Question

The second largest number of species containing phylum in the animal kingdom is-
a. Annelida
b. Arthropoda
c. Mollusca
d. Chordata

Answer 1

Hint: The second largest number of species containing phylum in the animal kingdom contains about two hundred thousand types of species worldwide, of which approximately eighty-five thousand are being identified. They are the second largest phyla after arthropoda, which contains about eighty four percent of all known species of animals. They have a hard calcareous layer on their body. The organism of this phylum is also used as an ornamental purpose by humans.

Complete answer:
> The phylum mollusca have the second largest number of species after the phylum Arthropoda. Molluscs are the largest marine phylum and they comprise about twenty percent of all the identified marine organisms in them. They are among the most diverse organisms of earth. The phylum Mollusca generally contains organisms like snails, squids, clams, oysters, octopuses etc in them. Hence, the option (c) Mollusca is the correct answer.

> The option (a) Annelida is among the third largest species of animal kingdom, which shows diversity. The body of Annelids is segmented and they respire through their body surface. The excretory organs present in them are nephridia. They have a properly developed circulatory and digestive system.

> The option (b) Arthropoda has the largest number of species in the animal kingdom. They contain eighty percent of the entire species on earth. They have a segmented body which is differentiated into a head, a thorax, and abdomen segments. They have a hard exoskeleton structure, made up of chitin, which help in providing physical protection and resistance.

> Option (d) Chordata is also a diverse phylum of animal kingdom. They contain about sixty thousand of species in them. The members of this phylum are characterized by the presence of a notochord, a dorsal hollow nerve cord and paired pharyngeal gill slits.

Hence, the option (c) Mollusca is the correct answer.

Additional information:
The organisms belonging to this phylum are both marine and freshwater organisms. They have a body cavity and the body is divided into head, visceral mass, a muscular foot and a mantle. Their heads are composed of tentacles and compound eyes. The body is covered with a calcareous shell. They have an important role in the lives of humans, as they are a source of jewelry and also a source of food. The natural pearls that are worn as an ornament are obtained within them.

Note: The molluscs are the highly diverse phylum. They not only show various anatomical structures and sizes, but also have diversity in behavior and habitat. The mollusks are an important part of ecological communities and also a part of every ecosystem of the world. They are found from mountain tops to the hot vents and into the cold deep sea. They can be of size from twenty-meter-long giant squid to a tiny or microscopic aplacophora.