The Protozoa perform locomotion in four different ways, each with a particular type of locomotory organelles, and each characteristic of a different class of the phylum. The ways are: 1. Amoeboid Movement 2. Flagellar Movement 3. Ciliary Movement 4. Metabolic Movement.
Mode # 1. Amoeboid Movement:
It takes place with the help of finger-like pseudopodia which arise from the cytoplasm of the organism from any part of the body and may be withdrawn. In the pseudopodia cytoplasm flow in the direction of movement (locomotion) and thus, the organism moves forward.
Pseudopodium formation occurs in two ways:
(i) Profluent Type:
The ectoplasm protrudes out to form a short, blunt pseudopodium in which endoplasm flows. This type of locomotion is of lobose type in which a number of pseudopodia are formed in one direction or only one pseudopodium is formed. The latter is called of limax type.
(ii) Eruptive Type:
The ectoplasm and endoplasm break the surface of the body and flow out to form a rounded projection, called pseudopodium. This type of locomotion is explained by sol-gel theory (change in viscosity) of the cytoplasm. This theory was given by Hyman (1917) and later supported by Pantin (1923- 26) and Mast (1925).
According to them, the cytoplasm is distinguished into an outer gel layer, plasmagel and an inner fluid layer, plasmasol. The amoeboid movement of the organism is due to the conversion of plasmagel into plasmasol which flows forward into the projection and then again changed into plasmagel.
The amoeboid movement involves four processes which occur simultaneously:
1. The plasmalemma of the body sticks to the substratum.
2. Conversion of the plasmasol into the plasmagel (gelation) on the sides due to which a gelatinized tube is formed. Into this tube plasmasol continuously flows forward.
3. Conversion of plasmagel into plasmasol (solation) at the posterior end of the body.
4. The plasmagel of the gelatinized tube at the anterior end contracts and moves backward.
5. The plasmagel contracts at the sides and at the posterior end of the organism forcing the plasmasol forward.
6. Conversion of the endoplasm in to ectoplasm at the tip of the pseudopodium.
Mode # 2. Flagellar Movement:
This sort of movement is the characteristic of mastigophora or flagellated protozoans, e.g., Euglena. Flagellar movement is produced by continuous beating (i.e., lashing movement) of long, elastic flagella.
Following four types of flagellar movements have been movements have been recognized:
(i) Screw Propeller Theory:
According to Butschli, the spiral turning of the flagellum like a screw exerts a propelling action and pulls the animal forward. Spiral waves arise repeatedly from the base of flagellum on after the other and moving towards the tip.
(ii) Circular Beat Theory:
Metzner suggested that the flagellum beats in a circle tracing a cone and produces sufficient current to pull the animal forward.
(iii) Sideways Lashing Movement:
According to Ulehla and Krijsman (1925) the flagellum beats in a side-ways lash, which consists of an effective down stroke or bending and a relaxed recovery stroke or straightening. In the effective stroke the flagellum is held out rigidly with slight concavity in the direction of stroke.
In the recovery stroke, however, flagellum is strongly curved and is brought forward again. Due to such flagellar action, the animal moves forward. Generally the flagellum beats obliquely so that during forward movement, the animal also rotates on its longitudinal axis.
(iv) Undulating Movement:
The flagellum shows wave-like undulations. When such undulations move from tip to base of the flagellum, the animal moves forward and when they pass from base to tip, the animal move backward. If the undulating motion of the flagellum is of spiral type, the animal rotates in opposite direction.
Mode # 3. Ciliary Movement:
Ciliary movement takes place in ciliates (e.g. Paramecium) and the larvae of Suctoria. The movements of cilia are like that of flagella, having an effective down strokes and a recovery strokes. Unlike flagellum, the cilium bends in its full length. The movements of cilia create a current of water in the same direction in which cilia move. But the organism move in opposite direction.
Each cilium of the body beats independently. All the cilia of a transverse row move simultaneously (at one time), while the cilia of a longitudinal row do not beat at one time, but one after another (metachronously), producing a wave from front-backward. Thus, the animal moves forward in a spiral manner and the speed of movement are 400 to 2000µ per second. Ciliates are the fastest moving protozoans.
The movement of cilia is controlled by the myonemes (neuronemes) present in the ectoplasm. The basal granules of a row are connected with each other by an elastic longitudinal fibre, the myoneme. All the myonemes converge on a body, the motorium located near the cytopharynx. These myonemes control the movement of cilia. The basal granules, myonemes and motorium together form the neutromotor system in the Paramecium.
Mode # 4. Metabolic Movement:
The Protozoa possessing myonemes move by contraction of the body or stalk. Some flagellate (Euglena) perform wriggling or peristaltic movements by a wave of contraction and expansion passing over their body. Such movements have been termed euglenoid or metabolic movements. Similar movements met with in Gregarinida are known as gregarine movements. These occur due to the action of the myonemes. The mechanism and the physiology of myonemes are not understood well.