The main purpose of the study, based on the river continuum concept (Vannote et al.,1980), was to examine longitudinal structure, diversity, and functional organisation (functional feeding groups-FFG) of benthic communities in relation to system productivity, dynamics of particulate organic matter, and hydrological gradients of the whole catchment along with habitat heterogenity. Patterns in invertebrate community were determined in the submountain river Stradomka (Poland). Such studies are very rare, especially in Europe. Net daily production of benthic communities was negative and the heterotrophic processes prevailed. Gross production was positively related to PAR and PO4 concentration. The 3 groups DIPTERA, TRICHOPTERA, and EPHEMEROPTERA were the taxonomically most abundant. The highest taxon richness was found in the second stream order-67 taxa. In all seasons, habitats, and stream orders, the highest densities were indicated by dipteran and mayflies. Only 12% of the total 118 determined taxa in the catchment were present in all stream orders. Again, 29 taxa were restricted to headwater streams and 36 others to downstream sections. Longitudinal succession of species replacement was found for the 3 genera. Faunal density ranged widely, especially in the 3-4 orders (over 60 thousand individuals per square meter) however it usually was about 10 thousand individuals per square meter. Seasonally, the lowest benthic fauna density occurred in summer, and the highest in autumn and spring. Annual distribution of benthic fauna density in relation to stream order showed an exponential relationship. The highest biomass was observed in the fourth stream order. Average density and biomass were higher in winter than in summer. Densities of bottom fauna differed between habitats. Their highest values were found in riffles. At most river stations collectors dominated by density, however in the upstream sections shredders prevailed. Based on biomass a marked patterns of FFG distribution were estabilished for: collectors, feeding filters, and predators that dominated in the middle and downstream river parts; scrapers and shredders prevailed in headwater reaches; facultative group of collector/scrapers in the middle part. There is still little information on FFG biomass of benthic fauna in the context of their longitudinal distribution. Analysis of longitudinal distribution of FFG showed that shredders and scrapers were replaced by collectors, and again a set of 2 FFG (predators and shredders) were followed by filtrators along downstream direction. These shifts in functional fauna organisation have not been so far documented by other authors with the use of FFG biomass. However diversity of bottom community in lotic habitats was a little greater than in pools. Diversity did not correlate with the stream order. Longitudinal changes in functional organisation of benthos were better explained by faunal biomass. According to deterministic model of RCC and presented results, changes in stream morphology, abiotic parameters of the stream water and changes in riparian canopy development in Stradomka Catchment implied a specific functioning of benthic fauna communities. Observed changes along river gradient indicated a decrease of shredders that depended on coarse particulate organic matter, an increase of collectors and filter feeders which were based on fine detritus and suspended seston. The presented results confirmed most of tenets predicted by the RCC.