Question

Which of the following is not an aquatic animal?
A. Hydra
B. Jellyfish
C. Coral
D. Roundworm

Answer 1

Different organisms live in a variety of habitats and environment. In due course the organism has evolved several types of adaptation to survive well in that particular environment. Organisms such as bacteria are habituated to various extreme conditions while other organisms cannot tolerate different environments.

Complete answer:
The aquatic organism is the organism that lives in the water for all or most part of their lifetime. Both the invertebrates as well as the vertebrates live their life as aquatic organisms. The aquatic organism bears certain types of adaptation that allows them to survive in the conditions such as breathing or utilizing the oxygen dissolved in water for breathing. They develop specialized organs known as gills or breathe directly through skin.
Hydra belongs to the class hydrozoa of phylum cnidaria which is a genus of small freshwater organisms. They are typically aquatic organisms. It has a tubular radially symmetric body and contains an adhesive foot known as the basal disc. The mouth is present at the free end which is surrounded by one to twelve mobile tentacles. It is a diploblastic animal. The outer layer is known as epidermis and the internal layer is known as gastrodermis. It completes its life cycle in aquatic condition
Jelly fish are free swimming marine animals that are characterized due to umbrella shaped bells and trailing tentacles. They are found from surface waters to the deep sea. They are quite common in coastal zones.
Corals are marine invertebrates belonging to class anthozoa. They are found in compact colonies consisting of identical individual polyps. They secrete calcium carbonate to form a hard skeleton. They are exclusively marine and are found in the tropical oceans.
Roundworms or nematodes are a diverse animal phylum which are found in both terrestrial as well as aquatic conditions. Most of the species have adapted to different types of ecosystems such marine, freshwater and terrestrial environments. Many of the species occur as parasites and cause pathogenesis in most plants and animals.

Hence, the correct answer is option (D).

Note: Aquatic organisms are found to survive in the water habitats and different types of invertebrates and vertebrates are found in the aquatic environments. Some organisms such as hydra, jellyfish and corals are exclusively aquatic organisms while the round worms are found in terrestrial as well as aquatic habitats.