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INTEGRATION OF FRESHWATER BIODIVERSITY INTO ’S DEVELOPMENT PROCESS:

MOBILIZATION OF INFORMATION AND DEMONSTRATION SITES

Demonstration Project in the Gambia River Basin

Training of Trainers Module

on the

Monitoring of Freshwater Molluscs

Dr. Ndiaga THIAM & Anis DIALLO

September 2010

INTEGRATION OF FRESHWATER BIODIVERSITY INTO AFRICA’S DEVELOPMENT PROCESS:

MOBILIZATION OF INFORMATION AND DEMONSTRATION SITES

Demonstration Project in the Gambia River Basin

Training of Trainers Module on the

Monitoring of Freshwater Molluscs

Wetlands International Afrique Rue 111, Zone B, Villa No 39B BP 25581 DAKAR-FANN TEL. : (+221) 33 869 16 81 FAX : (221) 33 825 12 92 EMAIL : [email protected]

September 2010

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Contents

Introduction ...... 4 Goals and Objectives of the module ...... 5 Module Contents ...... 5 Training needs ...... 6 Course procedures ...... 6 Expected Results ...... 7 I.- Study area ...... 8 1.- Presentation of The Gambia River Basin ...... 8 2.- Ecobiological features of the Gambia River Basin ...... 10 3.- Bilogical diversity of molluscs in The Gambia River Basin ...... 11 II.- General points ...... 13 1.- Classification of molluscs ...... 13 2.- Morphology and anatomy ...... 19 III. Ecobiology ...... 27 1.- Geographical distribution of freshwater molluscs ...... Error! Bookmark not defined. 2.- Ecology ...... 29 3.- Resilience via anhydrobiosis ...... 30 4.- Habitats of freshwater molluscs ...... 31 5.- Reproduction ...... 32 IV. Importance of freshwater molluscs ...... 35 1.- Importance of freshwater ecosystems ...... 35 2.- Ecological relevance of freshwater ecosystems ...... 35 3.- Role of molluscs in the transmission of helminthiasis ...... 35 4.- Shellfish and marine pollution ...... 36 V.- Threats to freshwater ...... 37 VI.- Monitoring Protocol for molluscs in The Gambia River Basin ...... 38 1.- Equipment and methods ...... 38 Recommendations ...... 40 Bibliographic References ...... 41 Appendix ...... 42

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INTRODUCTION

Molluscs are found in most African freshwater environments. They can be distinguished from other aquatic species by the presence of a calcified one-piece shell as in gastropods and a two- piece shell in lamellibranchs (also called Pelecypoda or bivalves). Molluscs in general, and in particular pulmonates that play a central role in the transmission of human and parasitosis, have often been better studied than other invertebrates of the Sudanian region. Many taxonomic, biological and ecological issues however, have yet to be resolved.

The Gambia River Basin Development Organization (OMVG), which is composed of The Gambia, the Republic of Guinea, Guinea Bissau, and , plans to build a hydroelectric dam at the Sambangalou site. The construction of this dam will consequently disturb the biodiversity as evidenced by the impact studies conducted by OMVG. To mitigate the negative impacts of this project and, at the same time to try and improve the positive impacts, Wetlands International Africa has agreed to the implementation of a monitoring plan for the biodiversity of freshwater ecosystems in The Gambia River Basin. This project will be carried out in partnership with the IUCN-Species Survival Commission and the Organization for OMVG, through Phase 2 entitled “Demonstration Project of The Gambia River (West Africa)” as part of the program: “Integration of Freshwater Biodiversity into Africa’s Development Process: Mobilization of Information and Demonstration Sites”.

To this end, Wetlands International, in collaboration with its partners, is interested in developing this educational module on malacologic fauna, with the prospect of monitoring the Gambia River Basin. Thus, this module on freshwater molluscs has been created for trainers in the field of biodiversity monitoring, and especially after the opening of the Sambangalou dam, will be a part of the framework for the creation of an observatory.

