Sounds like a reptile to me.
Platypus eggs are soft and leathery, rather than hard-shelled.
There is no such thing as a "cleidoian egg." It may have been misspelled or misheard. If you meant to ask about a "cleidoic egg," it is a type of egg found in reptiles and birds that has a shell and several extra membranes to protect and nourish the developing embryo.
The animal hatched out of the largest egg will typically be larger in size compared to the animal hatched out of the smallest egg at birth. As they grow, this size difference may increase significantly depending on the species. For example, a bird hatched from a larger egg may end up much bigger than a bird hatched from a smaller egg.
Zygote is immediately produced when an animal's egg cell is fertilized by the sperm.
The largest cell in the animal kingdom is the ostrich egg cell. It is visible to the naked eye and is about 6 inches in diameter.
The egg of a platypus is leathery. It is not hard-shelled like a bird's egg.
Turtle eggs (and tortoise eggs) can be either hard or soft-shelled, depending on the species.
A bluebird.
to protect them from pridators
Birds lay normal, hard-shelled eggs while reptiles usually lay eggs with a leathery shell that is flexible.
Monotremes are egg-laying mammals, and their eggs are not hard-shelled, but leathery. The monotremes include the platypus and echidna.Reptiles also lay rubbery/leathery eggs.
The primary function - is to contain the developing embryo and its nutritional yolk-sac until the foetus is ready to emerge. That applies whether it's a hard-shelled egg like a bird, or a soft-shell like a reptile.
Reptiles, particularly turtles, produce hard-shelled eggs that mature outside the mother. These eggs are typically laid in nests on land, where they undergo incubation until they hatch. The hard shell provides protection to the developing embryo from environmental conditions and predators. Other animals, such as birds, also produce hard-shelled eggs, but the question specifically pertains to reptiles.
Platypus eggs are soft and leathery, rather than hard-shelled.
The eggs laid by monotremes (egg-laying mammals) are still called eggs. They are soft-shelled and leathery, rather than hard-shelled like birds' eggs.
Reptile eggs are soft-shelled so that the babies can break out of the shells. Bird eggs are hard-shelled, because baby birds use their beaks to crack the shells of their eggs, but since reptiles don't have beaks to use to break their shells, their eggs have to be soft-shelled.
Horses, flys, and dogs