Why do we classify both snakes and turtles in the same class?

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

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

Write true or false for the following statement:
The animals belonging to phylum $Mollusca$ have a peculiar water-driven tube system that they use for moving around.

The skeleton is made entirely of cartilage in

Give reasons:
$(a)$ Animals of phylum Platyhelminthes are called flatworms.
$(b)$ Bryophytes are called amphibians of the plant kingdom.
$(c)$ Fungi are called saprophytes.
$(d)$ Bacteria and tapeworms are very different in their body design.
$(e)$ Plants like Pinus and deodar are called gymnosperms.