Which type of organism lacks a cell wall and was previously...

Kingdom Protista has brought togetherChlamydomonas, Chlorella (earlier placed in Algae within Plants and bothhaving cell walls) with Paramoecium and Amoeba (which were earlier placedin the animal kingdom which lack cell wall). It has put together organismswhich, in earlier classifications, were placed in different kingdoms. Thishappened because the criteria for classification changed. This kind ofchanges will take place in future too depending on the improvement in ourunderstanding of characteristics and evolutionary relationships.