Observations on the Occurrence of an Epizooic, Blue-Green Alga on the Chemoreceptor Setae of the Brown Shrimp, Crangon Crangon (L.)

The thin-walled setae on the outer rami of the antennules of decapod Crustacea are considered to be chemoreceptors. It is not known whether stimulatory molecules enter each seta through the cuticular wall or via an apical pore. In this paper evidence is presented that the antennular chemoreceptors of the brown shrimp, Crangon crangon (L.), bear apical pores. In some field and laboratory populations, however, the pores are blocked by an epizooic, blue-green alga and this provides a direct means of testing the hypothesis that the apical pore is important in the sensory process.