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Objectives of the module

The module aims to:  Provide general information related to molluscs (, ecobiology, etc.)  Establish a monitoring memorandum for the biodiversity of molluscs

 Build trainers’ species monitoring

abilities for the preservation of Contents of the module specified biodiversity

 Appraise the didactic means and the

training period of targeted groups The module is comprised of six parts :

 Provide available information on the  Presentation of the study area potential impacts of the construction  General Points of the Sambangalou hydroelectric  Ecobiology dam  Importance of freshwater molluscs  Monitoring Protocol for freshwater molluscs

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Needs for this

Course procedures training

The didactic materials needed are as The 20 hours provided for this training are follows: divided as follows: - Maps of the local area and of - Introduction (1 hour) study sites - Presentation of the study area (2 h) - Plates for the identification of key - General points on crabs (5 h) species - Ecobiology (4 h) - Distribution maps of key species - The Importance of crabs (2 h) - Equipment necessary for - Threats to freshwater species (1 h) biodiversity monitoring - Monitoring protocol for crabs in the Gambia (illustration of the materials) River Basin (4 h) - Recommendations (1 h)

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Expected Results

Biodiversity monitoring will be conducted as follows: - Listing and maping of species - Defining the community structure of particular sites - Develop and understanding of spatiotemporal distribution of molluscs - Conduct comparative study of the specific composition upstream and donwstream of the dam - Note frequencies of species’ sizes - Undertake weight study of species

At the end of the training session, the future trainers will have mastered:  The biological and abiotic impacts caused by the construction of the dam  The methodological monitoring approach of the biological diversity of crabs  The ability to train other target groups to further the dissemination of the need for diversity preservation and the valorization of sampled resources

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I.- STUDY AREA

1. PRESENTATION OF THE GAMBIA RIVER BASIN

The Gambia River has its source in the high rainy mountains of Fouta Djallon in the northern central region of Guinea. The total amount of water flowing from Guinea to Senegal is estimated at 3 cubic kilometers per year. The river then flows northwards to extreme-eastern Gambia. The Gambia River Basin (Figure 1) spans 77,850km2. The flow of the River varies according to the rainy and dry seasons, between 2,000 and 10 cubic meters per second, respectively. For this reason, and because of the flat topography of The Gambia, the salt waters run up to 70km upstream during the rainy season and up to 250km upstream during the dry season. This has impacted the species distribution and the habitats at the river’s mouth. All variations in the river flow have an impact on the composition and structure of the areas near the river’s mouth. Three main types of swamps can be found in the basin, namely mangroves near the river’s mouth, small floodplains in the middle and thick riverside forests in the mountains of Guinea. These swamps provide habitats for roughly 1,500 species of , 80 species of mammals, 330 species of birds, 26 species of reptiles; about 150 species of freshwater fishes, and 481 additional species found in the coastal lagoons. Several endangered species such as chimpanzees, crocodiles and the Egyptian plover are still found in these regions. About 3 million people live in The Gambia River basin the majority of which are farmers (70-90% of the population). Other activities include fishing, raising livestock, forestry and trade. The Gambia River Basin Development Organization (OMVG) was founded in 1978 to foster the development of the basin in terms of irrigation and hydroelectric power. To meet the ever increasing need for clean energy, a feasibility study was conducted for the erection of a dam in the upper side of The Gambia River. The construction of a hydroelectric dam has recently been approved at a site near Sambangalou. The dam

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will have an impact on the hydrological, abiotic, and ecological features of the river. The main impacts are: • Reduction of the maximum flood flow by 50 to 60% • Reduction of the water depth overall by 10 cm on average • Intrusion of saline water to nearly 150 km, resulting in: - loss of animal biodiversity and mangroves along the river bank - possible changes in the morpho-sedimentary layout and microbiology - decrease in irrigation water levels - depletion of fish production

The dam will also have a significant impact on freshwater biodiversity, not only on commercial fish species, but also on endangered such as the West African manatee. As recommended in the assessment of environmental impacts, local communities shall be compensated for their loss of income resulting from environmental changes. Changes must be monitored continuously to identify any obvious alteration in biodiversity that requires a management response.

