A Taxonomic Review of Heterotrophic Protists Important in Marine Ecology

Abstract

The easy distinction between higher animals and higher plants led earlier biologists to extend the animal and plant kingdoms down to the unicellular level and separate algae taxonomically from protozoa. There-after one group was studied by botanists and the other by zoologists, and the separation was perpetuated in spite of the difficulty of defining a boundary between algae and protozoa. Closer study raised many questions about the taxonomy of these ‘lower’ organisms. The current view of cellular evolution (e.g. Woese 1987; Sleigh 1989) is that among the first cells (progenotes) were prokaryotes of different types which evolved to give the diversity of bacteria; other progenotes gave rise to nucleated, and probably amoeboid, phagotrophic eukaryotes with cytoskeletal systems, and at an early stage flagella and golgi systems evolved. Most eukaryotes developed symbiotic associations with aerobic bacteria to form mitochondria, different groups having different forms of internal cristae.