apart from protostome invertebrates.

Deuterostomic Development Key

Deuterostomes form the anus first from the blastopore, contrasting protostomes where the mouth develops first. Echinoderms and chordates share radial cleavage, enterocoely coelom, and larval similarities, evidenced by molecular phylogenies.

Why Not Other Options?

• Nervous system in echinoderms is a simple nerve ring, not advanced like chordates.

• Radial symmetry is echinoderm-specific in adults, unlike bilateral chordates.

• Muscles exist across phyla without unique shared traits.

CSIR NET Exam Insights

For competitive exams, recognize deuterostomes (Echinodermata, Hemichordata, Chordata) via embryonic traits. This relatedness explains evolutionary links despite adult differences.