MICROTUBULE SYSTEMS ASSOCIATED WITH THE SEPTATE JUNCTIONS OF THE GILLCELLS OF 4 GAMMARID AMPHIPODS

The microtubular systems associated with the septate junctions of the gill epithelial cells of four species of gammarid amphipod are describ ed, The four species examined included two relatively stenohaline mari ne forms, Chaetogammarus marinus and Gammarus locusta; a highly euryha line species, Gammarus duebeni, and a stenohaline freshwater species, Gammarus pulex, Of these amphipods, G. locusta and C. marinus maintain only a limited osmotic gradient between their haemolymph and the medi um and have a poorly developed junctional microtubular system; G. pule x has haemolymph which is some 300 mOsmol hypertonic to freshwater and has a well ordered system of microtubules on both sides of fairly lon g septate junctions; G. duebeni from brackish water tend to have a som ewhat shorter length of septate junctions lined by one or occasionally by a double row of microtubules, The most complex junctional microtub ular systems are shown by specimens of the freshwater race of G. duebe ni celticus which have been acclimated to seawater, These can take the form of multiple arrays in which some microtubules are linked to the plasma membrane by dense strands, It is suggested that these findings are consistent with the hypothesis that one role of these microtubules is to provide mechanical stability to enable the integrity of the sep tate junctions to be maintained during osmotic stress,