Question

Bilateral symmetry is found in
(a) Cnidaria
(b) Platyhelminthes
(c) Mollusca
(d) Both (b) & (c)

Answer 1

Hint: Bilateral symmetry of an organism is the mirror image of the organism along a middle line known as the sagittal plane. The organisms possessing bilateral symmetry have a dorsal side and ventral side with distinctive left and right sides. They also possess anterior side and posterior side. This type of symmetry is advantageous as it permits the organism to be streamlined in shape.

Complete step by step answer:
Bilateral symmetry is found in Platyhelminthes and Mollusca. If we draw a line from the interior and of the organism in Platyhelminthes to the posterior and then it will reflect each other forming bilateral symmetry which creates two matching halves. In molluscs, there is bilateral symmetry but at larval stages, due to torsion, it shows asymmetrical behaviour.

Additional information:
Cnidaria: Cnidaria constitutes almost Marine animals which includes corals, hydras, jellyfishes, sea anemones, etc. Cnidaria is also known as a coelenterate as they have a sac-like body with a single mouth opening. The skeletons of these organisms are calcareous which are used in making the frameworks of reefs and atolls. These organisms are radially symmetrical and lack cephalization.
Platyhelminthes: Platyhelminthes are the invertebrates that are usually flattened and have soft bodies. due to their flattened structure, they are also known as flatworms. Platyhelminthes are bilaterally symmetrical, lack respiratory and circulatory systems. They are coelomates as they have nobody cavity present inside them. They are hermaphrodites and have a head region with sense organs and nervous tissues. The incident of tapeworm infestation of humans in Europe, Australia, and North and South America has been reduced due to routine meat inspection but where sanitization is poor the incident of tapeworm infestation is high. They show the process of regeneration by which they can obtain the whole organism from the piece of itself.
Mollusca: Molluscs are the invertebrates with wholly or partly enclosed calcium carbonate shells with a soft mantle covering the body. Molluscs can live in all habitats except air. They are mostly marine, bivalves, and gastropods including freshwater species. They are found on the rocky, sandy, and muddy areas and can burrow, crawl, and can swim freely.
So, the correct answer is 'both (b) & (c)' .
Note: Tapeworm size can grow up to the size of the school bus. The longest size found it was 90 feet. They lived around 200 million inside humans around the world. Flatworms can stick to the pharynx of their prey and can suck the insides like a vacuum cleaner. Fluke which is an example of Platyhelminthes can produce up to 500,000 embryos.
Molluscs are known for their self-defence. Molluscs have around 80000 of their species alive. Mollusk is the second largest phylum in the animal kingdom. 23% of the Marine population is of molluscs. Most molluscs are vegetarian and consume fungi, algae, and plants. Octopuses and cuttlefishes are some of the advanced molluscs.