Sensitivity of intact and antennule amputated copepods to water disturbance

Abstract

Behavioural observations were made on restrained individuals of the copepod Temora longicomjs Muller, to investigate the range over which sensitivity to water disturbance, in the form of fine jets, could be detected T longicornis was most sensitive to jets in front of it; jets behind were largely disregarded. When placed behind or beside the copepod, positions from which it was less sensitive, the larger or closer the jet, the more frequent was the response. When water flowed in the unnatural postero-anterior direction, the same pattern of sensitivity was shown to disturbances applied at various orlentations. Hence propagation of the disturbances was not related to the direction of the water current, nor to its speed. The suspected mechanosensory setae of the antennules are the most likely receptors to be implicated in the detection of f l u ~ d disturbances, since amputation of the antennule or antennules greatly reduced the sensitivity of the copepod to jets. Bilateral antennular amputation did not entirely prevent escape responses from being elicited; this indicates there must be mechanoreceptors present on other areas of the body. Furthermore, all areas of the copepod are very sensitive to direct stimulation by water jets.