Gill ultrastructure and salinity tolerance of Caprella spp. (Crustacea: Amphipoda: Caprellidea) inhabiting the Sargassum community

The histology of the gill structure of Caprella (Amphipoda: Caprellidea) (i.e. C. danilevskii, C. subinermis, C. penantis R-type and C. verrucosa) collected from the Sargassum community of north-eastern Japan, was observed under transmission electron microscopy. The epithelial gill cells of C. danilevskii, C. subinermis, and C. verrucosa were composed of a well-developed apical infolding system (AIS) and basolateral infolding system (BIS) associated with a large number of mitochondria, whereas those of C. penantis R-type, which possessed large, leaf-like gills with distinct pillar structures, had weakly developed AIS and BIS. Experiments on the salinity tolerance of the four species of Caprella indicated that the median lethal concentration (LC50) of the four species at 20degreesC ranged from 12.97 to 18.84 practical salinity unit (p.s.u.) with survival rates greater than 80% in salinity conditions over 25.37 p.s.u. even on day 5. The characteristics of the gills and the wide salinity tolerance of Caprella spp. indicate that Caprella spp. inhabiting the Sargassum community are euryhaline marine organisms.