Hydrobiologia The International Journal on Limnology and Marine Sciences Contents Volume 397 Opinion Taxonomy and biodiversity by K. Martens & M. Hamer Neodiaphanosoma a new genus of Sididae (Branchiopoda, Ctenopoda); with description of N. berga- mini sp. n. and comments on N. volzi (Stingelin 1905) by J.C. Paggi & C.E.F. da Rocha Taxonomy and morphology of limnic microturbellarians (Plathelminthes) in Extremadura (Spain) by C. Norefia, A. del Campo & M. del Real First data on an Index of Biotic Integrity (IBI) based on fish assemblages for the assessment of the impact of deforestation in a tropical West African river system by A. Kamdem Toham & G.G. Teugels Microlaimidae (Microlaimoidea: Nematoda) from the Indian Ocean: description of nine new and known species by A.W. Muthumbi & M. Vincx Seasonal and spatial changes in the sediment organic matter of a semi-enclosed marine system (W-Mediterranean Sea) by A. Pusceddu, G. Sara, M. Armeni, M. Fabiano & A. Mazzola 59-70 Environmental factors associated with the distribution of Simulium perflavum (Diptera: Simultidae) among streams in Brazilian Amazonia by N. Hamada & J.W. McCreadie 71-78 A generic index of diatom assemblages as bioindicator of pollution in the Keelung River of Taiwan by J.-T. Wu 79-87 Rare earth elements and heavy metal distribution in estuarine sediments of east coast of India 89-99 by R. Ramesh, A.L. Ramanathan, R.A. James, V. Subramanian, $.B. Jacobsen & H.D. Holland Variation in rostral dentition and telson setation in a saltmarsh population of Palaemonetes varians (Leach) (Crustacea: Decapoda: Palaemonidae) by S. De Grave 101-108 Toxic algae and fish mortality in a brackish-water lake in Aland, SW Finland by T. Lindholm, P. Ohman, K. Kurki-Helasmo, B. Kincaid & J. Meriluoto 109-120 Chironomid assemblage of a Lower-Rhéne dike field: relationships between substratum and biodiversity by E. Franquet 121-131 Three new species of Apheviderulix gen. nov. and proposal of Apheviderulicidae fam. nov. (Acari: Hydrachnidia: Eylaoidea) by R. Gerecke, I.M. Smith & D.R. Cook 133-147 1\ Evidence for an aquatic plant origin of ketones found in Taihu Lake sediments by Qu Wenchuan, M. Dickman, Wang Sumin, Wu Ruijin, Zhang Pingzhong & Chen Jianfa ... 149-154 Nematodes as indicators of pollution: a case study from the Swartkops River system, South Africa by T.K. Gyedu-Ababio, J.P. Furstenberg, D. Baird & A. Vanreusel 155-169 Relationships between trematode infection and habitat depth in a freshwater snail, Semisulcospira libertina (Gould) by K. Shinagawa, M. Urabe & M. Nagoshi 171-178 Driftwood: an alternative habitat for macroinvertebrates in a large desert river by G.A. Haden, D.W. Blinn, J.P. Shannon & K.P. Wilson 179-186 Trace metal concentrations in coastal marshes of the Lower Parana River and the Rio de la Plata Estuary by C. Villar, J. Stripeikis, M. Tudino, L. d’ Huicque, O. Troccoli & C. Bonetto 187-195 Meiobenthic arthropod communities in new streams in Glacier Bay National Park, Alaska by A.L. Robertson & A.M. Milner 197-209 Relationships between metals and hyporheic invertebrate community structure in a river recovering from metals contamination by S.M. Nelson & R.A. Roline 211-226 Periphyton biomass on Echinochloa polystachya (H.B.K.) Hitch. of a lake of the Lower Parana River floodplain, Argentina by H. Pizarro 227-239 Modelling advective transport of Ulva lactuca (L) in the sheltered bay, Mgllekrogen, Roskilde Fjord, Denmark by J. Salomonsen, M. Flindt, O. Geertz-Hansen & C. Johansen Book reviews Author Index