The phylum in which organisms contain a pseudocoelom is

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

State whether the following statement is true or false:
The animals belonging to phylum Nematoda contain only tissues and no real organs.

Name the phylum to which Leech and Earthworm belong.

Differentiate between the following:
$(a)$ Tube system of feather star and canal system of $Euplectella$
$(b)$ Skeleton of shark and sea horse
$(c)$ Respiratory organs of tadpole and frog
$(d)$ Forelimbs of birds and lizard
$(e)$ Skin of tree frog and human

Define evolution.