Chemotaxis and lunge-feeding behaviour of Dendronotus iris (Mollusca: Opisthobranchia)

Abstract

This study provides evidence that Dendronotus iris Cooper can detect odours of Pachycerianthus fimbriatus at a distance. When searching for food, D. iris crawls forward, waving its head and large rhinophore stalks. It exhibits chemotaxis and can select the scented arm of a Y-maze, crawling against current flow when the water contains food extracts. In the natural environment, D. iris is able to locate P. fimbriatus in both the presence and absence of currents. Feeding behaviour is described under three phases from observations made in situ and in aquaria: (i) In the detection of food and during the food-seeking phase, D. iris advances towards its prey while waving its head. (ii) After contact has been made, the opisthobranch centres its oral region by alternatively touching left and right frontal processes to the tentacles of the prey. Head waving continues with upward movement and anterior protraction (i.e., lunge) of the oral region. (iii) Finally, the bite-strike response is exhibited, followed by further bite strikes and intermittent closings of the masticatory margins. Retraction of the radula brings anemone tentacles through the opened masticatory margins. The masticatory margins function to cut food into pieces, which are then thrust into the esophagus by the radula.