Question

An animal having unsegmented coelom, superficial radial symmetry in adult but bilateral symmetry in larva is a member of
A) Mollusca
B) Echinodermata
C) Arthropoda
D) Annelida

Answer 1

Hint:These animals have an endoskeleton and are characterized by their hard, spiny covering. They have a rich fossil history and exhibit a great diversity of body forms, even the extinct ones.

Complete answer:
First, we need to understand what is coelom and symmetry in animals?
i) Symmetry- Animals are classified on the basis of their symmetry as Asymmetrical, radial, and bilateral. ii) Asymmetry -It is when any plane that passes through the center does not divide them into equal halves. For example, in sponges.
When any plane passing through the central axis of the body divides the organism into two identical halves, it is known as radial symmetry. This is found in coelenterates, ctenophores, and echinoderms.
Bilateral symmetry is when the body can be divided into identical halves in only one plane. Example, annelids, arthropods, etc.
The coelom is the body cavity lined by mesoderm. Such animals, with a body cavity, are called coelomates whereas in animals like Platyhelminthes, the body cavity is absent and they are called acoelomates. In some animals, the body cavity is not lined by mesoderm but is present in pouches between the ectoderm and endoderm. Such a body cavity is called pseudocoelom.
An animal with unsegmented coelom, superficial radial symmetry, and bilateral symmetrical larva belongs to Echinodermata. Thus the correct option is option B, ‘Echinodermata’.
Echinoderms are spiny skinned, free swimming, and triploblastic animals. They are marine and benthic i.e. bottom-dwelling animals. They do not show any segmentation in the body and lack a head. The most characteristic feature is the presence of a water vascular system that helps in locomotion, food capture, respiration, and attachment of the body to a substratum. Examples: Asterias (starfish), Antedon, Rhizoctonia, Echinoidea (sea urchin), Holothuroidea (sea cucumbers), etc.

Hence the correct answer is option ‘B’.

Note:The echinoderms are important both ecologically and geologically. Ecologically, they are abundant in the biotic desert of the deep sea, as well as the shallower oceans. Most of them are able to reproduce asexually and regenerate tissue, organs, and limbs. Geologically, their ossified skeletons are valuable. They are major contributors to many limestone formations, and can provide valuable hints as to the geological environment.