Mosaic cleavage occurs in

The correct option is A Echinococcus
Mosaic cleavage is also known as determinate cleavage. As the name suggests the cells of the blastocyst have a pre-decided fate which means any cell of the blastocyst cannot develop into an individual animal.

This type of cleavage is generally seen in the protostomes.

When the cells are dividing in the determinate cleavage they take up a mosaic shape that's why the name mosaic cleavage.

As the three options include the animals belonging to the deuterostomes we are left clear with the last option.

So, the correct option is 'Echinococcus.'