Name the phylum to which Leech and Earthworm belong.

State the reason for the following:
$(i)$ Nematodes have a pseudocoelom.
$(ii)$ Arthropods have an open circulatory system.
$(iii)$ Echinoderms are named as such.

Give reasons for the following:
$(a)$ Echidna and Platypus lay eggs but are considered as mammals.
$(b)$ Birds have pneumatic bones.

Label $a, b, c$ and $d$ given in the figure. Give the function of $(b)$.

Two-chambered heart occurs in

Find out the false statement.