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Figure 1 : The Gambia River Basin

2. ECOBIOLOGICAL FEATURES OF THE GAMBIA RIVER BASIN

Five main types of bottoms were identified in The Gambia River Basin - rocky or stony bottoms, silt-laden, clayey, sandy, and lateritic bottoms. The rocky and stony bottoms are found in the biotopes with flowing water, particularly along the drainage line of The Gambia River and its tributaries. The clayey and silt-laden bottoms have mainly developed in the flood-prone zones. The lateritic soils are found in ponds. There are also clayey-silt laden, clayey-lateritic and sandy-clayey bottoms. Following the biotopes, we can roughly distinguish two populations of molluscs in stagnant water (ponds, basins) and in flowing water (torrents, streams). Some species can however live in either biotope. Stagnant water is the prefered living environment for pulmonary molluscs, as they generally have abundant vegetation. The population dynamics of molluscs are purportedly controlled by the rainfall, and by the dry and high water cycles of the watering places (Diaw,

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undated). Species belonging to the genera , Aspatharia and Biomphalaria survive this drying process.

3. BIOLOGICAL DIVERSITY OF MOLLUSCS IN THE GAMBIA RIVER BASIN

Some 38 species of molluscs (Annex 1) are divided into 25 genera and 15 families. The most diversified families are the having ten species, followed by the Mutelidae counting nine species. The most well represented is Bulinus (six species) of the Planorbidae family. It is worth noting that the list comprises species that are, in general, found in brackish environments. They are euryhaline species generally found in blackish waters, but which can live in freshwater near the coast. They have a distribution area limited to the coastal margins of the continent and could be termed peripheral dulcicoles in contrast to to the species that are essential dulcicoles, known as primary dulcicoles. Considering the difficulties of setting a sharp demarcation line between fresh and brackish waters in natural ecosystems, these species were mentioned nonetheless, on the list of encountered taxa. Furthermore, many species present in the freshwaters of the rivers of both Senegal and Guinea are not on the list, but are likely to be found in the basin of The Gambia River.

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Figure 2 : Variation in the number of freshwater molluscan species by family

Certain authors list species of the genus Bulinus in the Planorbidae family (like in figure 1 below). Others however distinguish the Bulinidae family.

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II. GENERAL POINTS

1. CLASSIFICATION OF MOLLUSCS

1.1 MOLLUSCS PLACE IN THE ANIMAL KINGDOM

The phylum is very large. They began as annelids and rapidly lost their segmentation. Of primary interest at the development level is the specialisation of organs, and the development of closer and closer links between these different organs (Table 1).

Table 1 : Position of Molluscs in the animal kingdom

♦ Echinoderms: Urchins, Unicellular procaryotes Crinoids, Sea ♦ Bivalves (shellfishes) (cell without nucleus) cucumbers, starfish and ophiurian. Unicellular Eucaryotes ♦ Gastropods (snails,

(cell with nucleus) , etc.) ♦ Sponges (multicellular ) ♦ Molluscs (cuttlefish, , ) Polyps: hydra, coral and jellyfish Worms (mobility and ♦ Trilobites (two to 24- digestive tract) legged - extinct) bilatarian ♦ Primitive Agnathous fishes ♦ Decapods: crabs and myriapods type (multi- (jawless) crayfishes (10-legged) legged) ♦ Arachnids : Spiders, Primitive fishes scorpions and acarians ♦ Dragonflies (cartilaginous fishes) (8-legged) Hexapods (6-legged) : Typical fishes (bony Insects of Apterygota ♦ Cockroaches, ♦ Snakes fishes) type (wingless primitive mantises, termites. ). Sarcopterygii fishes ♦ Orthoptera ♦ Dinosaurs (extinct) (with fleshy fins) (grasshopper, cricket). Primitive Tetrapods ♦ Hemiptera (bugs, ♦ Crocodiles ♦ Marsupials (Amphibians) cicada,...) Primitive Reptiles ♦ Insectivores (Mole, ♦Coleoptera beetles, ♦ Tortoises (Amniots/ Lizard type) Hedgehog,...) ladybugs,...) ♦ Hymenoptera (bee, ♦ Birds ♦ Chiroptera (Bats) wasp, ant) ♦ Primates ♦ Diptera (flies) Primitive Mammals ♦ Rodents and ♦ Lepidoptera (butterfly) monotreme type Lagomorphs (rabbits)

