Question

Star fish is a marine echinoderm. What is the symmetry seen in the larva and adult stages?
A. Pentameric radial symmetry is seen in larva and bilateral symmetry in adults.
B. Bilateral symmetry is seen in larva and pentameric radial symmetry in adults.
C. Pentameric radial symmetry is seen in both larva and adult stages.
D. Bilateral symmetry is seen in both larva and adult stages.

Answer 1

Hint: Echinoderms are marine animals which have either a star shaped or spherical or cylindrical body shape. The development of the organisms of these phyla is indirect through a larva. Both the echinoderm larva and the adult have a characteristic symmetry in their body structure. Star fish are marine and bottom dwelling (benthonic) animals found in the littoral zone of the sea. They have pentamerous arms emanating from a central pentagonal disc of the body.

Complete answer:
Option A: In this option the larva is said to have a pentameric radial symmetry which is not true.
Therefore, this option is incorrect.
Option B: In this option the larva is said to have a bilateral symmetry while the adult has a pentameric radial symmetry which is correct.
Thus, this option is correct.
Option C: This option says that both the larva and the adult have pentameric symmetry which Is not correct as the larval forms of starfish are not radially symmetrical.
So, this option is incorrect.
Option D: This option is also not correct because the adult star fishes have radial symmetry instead of bilateral symmetry.
Hence, this option is also not correct.

Hence, Option B is the correct answer.

Note:
An animal is symmetrical only when a plane passes through the center of the animal divides it into two similar halves; if the animal cannot be divided into two halves, it is considered asymmetric. The symmetry of organisms is basically of four types namely, spherical, radial, bilateral or biradial. The structural organization of an organism defines its symmetry.