Answer: monotreme

AnswerCrossword Clue
MONOTREMEPlatypus' classification
MONOTREMEDuckbill or echidna
MONOTREMEEgg-laying mammal
monotremea primitive Australian egg-laying mammal, eg a duck-billed platypus
monotremeA primitive mammal that lays large yolky eggs and has a common opening for the urogenital and digestive systems. Monotremes are now restricted to Australia and New Guinea, and comprise the platypus and the echidnas