Question

Subkingdom Parazoa includes
A. Protozoa
B. Porifera
C. Metazoa
D. None of the above

Answer 1

They include sponges. They are distinguished by the lack of body organs, nervous tissue, cell division and cellular autonomous specialisation. They lack a true mouth and have unusual collar cells, and their digestion is intracellular.

Complete answer:
- Parazoa is an animal subkingdom that comprises the phyla Porifera and Placozoa. Sponges are the most common parazoa in the world. They are marine animals categorised within the Porifera phylum with about 15,000 species worldwide. Though multicellular, sponges have only a few different types of cells, several of which travel throughout the body to perform various functions. Cells in the sponge walls trap materials out of the water as the water is pumped into the body and into other wider openings.

- Protozoa are microscopic unicellular eukaryotes that have a comparatively complex internal structure and conduct complex metabolic activities. Some protozoa have propulsion mechanisms or other kinds of motion. The Protozoa are regarded to be the subkingdom of the Protista kingdom, although they are placed in the classical system of the Animalia kingdom.

- Metazoan animals are multicellular, mitochondrial eukaryotes. Currently, metazoa includes all animals with distinct tissues, including nerves and muscles. The metazoans evolved from the protists about 700 million years ago.

Thus, the correct answer is B. Porifera.

Note: Placozoans are closely related to poriferans and have been categorised within the Parazoa Subkingdom as an independent phylum. The only remaining Parazoans are the sponges belonging to the phylum Porifera and the Trichoplax of the phylum Placozoa.