Observations on the leg receptors ofCiniflo (Araneida: Dictynidae)

Abstract

The electrophysiological responses to mechanical stimulation of the four commonly occurring types of hair sensilla on the legs of the cribellate spiderCiniflo are described. The long, straight ‘tactile’ hairs respond preferentially to depression with activity from two phasic receptor units, one of which is sensitive to higher movement velocities than the other (Fig. 3). The units innervating the large spines respond only during erection. There is a fast adapting phasic unit and a slower adapting phaso-tonic unit (Figs. 4 and 5). It is suggested that these spines may serve partly as haemocoelic pressure monitors. The delicate trichobothria respond to small movements in all directions with directional responses from three phasic units, and are the only hairs showing true, directional sensitivity (Figs. 9, 10 and 11). The curved, blunt-tipped ‘chemoreceptive’ hairs show activity from one phasic unit when the hair is deflected in any direction away from its rest position (Fig. 8). In all cases, the number of physiologically detectable cells is one less than has been shown to be present ultrastructurally. The possible significance of these observations in relation to general araneid behaviour is discussed.