Monotremes are mammals that reproduce by laying eggs, and like the platypus, an echidna is an egg laying mammal. Given these facts, a platypus is an example of  among the following options:
- a reptile
 - animals
 - an amphibian
 - a monotreme
 - killing insects
 - insects
 - murmur
 - an arachnid


 

    a monotreme     