monotreme

Any of various egg-laying mammals of the order Monotremata of Australia and New Guinea, whose only living members are the platypus and the echidnas.

Same as monotrematous: as, monotreme mammals; a monotreme egg.

A member of the Monotremata, as a duck-mole or prickly ant-eater.

One of the Monotremata.

A mammal that lays eggs and has a single urogenital and digestive orifice. Only the echidnas and platypuses are included in this group.

Having a single trema, or aperture

the most primitive mammals comprising the only extant members of the subclass Prototheria