Zambezi Basin Wetlands Volume II : Chapters 7 - 11 - Contents i Back to links page CONTENTS VOLUME II Technical Reviews Page CHAPTER 7 : FRESHWATER FISHES .............................. 393 7.1 Introduction .................................................................... 393 7.2 The origin and zoogeography of Zambezian fishes ....... 393 7.3 Ichthyological regions of the Zambezi .......................... 404 7.4 Threats to biodiversity ................................................... 416 7.5 Wetlands of special interest .......................................... 432 7.6 Conservation and future directions ............................... 440 7.7 References ..................................................................... 443 TABLE 7.2: The fishes of the Zambezi River system .............. 449 APPENDIX 7.1 : Zambezi Delta Survey .................................. 461 CHAPTER 8 : FRESHWATER MOLLUSCS ................... 487 8.1 Introduction ................................................................. 487 8.2 Literature review ......................................................... 488 8.3 The Zambezi River basin ............................................ 489 8.4 The Molluscan fauna .................................................. 491 8.5 Biogeography ............................................................... 508 8.6 Biomphalaria, Bulinis and Schistosomiasis ................ 515 8.7 Conservation ................................................................ 516 8.8 Further investigations .................................................. 517 8.9 Conclusions ................................................................. 521 8.10 Acknowledgments ....................................................... 522 8.11 References ................................................................... 522 TABLE 8.1 : Systematic checklist of the freshwater molluscs found in the Zambezi Basin ............................ 493 ii Zambezi Basin Wetlands Volume II : Chapters 7 - 11 -Contents Back to links page CONTENTS (cont’d) VOLUME II Technical Reviews Page CHAPTER 9 : ODONATA ................................................... 527 9.1 Introduction ................................................................... 527 9.2 Previous work ................................................................ 529 9.3 Life cycle ..................................................................... 529 9.4 Conservation and potential threats .............................. 529 9.5 Areas of high species richness ..................................... 531 9.6 Gaps in knowledge and future research ....................... 532 9.7 References .................................................................... 532 9.8 Checklist and ecological notes ..................................... 539 TABLE 9.1 : Distribution of Zambezi Basin Odonata ............. 533 APPENDICES ........................................................................ 557 Appendix 9.1 : Barotseland - list of Odonata ........................... 557 Appendix 9.2 : Zambezi Delta Odonata ................................... 559 CHAPTER 10 : WETLAND LEPIDOPTERA .................. 565 10.1 Introduction ................................................................. 565 10.2 Higher classification ................................................. 566 10.3 Existing information ................................................... 566 10.4 Zambezi faunal regions ............................................. 567 10.5 Wetland species ......................................................... 574 10.6 Discussion .................................................................... 581 10.7 Conclusions ................................................................. 584 10.8 References .................................................................... 585 TABLE 10.1 List of species and subspecies from various butterfly families or subfamilies recorded from various parts of the Zambezi ......................... 587 APPENDICES .......................................................................... 601 Appendix 10.1 : Barotseland survey .... .................................... 601 Appendix 10.2 : Zambezi Delta survey .................................... 603 Zambezi Basin Wetlands Volume II : Chapters 7 - 11 - Contents iii Back to links page CONTENTS (cont’d) VOLUME II Technical Reviews Page CHAPTER 11 : AQUATIC INVERTEBRATES .............. 613 11.1 Introduction ................................................................. 613 11.2 Invertebrate groups .................................................. 614 11.3 Conservation .......... ................................................... 633 11.4 Conclusions and recommendations ............................ 635 11.5 References ................................................................... 638 TABLE 11.5 : State of knowledge about the major invertebrate groups in the Zambezi Basin .......................... 636 Zambezi Basin Wetlands Volume II : Chapter 8 - Review of Freshwater Molluscs 487 Back to Contents CHAPTER 8 FRESHWATER MOLLUSCS OF THE ZAMBEZI RIVER BASIN Cornell Dudley 8.1 INTRODUCTION The Zambezi River, its tributaries and wetlands make up one of Southern Africa's most important natural resources. Given the rapid rate of development and population growth in this region there is intensifying pressure on these resources. As a consequence, the river's wetlands and their associated biodiversity are under increasing threat. In order to more formally evaluate these resources, IUCN-ROSA, in conjunction with the Canadian International Development Agency, initiated the Zambezi Basin Wetlands Conservation and Resource Utilisation Project in 1996. This project is aimed at ensuring the wise use of the natural resources of the wetlands of the Zambezi Basin, focussing in particular on four project sites – the Barotse floodplains, the floodplains and swamps of the Chobe/Caprivi region, the wetlands of the Lower Shire Valley and the Zambezi Delta. One of the project activities is to evaluate the importance of biodiversity from a conservation perspective, both for the four wetland areas and for the wetlands of the basin as a whole. As part of this project technical reviews on the distribution, biogeography, ecology, importance, conservation interest and status of selected biological groups are required, of which this review of the basin's freshwater molluscs forms part. The freshwater molluscs are examined from both biodiversity and biogeographical perspectives. A analysis of the fauna is presented and checklists of the basin are included. In particular, the basin's centre of biodiversity, Lake Malawi, is compared with Lake Tanganyika, and the molluscs of the river basin are discussed in relation to the other major river basins of the continent – the Congo, the Nile and the Niger. Conservation aspects are evaluated and suggestions for future investigations are presented. Also included is a discussion of the distribution and importance of the genera Biomphalaria and Bulinus, intermediate hosts of Schistosoma species, which are important blood flukes of man. In most cases it is not difficult to define ecological limits for freshwater molluscs. Problems arise when coastal streams, estuaries and lagoons are considered, as a few species occupy both brackish and freshwater habitats, e.g. streams flowing into mangrove swamps, or near tidal influences. A few such species have been included in this review. Almost all mollusc families living in freshwater are, from a geological point of view, old families, possibly dating from before the Mesozoic era. Consequently they are of world wide distribution (Danish Bilharziasis Laboratory 1998). Gastropod (snails) classification is in a continuing state of revision and it will be some time before a system comes to be generally agreed for the groups of higher rank (Brown 1994). The freshwater bivalves (mussels, clams) have been a neglected group as they are of little economic or medical importance. Their systematics are even more difficult as species show great variation in morphology with relatively few constant characters. It is easy to recognise families but generic recognition often entails anatomical examination. Without sufficient experience of the family and country of origin, defining a species is often very difficult, and occasionally impossible (Danish Bilharziasis Laboratory 1998, Mandahl-Barth 1988). 488 Zambezi Basin Wetlands Volume II : Chapter 8 - Review of Freshwater Molluscs The Gastropoda, or snails, are commonly divided into two major subclasses, the Streptoneura (including the Prosobranchia) and the Euthyneura (including the Pulmonata). Prosobranchs have a comb-like gill (branchia/ctenidia) situated in the mantle cavity in front of the heart and are entirely aquatic. Attached to the foot is a horny or calcareous operculum which can be used to close the shell aperture. Sexes are separate. The group is most varied in the larger lakes and rivers of the continent and may contribute a major part of the invertebrate benthos biomass (Leveque 1972 in Brown 1994, Machena & Kautsky 1988). Species may be found to depths of 150-200 m. Pulmonates include terrestrial as well as aquatic species and have a mantle cavity serving as a lung. No gills are present although planorbid species have a gill-like respiratory organ in the mantle cavity called the pseudobranch. An operculum is lacking. Individuals are hermaphroditic. Pulmonates are most abundant in shallower ( 10 m) smaller water bodies,