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Question

Choose the correct combination of features of phylum Annelida:


Your Answer
A
Radially symmetrical, tissue level of organisation, diploblastic
Correct Answer
B
Bilaterally symmetrical, metameric segmentation, true coelom
Your Answer
C
Bilaterally symmetrical, round cross section, pseudocoelomates
Your Answer
D
Bilaterally symmetrical, flatworms, acoelomates

Solution

The correct option is A Bilaterally symmetrical, metameric segmentation, true coelom
Organisms in phylum Annelida have three germ layers, i.e., ectoderm, mesoderm, and endoderm and are hence triploblastic. They also have a true coelom as it is lined by the mesoderm. They have a unique feature known as metameric segmentation. Metamerism is the phenomenon of having a linear series of body segments fundamentally similar in structure. Annelids can be divided into two equal halves in only one plane and, hence, are bilaterally symmetrical.


Organisms having radial symmetry, i.e., when any plane passing through the central axis of the body, divides the organism into two identical halves, tissue level of organisation and two germ layers (ectoderm and endoderm) are seen in phylum Cnidaria and Ctenophora.

Organisms in phylum Aschelminthes are bilaterally symmetrical with a round cross section. They are triploblastic but their body cavity is not lined by mesoderm completely and, hence, are called pseudocoelomates.

Organisms in phylum Platyhelminthes and onwards have bilateral symmetry. They are dorsoventrally flattened and, hence, are called flatworms. They are acoelomates as they don’t have a body cavity at all.
 

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