In this article we will discuss about the four main types of locomotion in protozoa. The types are: 1. Pseudopodial Movement 2. Flagellate Movement 3. Ciliary Movement 4. Peristaltic Movement.
Type # 1. Pseudopodial Movement:
Some protozoon’s move with the help of pseudopodia. Pseudopodia are blunt, fingerlike temporary protrusions of the cytoplasm. These may be variously shaped. Large numbers of pseudopodia are present on the body surface of some individuals.
In case of Amoeba, the pseudopodium is known as lobo podium. The pseudopodium, which is in the advancing direction and in contact with the substratum, helps in locomotion.
The pseudopodium is fixed on the support by some adhesive secretion and the protoplasm of the body gradually flows into it. As to the mechanism of pseudopodia movement, the most accepted view is change of viscosity (Hyman). It states that sol-gel conversion initiates movement in the protoplasm.
The ectoplasm—where a pseudopodium is formed—is dissolved by the formation of an acid and the endoplasm flows. New pseudopodia appear and, by the repetition of the process, the animal slowly creeps forward. In Polystomella, the pseudopodia are known as reticulopodia (branching).
Type # 2. Flagellate Movement:
Certain protozoon’s move with the help of flagella. Flagella are whip-like structures in the formation of which cytoplasm takes part. These are usually 2-4 in number. A flagellum has an inner stiff structure, known as axoneme, which is surrounded by a protoplasmic sheath.
Euglena moves by the rapid lashing movement of the single flagellum, .which is placed at the anterior end of the body and is known as tractellum. In many, cases, flagella act as small oars. The most plausible mechanism, as suggested by Lowden’s; is that the basic function of a flagellum is to produce rotation of the organism on its major axis, along with a mechanism which directs the animal.
Type # 3. Ciliary Movement:
Some protozoon’s move with the help of cilia. Cilia are small hair-like structures, present usually in large numbers on the body surface. In some cases (Vorticella), the cilia are restricted only in a concentric circlet at the distal end of the body. Cilia are usually arranged in definite rows.
A cilium has practically the same histology as that of a flagellum. The Paramoecium moves forward in a rotating fashion by the beating movement of the cilia. The cilia act as small oars and the backward strokes are swift, which push the animal forward.
Type # 4. Peristaltic Movement:
Some protozoon’s move with the help of myonemes. Myonemes are small thread-like contractile fibrils usually located in the inner layer of ectoplasm. In Monocystis, the contraction of the fibrils is responsible for the contraction of the pellicle and the animal slowly moves forward in a jerking fashion.
Protozoa embraces a large number of varied individuals. Different forms of locomotory organelles are present in different stages of the life of the same animal. The members of the subphylum Sarcodina possess pseudopodia in the adult stage but, in the early stages, some of them bear flagella, which is the characteristic locomotory organelles of the subphylum Mastigophora.
There are some colourless mastigophores, which are permanently amoeboid, closely resembling amoebae but have a long flagellum at the same time. Such phenomenon indicates the possible ancestry of protozoa to a unicellular animal, which was capable of assuming either the amoeboid or flagellar phase.