ABSTRACT
Gorgonocephalus arcticus, a basket star from the deep St. Lawrence Estuary shows intensity and tactile discriminatory abilities. The pinpoint mechanical stimulation of the disk induces a succession of reactions involving general arm coiling and covering of the disk by radii. The statistical comparison between temporal development of arm movements provoked by different intensities of stimuli demonstrates that G. arcticus reacts faster and stronger to a strong pressure than to a light or intermediate one. A pressure inflicted to an arm does not generate a global reaction but a localized and slow movement of the surrounding ramifications. In the case of a simultaneous double-site stimulation, a complete reaction, including covering of the disk, occurs only when both stimulations are inflicted to the radial shield. When the two stimuli involve adjacent arms, the same arm or an arm and the disk, almost no reaction is observed. A discrete local activity is perceptible after successive stimulation of two adjacent arms. This study presents the first behavioural observations of mechanosensitivity made on basket stars. These ophiuroids seem to develop a more complex pattern of reactions than the one observed in unbranched brittlestars, which could suggest a different level of organization of the nervous system.
