The Protist in which cell size decreases with each division are
A. Diatom
B. Dinoflagellates
C. Euglenoids
D. Slime molds

Answer Verified Verified
Hint: A particular Protist, when divided by mitosis, the daughter cells produced turn out to be smaller in size. These are the only organisms on this planet having a transparent, siliceous cell wall.

Complete answer:Diatoms are Protists i.e. belonging to the phylum Protista. Diatoms float on water as phytoplanktons and many aquatic animals feed on these. The specialized cells or spores called exospores are produced by diatoms that grow and develop to regain a normal size.
Diatom cells multiply (asexual reproduction) by mitotic divisions but their mitosis is quite unique. When they divide, each daughter cell has one valve and reproduction occurs by furrowing. So, after each cell division, the net size of the diatom gets smaller.

So, the correct option is A. Diatom

Note: These are unicellular and free-living algae. Some members form filaments, ribbons, or even star-shaped colonies. It has a cell wall made up of transparent, unique silica- often called ‘frustule’. Just like most other organisms, euglenoids, dinoflagellates, and slime molds also undergo normal mitosis in which the parent cell gives rise to equal-sized daughter cells.