As the name suggests, Proto stands for primitive while Zoan means animal.They are unicellular in nature. However, the single cell has highly complex functions. Hence they are also referred to as the 'pinnacle of unicellular complexity'. they have a typical eukaryotic cell structure. Just the nucleus and the membrane bound organelles, form an integral part of the cell. Many of them possess food vacuoles, which are used to store food. And these cells do not have a cell wall. Are there any more special features. Many of them have additional features like cilia of flagellum for locomotion. Cilia are these tiny hair like structures which are present throughout the body. Flagellum on the other hand is usually a slender long filament, which is single or rarely multiple in number

Protozoa are dependent on other organisms as their food source. Only a few rare exceptions include the chlorophyll containing Euglena. It usually performs photosynthesis. But others lack the capacity to do so. Many organisms belonging to the protozoan group are well known parasites. They derive nutrition directly from the body of living organisms. So they do not kill the host, but do harm them severely! A few commonly known examples of protozoans include Amoeba, Euglena, Paramecium, and the disease-causing Plasmodium. This was about the third category that is the Protozoa.

Human Diseases Caused By Protozoan
Disease Protozona Vector Parts Affected and Symptoms
Pyorrhoea Entamoeba gingivalis Non, infection by lop kissing. Bleading of gums
African trypanosomiasis(sleeping sickness,gambian fever) Trypanosoma gambinse Tse-tse fly(Glossina palpalis) Blood and Nervious tissue.Man feels sleepy, may cause death.
Amoebic dysentery(Amoebiasis) Entamoeba histolytica None, infection by contamination Colon(intestine).Devlop loose motionwith blood, pain in abdomen.
Diarrhoea Giardia Non ,infection by contamination Digestive system causes loose motion, vomitting.
Kala azar or dumdum fever Leishmania donovani Send flies(Phlebotemus) Sleep and Liver enlarg and high fever devlops.
Filariosis or elephantiasis Wuchereria bancrofti Culex mosquito Swelling of leags,testes and other body parts.
Malaria Plasmodium sp. Female anopheles mosquito Periodacal attacks of high fever, pain in joints,accompanied by chill heavy perspiration and fast pulse.
Note:- Fishes like cat fish, Gambusia and aquatic birds eat mosquito larvae. Quinone, a product of Cinchona tree, is administered for treatment of malaria.