Monotreme and Platypus

Monotreme noun - The most primitive mammals comprising the only extant members of the subclass Prototheria.

Platypus and monotreme are semantically related. In some cases you can replace term "Platypus" with "Monotreme", this nouns are similar.

Platypus noun - Small densely furred aquatic monotreme of Australia and Tasmania having a broad bill and tail and webbed feet; only species in the family Ornithorhynchidae.

Monotreme and platypus are semantically related. You can use "Monotreme" instead a noun "Platypus".