Hydra pirardi contracts in response to light and mechanical agitation. The animals show a reduction in the number of contractions in response to mechanical agitation on repeated testing but continue to contract in response to a light stimulus. Excision of all the tentacles of the animal completely inhibits contraction in response to mechanical agitation but does not affect contraction in response to light. The results of these experiments suggest that H. pirardi has different receptors for light and for mechanical agitation and that the control mechanisms for the contraction responses to these two stimuli are independent.

http://science.sciencemag.org/content/sci/139/3556/760.full.pdf

Behavior in Hydra: Contraction Responses of Hydra pirardi to Mechanical and Light Stimuli

Osmoregulation in fresh-waterHydra

Osmoregulation in Hydra: Column contraction as a function of external osmolality

Three environmental zones which can influence the activation of the feeding response of Hydra littoralis are termed the macro-, micro-, and ultramicroenvironment. The first consists primarily of the ions in the bulk medium, and of dissolved gases. The microenvironment is the area immediately surrounding the hydra; its composition is influenced by substances emitted from and taken up by the animal. The third zone, the ultramicroenvironment, is presumed to be made up of a thin shell of ions in the medium that are attracted to the charged surfaces of the animal.

Through a physicochemical study of these environments, we have determined: (1) the presence of ionizable groups at the receptor site which may be involved in the binding of glutathione; (2) the role of potassium and other ions in influencing the feeding response; and, (3) the possible existence of charged surfaces on hydra surrounded by a pH shell. Further, these experiments help to resolve many seemingly inconsistent reports dealing with the feeding behavior of hydras.

/pdf/some-physigochemical-aspects-of-the-macroand-1eqz33gibs.pdf

Raymond H. Reis

Papers

Spontaneous Change of Form of Pelmatohydra oligactis

Spontaneous Change of Form of the Green Hydra, Chlorohydra viridissima

Rhythmic Behavior Patterns in Pelmatohydra oligactis

Factors Affecting Change of Form in Pelmatohydra oligactis. III. Presence of Developing Bud

Factors affecting change of form in Pelmatohydra oligacitis; depression.