List of six examples of Amoeboid Protozoans.
Example # 1. Amoeba Proteus-The Proteus Animalcule:
Amoeba was discovered by Russel von Rosenhoff in 1755. H.I. Hirschfied (1962) has given a detailed account of the biology of Amoeba. It is found in fresh water. Types of pseudopodia are lobo podia. A contractile vacuole is present for osmoregulation.
Mitochondria are often seen aggregated around the contractile vacuole of Amoeba. Cytoplasm is differentiated into endosperm and ectoplasm. Endoplasm is further differentiated into plasmagel and plasmasol. The body is covered by plasma lemma. Nutrition is holozoic.
Sexual reproduction is not known. Four methods of ingestion are present in Amoeba:
(i) Import:
This is passive food-ingestion.
(ii) Invagination:
Invagination tube is formed to take food particles.
(iii) Circumfluence:
Food particles are less active.
(iv) Circumvallation:
Prey is very active. The contents of food vacuole in Amoeba first become acidic then alkaline. If an Amoeba is placed in distilled water, its contractile vacuole works faster. If a fresh water Amoeba is placed in salt water, its contractile vacuole will disappear. Sol-gel theory of amoeboid movement was given by Hyman, and supported by Pantin and Mast.
Example # 2. Pelomyxa:
It is also known as giant amoeba. The size is about 2.5 mm long. Pelomyxa occurs in fresh water. Nutrition is holozoic. The chief food article is diatoms. Nuclei are 100-1000 in number. Both non-contractile and contractile vacuoles occur. Asexual reproduction occurs by fission. Sexual reproduction takes place by the formation of uninucleate internal gametes.
Example # 3. Entamoeba Histolytica:
Lamble (1859) discovered Entamoeba histolytica. Losch (1875) discovered its pathogenic nature. The life cycle of Entamoeba histolytica is mono-genetic (single host life cycle). It resides in the upper part of the human large intestine and causes the disease known as amoebic dysentery or amoebiasis.
The symptoms of the disease are abdominal pain, repeated motions with blood and mucus. The parasite is with generally one pseudopodium. Contractile vacuole is absent as there is no need of osmoregulation. It feeds on red blood corpuscles by damaging the wall of large intestine and reaching the blood capillaries.
It produces ulcers. The parasite can also reach other body organs. Multiplication is by binary fission. Entamoeba histolytica has two forms, magna (trophozoite) — pathogenic form found in the mucosa and sub mucosa of intestine forming ulcers and minuta— non-pathogenic form found in the lumen of the intestine.
Minuta form encysts. A mature cyst is called tetra-nucleate cyst. It has four nuclei and two chromatoid bodies. Tetra nucleate cyst is the infective stage. It is important to note that only one young amoeba with four nuclei hatches out from a cyst of E. histolytica. However, single cyst of E. histolytica produces eight amoebae. Most effective medicine for amoebiasis is Metrogyl or Flagyl.
Example # 4. Radiolarians:
They are exclusively marine, free floating sarcodines having a central perforated capsule and a fine framework or skeleton of silica. The protoplasm is differentiated into intra-capsular and extra capsular parts. The extra capsular part develops pseudopodia for locomotion and ingestion.
Pseudopodia are fine thread like radiating strands which may be axopodia or filopodia. The intra-capsular part contains nuclei, small vacuoles and reserve food that represents the reproductive part.
Reproduction occurs through binary fission and swarm spores. Examples, Acanthometra and Collozoum. Radiolarian ooze is the deposit of radiolarian skeleton which is put to commercial use like diatomaceous earth as filtering agent and abrasive (rubbing).
Example # 5. Foraminifera’s:
They are bottom dwellers, marine or fresh water sarcodines which possess a calcareous shell having one or more chambers with one or more perforations.
Protoplasm flows out of the pores to form a thin covering around the shell. The latter develop pseudopodia for creeping and ingestion. Pseudopodia are narrow thread like branched and anastomosing. They form a network (reticulopodia). Reproduction occurs by binary fission, multiple fission and flagellate gametes (syngamy). Examples, Globigerina and Elphidium (= Polystomella).
Calcerous foraminiferan shells collect at the bottom and form a forminiferan ooze. With time, the foraminiferan ooze changes to limestone rocks. The same are used as building material, e.g., Egyptian pyramids. Fossilised foraminiferan shells often occur in petroleum bearing formations.
Example # 6. Heliozoans:
They have spherical structure and were previously called sun-animalcules. The fine pseudopodia are called axopodia. The pseudopodia radiate. Heliozoans may be naked or with skeleton with siliceous scales or spines. Actinophrys, the sun organism is a common shell less heliozoan.
