Test: Animal Kingdom- Basis of Classification (April 13) - NEET MCQ

(A) Cellular level
(B) Radial symmetry
(C) Bilateral symmetry
(D) Pseudocoelomates
(E) Coelomates

The animals in which the coelom is absent are called acoelomates, for example flatworms (Planaria). In them the space between ectoderm and endodorm is filled with parenchyma derived from mesoderm.

(i) Diploblastic animals have two germinal layers (ectoderm and endoderm) during embryonic development
Example: Poriferans.
(ii) Triploblastic animals have three germinal layers (ectoderm, mesoderm and endoderm) during embryonic development
Example: Platyhelminthes.

• Animals that belong to the phylum Platyhelminthes to Chordata are all triploblastic.
• But Platyhelminthes and aschelminthes belong to pseudocoelomates.
• Annelids, arthropods, echinoderms and chordates are under eucoelomates. This means not all triploblastic animals are eucoelomates. 
• Pseudocoelomates have false coelom while eucoelomate animals only have the true coelom. 

Hence, both statement 1 and statement 2 are incorrect. 

Coelenterates have radial symmetry. Aschelminth are pseudocoelomates. Molluscs do not show metamerit Sponges are diploblastic.

Bilateral symmetry is defined as the symmetry in which animals can be divided into two halves in one plane only, and these halves are identical to each other. The organisms have paired body organisms that occur on both sides of the body; if this will not happen then the symmetry will no longer remain. This type of symmetry is found in all vertebrates and few invertebrates. Some invertebrates also show radial symmetry, for example, animals belonging to coelenterates, ctenophores and echinoderms. These organisms can be divided into two identical haves through any plane passing through the central axis. So, the incorrect statement regarding bilateral symmetry is option C.

Platyhelminthes are triploblastic, acoelomate organism showing bilateral symmetry. Ctenophores have borads symmetry, are acoelomates having diploblastic organisation. In echinoderms, larvae have bilateral symmetry whiled add have radial symmetry. They are coelomates with triplobla organisation. Annelids are triploblastic, coelomaterorganism showing bilateral symmetry.

Figure 'A' is of coelomates (Annelids), Figure 'B' is a pseudo-coelomates (Aschelminthes) and Figure 'C' is a acoelomates (Plathyhelminthes).

(i) Diploblastic - Poriferans, Coelenterates

(ii) Triploblastic - Platyhelminthes to Chordates

(iii) Acoelomate - Poriferans, Coelenterates, Platyhelminthes

(iv) Pseudocoelomate - Aschelminthes/Roundworms

(v) Eucoelomate - Annelids to Chordates

So, the correct answer is '(i), (ii), (iii), (iv) and (v)'.

A - Ectoderm
B - Endoderm
C - Mesoglea
D - Mesoderm
So, the correct answer is 'A - Ectoderm, B - Endoderm, C - Mesoglea, D - Mesoderm'.