They are a very diverse group of organisms, but all have vesicular membrane structures underneath their cell membrane, and are all related by ancestry. The apicomplexans are not well studied except Plasmodium , the causative agent of malaria, probably the single most important disease in man. Ciliates e.g. Paramecium . These are common, familiar organisms. Cilia are really just short, numerous flagella organized by a complex microtubule network just under the cytoplasmic membrane.
Ciliates are very morphologically complex.
Dinoflagellates Usually photosynthetic flagellates - the 2 flagella are oriented at right angles, and they often have cellulose cell walls. Although they are photosynthetic and have chloroplasts, like the euglenoids they are not related to plants and aquired their photosynthetic symbiontic cyanobacteria independently of plants. They are quite versitile, and often have complex life cycles. They are common symbionts of animals, such as reef-building corals and marine clams. On the other hand, they are also the causitive agent of red tide and ciguatera poisoning.