Question

One of the few egg laying mammal which has a poisnous stinger

Answer 1

Thanks for the question!

It is definitely a very interesting question to solve and do some brainstorming.

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$\textbf{Ornithorhynchus anatinus}$ or $\textbf{Duck-billed platypus}$ or $\textbf{platypus}$ are the only mammals (along with Echidna) which primarily lay eggs. The Duck-billed platypus has a beak or a bill which is broad and flat just totally similar to a normal duck, hence the name has been applied as Duck-billed platypus. A pinnae or the pair of pinnae are absent, both of the feet are webbed and has a flattened tail ehcih help and give them an edge over swimming, hence, they have been also referred as semiaquatic mammals, since they are both on land and in any water body or partly a terrestrial animal. The Mammary glands are present and there is absence of any nipples or teats which other mammals show for extra support in breastfeeding.
The Male platypus can be easily distinguished from the female one as the Male platypus contain or have a $\textbf{poisonous spur}$ or a poisonous stinger on each pair of Hindlimb, so, they are also coming under the only species which are actually "venomous mammals". The venom is discharged into by piercing the skin of a organism and is known to cause severe uncomfortable pain throughout that region which are released by the immune system of the platypus, the chemicals which contain Defensin like proteins or DLPs which are similar in chemical and physical structure. The organ is sometimes used as a dominant show when the breeding season between males and females are set off, this makes the venom to rise in the spurs and is used a weapon of choice against other participants (for selection of partners) or a offensive weapon to state a edge over other platypus for females.

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Hope it helps and solves your query!!