Question

Which animal can't lay egg​

Answer 1

viviparous animal can't lay egg

Answer 2

There are three forms of reproduction in vertebrates: oviparity, viviparity, and ovoviviparity.

Oviparity is a form of reproduction where the mother lays undeveloped embryos in eggs, hard-shelled or soft. Oviparity is seen in reptiles (including birds), mammals (monotremes such as the platypus), fish, amphibians, and arthropods. This is demonstrated beautifully in the poster below:

Viviparous animals retain the fertilized egg inside the mother’s body and incubate the embryos, aided by a placental (nutritive) attachment of some sort, until they are developed into sort of “mini-adults”. The offspring are then birthed live. The majority of mammals are viviparous, as are some reptiles.

Also included within the viviparous are the ovoviviparous. This is sort of a mix between oviparity and viviparity; the young develop in and hatch from an egg, but from within the mother’s body. The animals are later born live. Ovoviviparity is seen in snakes such as pit vipers, and in many sharks. Another interesting example of ovoviviparity is shown in seahorses, where the male “gives birth” to the young:

If you consider depositing eggs outside of the body to be “laying an egg,” then only oviparous animals would fit your description. However, if you consider bearing young from an egg to be “laying an egg,” then both oviparous and ovoviviparous animals would qualify.