Question

Which of the following are exclusively marine animals?
A) Cnidarians
B) Echinoderms
C) Molluscs
D) Arthropods

Answer 1

Hint: The animals which inhabit the sea (saline water) are called marine animals. Some animals can both live in aquatic as well as terrestrial habitat.

Complete Answer:
To solve this question, we must know about the phylum in which the animals are exclusively marine and what specific feature helps them to sustain the salty environment.
There are many organisms which can survive in both marine and aquatic habitats. For example Phylum Cnidarians- The animals are predominantly marine but many can also found in freshwater. For example hydra, corals etc.
They have special structures for capturing prey. Phylum Mollusca is the phylum of invertebrates. They are the largest marine phylum but many molluscs are freshwater and terrestrial.
For example snail, squid, octopus. They have slimy skin and some have shells. Arthropods is the largest phylum in the animal kingdom. They are invertebrates with hard exoskeleton. For example crabs, lobsters, cockroach, bees etc.
They are found in marine, fresh water as well as terrestrial habitat. Some animals like starfish, sea urchin etc are found in the sea bed, deep oceans. They have a specialised water vascular system which helps them to survive in an extreme saline environment.
So these organisms are exclusively marine and are not found in freshwater or terrestrial habitats.

Thus, the correct answer is (B). All Echinoderms like starfish, sea cucumber etc are exclusively marine.

Note: Water vascular system is composed of canals which are connected to numerous tube feet. The canals of the water vascular system contain sea water. It generates a hydraulic pressure which helps the organism in locomotion.