Which of the following statements about deuterostomes is false?
A All deuterostomes have a similar pattern of early embryonic development.
B All deuterostomes are triploblastic and have three tissue layers.
C All deuterostomes have a coelom.
D All deuterostomes exhibit radial symmetry in their bodies.
The correct answer and explanation is:
Correct Answer: D. All deuterostomes exhibit radial symmetry in their bodies.
This statement is false.
Explanation (300 words):
Deuterostomes are a major group of animals that include echinoderms (such as sea stars and sea urchins), chordates (which include all vertebrates), and hemichordates (like acorn worms). They are united by key developmental characteristics during early embryogenesis.
A. All deuterostomes have a similar pattern of early embryonic development.
True – Deuterostomes exhibit radial, indeterminate cleavage, and during gastrulation, the blastopore becomes the anus (the mouth forms secondarily). This is the hallmark of deuterostomic development.
B. All deuterostomes are triploblastic and have three tissue layers.
True – All deuterostomes are triploblastic, meaning their embryos form three germ layers: ectoderm, mesoderm, and endoderm. This enables them to develop complex tissues and organs.
C. All deuterostomes have a coelom.
True – Deuterostomes are coelomates, meaning they possess a true coelom, a fluid-filled body cavity completely lined with mesoderm. This feature supports organ development and complexity.
D. All deuterostomes exhibit radial symmetry in their bodies.
False – This is the incorrect statement. While radial symmetry is found in adult echinoderms (like sea stars), it is not a universal feature of all deuterostomes. For instance, chordates, which include humans, exhibit bilateral symmetry, especially in their embryonic and adult forms. Even echinoderms start life as bilaterally symmetric larvae and later develop radial symmetry as adults.
Thus, while radial symmetry can be observed in some deuterostomes, it is not a defining characteristic for the entire group. The presence of bilateral symmetry in chordates disproves the statement.
Summary:
Option D is false because not all deuterostomes exhibit radial symmetry—only some, like adult echinoderms, do. Most, including humans, are bilaterally symmetrical.