The circulatory system has evolved from open to closed type in Animal kingdom. Which Phylum can be called first to represents closed circulation?

Pinna is part of external ear and it is found in mammals. Do aves and reptiles show external ear in any form?

Birds need to keep their body light to help in flying. Hence, they show presence of some organs only on one side. How their skeleton helps in reducing their weight?

Crab and snail both have a protective covering. Is it made up of the same material?

Sponge and sea star show calcareous protective material. Do they belong to the same Phylum?

Fish and snake both have scales. How do these scales differ from each other?

Lower Phyla like Arthropods and Cnidarians show metamorphosis. Is it also found in any class of Phylum Chordata?