Movement

Abstract

Most free-living Protozoa possess the ability to perform locomotion, and even the sedentary forms are capable of movement, though in the Suctoria active locomotion from one locality to another is restricted to the early stages of the life-cycle. Different means of achieving movement have evolved among the free-living groups, the most marked contrast being between the Sarcodina on the one hand and the ciliated and flagellated Protozoa on the other. Characteristically the sarcodines possess pseudopodia, which vary structurally among the classes and orders of naked and shelled amoebae. Inevitably the gross movements between amoebae with skeletal structures and those without will appear distinctly different, since skeletal structures impose limitations on the type and speed of movement, as a function of test or shell shape and weight. The ciliates and flagellates have locomotory organelles which are structurally similiar. Typically flagellates have only one or two flagella, whereas in the ciliated Protozoa cilia are numerous and consequently a complex system co-ordinating ciliary beat has evolved.