The food reactions of the infusorian Spathidium spathula

Abstract

Spathidium spathula is an holotrichous infusorian whose sole diet consists of smaller ciliates, chiefly species of Colpidium. If the truncated anterior end of a Spathidium, which is swimming forward and revolving on its long axis, happens to come into direct contact with a Colpidium, the latter usually becomes motionless at once and its protoplasm shows signs of pathological changes.

Paralysis and death of the prey is apparently brought about by the liberation of a specific substance from the oral region of Spathidium which is toxic to small ciliates. Various authors have ascribed this result to trichocysts about the peristome, but as a matter of fact none are present. However, a number of rodlike bodies can be demonstrated in the thickened rim of the peristome which may represent the seat of the poison. One is at liberty to interpret these bodies as “trichocyst material,” though the poisonous nature of trichocysts, even in Paramecium, remains to be demonstrated.

The paralysis of a Colpidium by a Spathidium results in a marked change in the latter's behavior, which up to this instant has comprised random swimming movements. If the Colpidium happens to remain against the truncated anterior end, the Spathidium forthwith proceeds by means of the thickened edges of the peristome to force its prey down through the slit-like mouth into the interior of the cell. On the other hand, if the Colpidium is not instantly rendered motionless and becomes removed a short distance from the oral region of its captor, the latter institutes a series of rapidly repeated avoiding reactions. This behavior has a tendency to keep the animal in the general vicinity of its quarry because each time the Spathidium starts away its forward progress is checked by the reaction.