The best understood contractile vacuoles belong to the protists "Paramecium", "Amoeba", "Dictyostelium" and "Trypanosoma", and to a lesser extent the green alga "Chlamydomonas". Not all species that possess a contractile vacuole are freshwater organisms; some marine, soil microorganisms and parasites also have a contractile vacuole. The contractile vacuole is predominant in species that do not have a cell wall, but there are exceptions (notably "Chlamydomonas") which do possess a cell wall. Through evolution, the contractile vacuole has typically been lost in multicellular organisms, but it still exists in the unicellular stage of several multicellular fungi, as well as in several types of cells in sponges (amoebocytes, pinacocytes, and choanocytes).