Sensitivity to Movement and Vibration of Water in the North Sea Shrimp Crangon Crangon L.

Abstract

The common north sea shrimp Crangon crangon was studied both with scanning electron microscopy (SEM) and electrophysiology to determine its ability to detect and process neuronal displacement signals in the surrounding water. SEM showed a large population of small, hair-type sensilla of 20-500 Am length found on antennae, carapace, walking legs, abdominal tergites, telson, and inner and outer uropods. Serrate setae and another prominent sensory organ of presumed chemo- and/or mechanoreceptive function were located on the subchelate leg. Microelectrode recordings from sensory roots and connectives of the ventral nerve cord revealed that the large mechanoreceptive hairs on the uropods must be dually innervated, with the two sensory cells responding 180? out of phase to each other. Sensory cells responding to identical phases of wave motion converge onto phase-specific intereurons. Directional coding by mechanosensory interneurons of the abdominal ventral nerve cord varied from directional to unselective. Sensitivity to vibration of water, sand, and the buried animal itself is maximal at 170 Hz; a fixed behavior consisting of a fast backward flicking of the large second antennae was most readily elicited at this frequency, with an absolutely lowest threshold of acceleration of 81 cm/s2, corresponding to 0.7 ,m amplitude of particle displacement in the surrounding sand and water. The results suggest a close relationship between mechanosensory pathways in crayfish and shrimp, and recommend shrimps as useful objects for behavioral tests of sensory capacities of crustaceans.