On suction in Suctoria 



by 



J. A. KITCHING 



Department of ^oology, University of Bristol 



INTRODUCTION 



The Suctoria are a group of carnivorous Protozoa having tentacles by means of 

 which they hold and apparently suck their prey. I wish to discuss the mechanism of 

 suction. 



A suctorian tentacle normally consists of a sheath and an inner tube. The sheath 

 is apparently continuous with the surface of the animal, whereas the inner tube usually 

 extends a little way into the body of the animal, where it ends abruptly (Collin, 

 191 2; Noble, 1932). There is a bulbous or sucker-like expansion at the tip of the 

 tentacle, of a structure not yet convincingly described; in Tokophrya infusionum 

 minute papillae have been detected at the tip of the tentacle with the electron- 

 microscope (Rudzinska and Porter, 1953). 



Some species of Suctoria are particular as to their food. For instance Podophrya 

 fixa is only known to feed on hypotrich ciliates (Collin, 191 2, p. 253), and Discophrya 

 collini (Root, 19 15, as Podophrya collini) on holotrichs. Others, however, such as 

 Tokophrya infusionum, ingest a wide variety of Protozoa, including both flagellates and 

 ciliates (Iziumov, 1947). In some Suctoria the tentacles contract and extend vigor- 

 ously; in others the movements are extremely slow and for most of the time the 

 tentacles are motionless. When a suitable food organism touches the tip of one or 

 more tentacles, it is held. Sometimes it breaks away, but if it fails to do so within a 

 minute or so it falls victim to the suctorian. Some species of Suctoria appear to 

 paralyse their prey, as though by some toxic agent. The contents of the prey then 

 pass up the tentacles into the suctorian, the ingested material being held in food 

 vacuoles (Noble, 1932; Rudzinska and Porter, 1953), in which it is presumably 

 digested. 



THE HYDROSTATIC GRADIENT 



A rough estimate of the force necessary to drive the contents of the prey into the 

 suctorian predator can be derived from the rate of flow up the tentacles by means of 

 Poiseuille's formula. This estimate could be based on the decrease in volume of the 

 prey, but this is difficult to measure accurately. The increase in volume of the 

 suctorian is not by itself a sufficient index of the flow of material up the tentacles, 

 because some of the water so derived is evacuated by extra activity of the contractile 

 vacuole. However, the rate of flow up the tentacles can be estimated from the sum 

 of the increase in volume of the suctorian and the extra vacuolar output. From esti- 

 mates derived in this way for Discophrya piriformis, and on the assumption that 



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