Question

Second largest phylum of animal kingdom is
A. Arthropoda
B. Protozoa
C. Mollusca
D. Pisces

Answer 1

Hint: Phylum is the primary subdivision of the taxonomic kingdom. There are a total five kingdoms out of which animalia kingdom is the largest. The animalia kingdom has 10 distinct phylums.

Complete answer:
Phylum is the primary subdivision of the taxonomic kingdom. All the members of animalia are multicellular and exhibit different patterns of cellular organization. There are 10 distinct phylum in animal kingdom, and they are porifera, Coelenterata, Ctenophora, Platyhelminthes, Aschelminthes, Annelida, Arthropoda, Mollusca, Echinodermata, Hemichordate, Chordata.
The largest animal kingdom is Arthropoda and Mollusca comes second.
Mollusks have soft bodies. They are bilaterally symmetrical, segmented, and coelomates (have body cavity called coelom). They are shelled having a mantle, ventral foot, anterior head, and a dorsal visceral mass.
They are aquatic animals, either freshwater or terrestrial. They are very much different in size, they vary from a giant squid to small snail. They are triploblastic (have three embryonic cell layers: ectoderm, mesoderm, endoderm).
They have soft, unsegmented bodies except in Monoplacophora. They are bilaterally symmetrical (a form of symmetry where both sides are equal). They have a tissue grade system of organization.
They are dioecious (separate sexes). Fertilization is external or internal. Development is direct or through metamorphosis.
They respire directly or by gills or lungs or both. Excretion is carried out by metanephridia. They have a simple digestive tract with anterior mouth and posterior anus. Their circulatory system is open.
Examples: Gastropods, Octopus, Chitons

Thus, from the above discussion it is clear that the correct answer is option ‘C’- Mollusca.

Note: The most commonly followed kingdom system was given by Robert H. Whittaker in 1969. He built it on the previous studies of Linnaeus. The kingdoms are Monera, Protista, Fungi, Plantae, Animalia. It is the most followed way of grouping things based on simple living characteristics.