The Response of A Hydroid to Weak Water-Borne Disturbances

Open Access
Publisher Website
Google Scholar
Abstract
1. Syncoryne mirabilis polyps rapidly bend toward the source of a mechanical disturbance in their vicinity. A small moving copepod a few millimeters from the polyp creates sufficient stimulus to evoke this response. 2. The hydroid will respond to a mechanical pulse from an electrically driven prodder as well as to single movements of the prodder either toward or away from the polyp. With the prodder 0.5 mm. from the polyp mid-line, threshold displacement of the prodder is only 2.5-3µ. Repeated pulses of increasing amplitude, initially below threshold intensity, will not evoke bending if the frequency is over 5/sec. This means that stimuli which cause no overt response can still inhibit polyp bending to normally supra-threshold subsequent stimuli. 3. A polyp will not respond to slow currents of water, but will bend towards the source of sudden jets of water directed at it. 4. The capitate tentacles are not necessary for the movement perception, but after their removal the threshold is raised and the accuracy of bending reduced. The response does not require that the polyp be attached to a fixed stalk; it also occurs in isolated polyps floating in a density gradient. 5. The hypothesis is presented that polyp bending is due to unequal stimulation of opposite sides of the polyp because of decreasing stimulus intensity with increasing distance from the source of disturbance.

This publication has 7 references indexed in Scilit: