Question

An animal phylum is defined on the basis of
A. The uniqueness of its DNA content
B. The uniqueness of its body plan
C. Type of body plan symmetry
D. Fundamental habitat (aquatic terrestrial, etc.)

Answer 1

Hint:- More than a million species of animals that differ in structure and form have been described till now. Besides various features, there are some fundamental features that are common to various individuals with respect to the arrangement of cells, body symmetry, nature of coelom, patterns of various organs-systems, etc.

Complete step-by-step solution:- Body plan can be defined as a group of structural and developmental characteristics that are used to identify a group of animals. The shape and the size of the animals show a great diversity and on these basis, animals have three types of body plan:
- Cell aggregate plan- In this, the body is just an aggregate of cells with no coordination between them and little differentiation, example, sponges.
- Blind sac plan- In this, multicellular animals have tissue or organ-system organization but there is an incomplete alimentary canal in which a single opening acts as both mouth for ingestion and anus for egestion, e.g. flatworms. It is also found in coelenterates.
- Tube within a tube plan- The animals with this plan have organ-system organization and are complete alimentary canal having two separate openings- mouth at the anterior end and anus at the posterior end.
- Protostomous- In this type, blastopore of archenteron of gastrula larva forms mouth and is formed earlier than anus, e.g. in roundworms, annelids, molluscs and arthropods.
- Deuterostomes- In this, the blastopore of gastrula forms anus, so anus is formed earlier than mouth, for example, in echinoderms and chordates.

Note:- Animals are multicellular, heterotrophic eukaryotes. The cells in their body are of several types and are organized into functional units of progressively increasing complexity i.e. tissues, organs and organ-system.