Although attached to the substratum by the basal disc and usually standing erect, the Hydra has several methods of locomoÂtion. Usually it bends down and attaches the tentacles to the subÂstratum with the help of the glutinant nematocysts.
It now releases and removes the basal disc to a new position and again stands up by disengaging its tentacles. This type of locomotion is known as walking. It may bend its body and perform looping movement like that of a leech (Fig. 62 A). When in a hurry, the animal runs by performing a series of somersaults (Fig. 62 B).
Sometimes it walks inverted by using the tentacles as legs. Again it may glide considerably by dragging the basal disc—the cells of which have special power of throwing out pseudopodia like an Amoeba.
Occasionally Hydra secretes a bubble of gas under its basal disc and floats about by the hydrostatic action of the gas bubble. A Hydra may climb by attaching its long tentacles to a distant object. Then releasing the basal disc and contracting the tentacles the body is drawn up, and it resumes its normal position on the new substratum.
It is to be noted that:
(1) Fixation is effected by the mucus- secreting gland cells in the epidermis of the basal disc and the glutinant nematocysts with sticky threads on the tentacles.
(2) Shortening the length of the body is due to the contraction of the muscular processes of the ectodermal epitheliomuscular cells.
(3) Increasing the length of the body is produced by contracting the muscular processes of the endodermal nutritive-muscular cells.
Well , this was indeed a good question as I too got to know it’s locomotion just now after searching upon it …thanks @Akshitha