the.com/monotreme

means An order of egg-laying mammals — the platypus and echidnas — that nurse their young with milk despite hatching them from eggs like birds or reptiles.

from From Greek 'monos' (single) plus 'trema' (hole), meaning 'single hole' — a reference to the cloaca, the one all-purpose opening these animals use for excreting, urinating, and reproducing, rather than having separate exits like most mammals. The term was coined in the early 1800s as naturalists scrambled to classify the platypus, an animal so anatomically baffling that some suspected a hoax when the first specimen reached Europe.