THE AMBUSH BEHAVIOR OF CERCARIAE OF SOME MARINE TREMATODES

The behavior of cercariae of Podocotyle atomon and Levinseniella brach ysoma, the second intermediate hosts of which are littoral gammarids, was studied experimentally. The behavior of studied cercariae was obse rved to consist of passive and active periods. In the first one larvae have the <<waiting posture>>, a sedentary state at which larvae are v ertically attached to substrate by caudal appendages. The second stage includes reactions of cercariae to vibration or movement or water. Vi bration both of vibrator (in laboratory) or the pleopodes of Gammarus (in situ) causes the reaction of <<search>> or <<attack>> depending on distance from the source of vibration. Larvae attach themselves to th is source if the latter is within the reach of cercaria. A larva react s to water current when its velocity is more than 8-10 cmps. The react ion is protective and was observed as additional attachment to substra te. The behavior of studied cercariae can be regarded as the <<ambush> > one because of the lack of distinct raid and pursuit of a host in re sponse to water vibration and of distinct manifestation of <<attack>> reaction only at little distance from the source of vibration.