Q.87 Which one of the following is characteristic of deuterostomes?
(A) Radially symmetric body
(B) Bilaterally symmetric body
(C) Presence of well-defined digestive system
(D) Formation of anus from blastopore
Deuterostomes are characterized by the formation of the anus from the blastopore during embryonic development. This defining feature distinguishes them from protostomes, where the blastopore becomes the mouth.
Options Explained
Radially Symmetric Body (A)
Radial symmetry occurs in some deuterostomes like echinoderms (adults), but not chordates (e.g., humans exhibit bilateral symmetry). This trait is not universal or defining for the group.
Bilaterally Symmetric Body (B)
Bilateral symmetry is common in deuterostome larvae and chordates but absent in adult echinoderms, making it non-specific. Many protostomes also show bilateral symmetry.
Presence of Well-Defined Digestive System (C)
A complete digestive system exists in most animals, including both protostomes and deuterostomes. This is a general metazoan feature, not unique to deuterostomes.
Formation of Anus from Blastopore (D)
This is the hallmark deuterostome trait: the blastopore (first embryonic opening) forms the anus, with the mouth arising secondarily. Protostomes show the reverse (blastopore → mouth).
Deuterostome characteristic of anus formation from blastopore sets them apart in animal development, crucial for NEET aspirants studying embryology.
Deuterostome vs Protostome Key Differences
Deuterostomes (echinoderms, chordates) show radial cleavage, indeterminate development, enterocoely coelom, and blastopore → anus. Protostomes exhibit spiral cleavage, determinate fate, schizocoely, and blastopore → mouth.
| Feature | Deuterostomes | Protostomes |
|---|---|---|
| Blastopore Fate | Anus | Mouth |
| Cleavage | Radial, indeterminate | Spiral, determinate |
| Coelom Formation | Enterocoely | Schizocoely |
| Examples | Humans, starfish | Arthropods, mollusks |
Embryonic Development Insight
During gastrulation, deuterostome blastopore invaginates to form the anus; a secondary opening becomes the mouth. This “deutero” (second) mouth naming reflects the pattern.
Why Option (D) is Correct
Standard biology texts confirm blastopore fate as the primary deuterostome diagnostic, with consistent evidence across phyla like Chordata and Echinodermata.
