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Total surface area of the ion-permeable lamellar gills of Corophium volutator and Corophium curvispinum is 0·81 mm2mg-1 and 0·78 mm2mg-1 (wet weight), respectively. In both species, haemolymph flow (as visualized by haemocyte movements) is rapid through the peripheral canal and central luminal lacunae of each gill, general flow being from posterior to anterior margin of the gill. There appears to be countercurrent flow of haemolymph and ventilatory current water over the gill integument, which may facilitate dissolved-gas exchange.

Rate of haemolymph flow (perfusion) through the gills of the euryhaline C. volutator is markedly reduced immediately following transfer to a considerably hyperosmotic salinity (e.g. 15% S.W. to 85% S.W. transfer). No reduction in the rate of gill perfusion occurs following transfer of C. volutator to hypoosmotic salinity. The freshwater C. curvispinum does not tolerate hyperosmotic salinity transfers, but does exhibit a similar immediate gill perfusion restriction. The onset of gill perfusion restriction is dependent on a change in the magnitude of the ionic ([NaCl]), not the osmotic, gradient across the integument. In C. volutator only, normal rate of gill perfusion is eventually restored (within 24 hours of transfer), but can be immediately restored if the animal is transferred back to the acclimation salinity.

In C. volutator, branchial perfusion pattern is postulated to be regulated in relation to environmental salinity by a mechanism operating under neural control. The possible significance of gill perfusion restriction to C. volutator as a short-term adaptive osmoregulatory response is considered. Perfusion restriction in the gills of C. curvispinum is considered to be a relic of a recent estuarine ancestry.