Why are bats not placed in birds?

Hard calcium carbonate structures are used as a skeleton by

Which group of animals have haemocoel?

$(a)$ Associate any three phyla of Animalia with triploblastic body organisation and bilateral symmetry.
$(b)$ State the meaning of triploblastic body organisation and bilateral symmetry.
$(c)$ On the basis of presence or absence of coelom,compare the three phyla answered in $(a)$.

Classify the phylum Vertebrata into their further groups by giving two characteristics of each.

Name two mammals which lay eggs. Between which two phyla do they serve as connecting link? Name a mammal which gives birth to poorly developed young ones.