Q.Water vascular system is the characteristic of which group of the following:

The correct option is (c) Echinodermata.

The water vascular system is the most distinctive feature of the echinoderms. It is a unique system of fluid-filled canals and tube feet that helps in locomotion, in capturing and moving food, and in respiration. None of the other groups listed has it: Porifera possess a water-transport (canal) system with ostia, spongocoel and osculum — which is a different structure — while Ctenophora move by comb plates and …

The water vascular system is the single most distinctive feature of the echinoderms. It is a unique arrangement of fluid-filled canals connected to tube feet, and it serves the animal in three ways at once: it helps in locomotion, in capturing and moving food, and in respiration. Because no other phylum possesses this system, it points unambiguously to Echinodermata.

Checking the other options confirms the choice:

• (a) Porifera. Sponges have a water-transport, or canal, system in which water enters through pores called ostia, passes into the spongocoel, and leaves through the osculum. This is a different structure and is not the water vascular system.
• (b) Ctenophora. These marine comb jellies move using eight external rows of ciliated comb plates, not a water vascular system. …

Method: Systematic option-elimination

Rather than recalling the fact directly, test all four options against the single defining feature named in the question and eliminate each wrong one on its own known evidence.

The question names one specific structure — the water vascular system — and asks which phylum it belongs to.

• (a) Porifera: sponges are known for a water-TRANSPORT system (ostia → spongocoel → osculum), which involves water and canals but is used for simple filtering, not tube-feet locomotion. Different structure, different name — eliminate.
• (b) Ctenophora: comb jellies move using external rows of fused cilia called comb plates — no internal water-filled canal system with tube feet is involved. Eliminate.
• (d) Chordata: this phylum is defined by the notochord, dorsal nerve cord and gill slits — nothing about a water-powered canal-and-tube-feet system. Eliminate.
• (c) Echinodermata: by process of elimination, this is the only option left, and checking it directly confirms the match — echinoderms possess a unique network of fluid-filled canals connected to tube feet, used for locomotion, feeding and respiration, exactly matching the question's description. …