Question

Which among these is the correct combination of aquatic animals?
A. Trygon, whales, seals
B. Seals, dolphin, sharks
C. Dolphins, seals, trygon
D. Whales, dolphins, seals

Answer 1

All the above options come under the subphylum Vertebrata. They are further divided into Gnathostomata (bears jaw) and Agnatha (lacks jaw). The Gnasthomata are further divided into Pisces (bears fin) and Tetrapoda (bear limbs) the Tetrapoda are further divided into
-Amphibia
-Reptilia
-Aves
-mammals

While Pisces is divided into class
-Chondrichthyes
-Osteichthyes

Complete answer:
-Trygon: They are aquatic animals belonging to the class Chondrichthyes of superclass Pisces. Trygon contains poison sting. All animals under this class are poikilotherms meaning they can not regulate their own body temperature, they are viviparous and perform internal fertilization. Sharks also belong to this class.
-Whales: Whales are aquatic mammals. Belonging to the class Mammalia. Like other mammals, they breathe through the air through blowholes, warm-blooded, and their limbs are modified into flippers.
-Sharks: They are also aquatic animals belonging to class Chondrichthyes of superclass Pisces. Chondrichthyes skeleton is made up of cartilage. Their teeth are made up of placoid scales. Most sharks are heavy and they need to keep swimming to prevent themselves from drowning.
-Dolphins: Dolphins are aquatic mammals just like other mammals they breathe through lungs and come to the surface from time to time. limbs are modified into flippers.
-Seals: They are also aquatic mammals.

Hence, the correct answer is option (D).

Additional information:
The mammals are the most advanced animals on the planet they are present in every habitat. They bear mammary glands to feed their young ones. They all have limbs modified through evolution such as
Flippers, wings, some have very long nails for burrowing.

Note: Phylum Chordata includes those animals with a notochord either throughout or during early embryonic life. Other common features among chordates are as follows -
-Pharyngeal gill slits
-A dorsal hollow nerve cord