Fine Structure of the Organ of Bellonci (SPX) in Boreomysis arctica (Kroyer) (Crustacea, Mysidacea)

The organ of Bellonci (oB) in Boreomysis arctica (Krøyer) is described. The fine structure of the organ is found to agree with that of the oB among other investigated peracarideans. The difficulties met by Chaigneau in 1971 when homologizing the organs in B. arctica and in the Isopoda have been eliminated. Into the cavity of the oB, (probably) sensory neurones protrude. The perikarya of the neurones are found in the wall of the oB. On the dendrites there are subterminal dendritic swellings from which dendritic branches and cilia arise. The branching dendrites are characteristic of the oB in B. arctica. Also the cilia branch, thus increasing the amount of sensory membranes in the organ.