To which class of Animalia does the housefly belong? Mention any three characteristic features of this class of animals. Give two other examples of this class of animals.

$X, Y$ and $Z$ are living organisms.
$(a)$ Identify the group to which they belong on the basis of following features:
$(i)$ $X -$ Microscopic,unicellular,prokaryotic.
$(ii)$ $Y -$ Microscopic,unicellular,eukaryotic and shows locomotion with the help of pseudopodia/flagella.
$(iii)$ $Z -$ Multicellular,filamentous,eukaryotic,autotrophic and aquatic.
$(b)$ Which amongst the above is most advanced?
$(c)$ Name one organism each belonging to the groups of $X, Y$ and $Z$.

Write the most striking features of the following phyla:
$(i)$ Arthropoda
$(ii)$ Amphibia
$(iii)$ Porifera

The book $Systema \text{ } Naturae$ was written by:

State whether the following statement is true or false:
Gymnosperms are usually perennial,evergreen,and woody.

$A$ student enters the museum and observes the animal specimens. He looks at the one marked 'whale' and calls it a type of fish. How will you explain to him that whales and fishes belong to two different classes? List any three distinguishing features to justify your statement.