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♦ Carnivores ♦ Ongulates

1.2 PHYLUM MOLLUSCA

Phylum Mollusca (Table 1) was designated by Georges Cuvier (1769-1832) in 1795. Molluscs (from Latin mollis, "soft") are a branch of the animal kingdom, with over 130,000 freshwater species. Eight classes of molluscs have been identified: • Solenogasters (350 known species living in deep seas) • Caudofoveata (100 known species living in oceans worldwide) • Polyplacophora (900 known species living at depths between 0 and 3000 m) • Monoplacophora (15 known species living in ocean trenches) • Gastropods (103,000 known species found worldwide) • Cephalopods (786 known marine species, living in all seas except in the Black Sea) • Bivalves (12,000 species living in freshwater and oceans worldwide) • Scaphopoda (400 marine species)

Solenogasters and Caudofoveata were formerly grouped in the same class of Aplacophora. Instead, eumolluscs include all molluscs except Solenogasters and Caudofoveata. Conchiferes form a subbranch including all eumolluscs except Polyplacophora. Amphineura are the second subbranch of Molluscs and group Aplacophora and Polyplacophora. Bivalves and Scaphopoda can be grouped as “Diasomes”.

Table 2: Definition of classes of molluscs

Monoplacophorans One-pieced shell. Presence of metameres. (Neopilina – single existing species)

Aplacophorans Neither shell nor plate (but the larva has 8), the (Neomia) tegument contains spicules.

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Polyplacophorans Presence of 8 jointed plates arranged in a series from (Chitons) front to back

Gastropods Spiral shell around an imaginary axis. (snails)

Scaphopods Single coned shell slightly arched, open at both ends. (tusk shells) Smaller heads

Lamellibranchs (either bivalves or headless) Shell with two separate but hinged valves. Headless. (Oysters, mussels ...)

Cephalopods Shell can be inner and smaller. Presences of tentacles. (Cuttlefish, octopus)

Figure 3 : Polyplacophora (Chiton olivaceus, C. corallinus)

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Figure 4: Scaphopode (Dentalium sp)

Figure 5 : Gasteropods (Bolma rugoso, Monodonta turbinata, Patella ferrugina)

Figure 6: Lamellibranchs (Mytilus edulis, Glycymeris pilosa, Crassostrea gigas)

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Figure 7: Cephalopods (cuttlefish, octopus, squid)

1.3 TAXONOMY OF FRESHWATER MOLLUSCS

Freshwater molluscs are represented in Sudanian Africa by gastropods (one-pieced shell) and lamellibranchs (shell with two hinged valves). Only truly aquatic species have been included in the key below. One can however, encounter two non-aquatic genera (Succinae and Veronicella) living in close proximity to water. Succinae have a shell shaped like Lymnaea’s but the two genera are distinguished by the position of their eyes. Succinae have their eyes perched on their hind tentacles while

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Lymnaea and aquatic pulmonary genera have theirs placed at the base of their tentacles. Succinae also have larger feet. Veronicella have no outer shell and look like slugs. The classification of aquatic molluscs is outlined in Table 3.

Table 3: Classification of Molluscs

Molluscs Class Pelecypoda Subclass Prosobranch Order Mesogastropoda Basommatophora Eulamellibranch Suborder Schizodonta Heterodonta Familly Pilidae Ancylidae Unionidae Corbiculidae Planorbidae Mutelidae Sphaeridae Bulinidae Bythinidae Lymnaeidae

According to the shape of the shell and a few common anatomical features, it is relatively easy to determine the family and the genus of most molluscs found in Sudanian Africa. The distinction of species in contrast, is often difficult within many genera. In effect, due to the limited possibilities of dispersion and the absence of interaction amongst basins and collections of water, these molluscs could likely represent populations that have evolved in genetic isolation. The greater the period of isolation, the greater the probability that one finds a local variety that differs genetically from the typical form of the species. Molluscs are also equally sensitive to the environmental conditions in which they live. Thus, the calcium content of water will determine the thickness of their shells, and if ecological conditions are ideal, the animals can reach sizes much larger than if they were in less favorable environments. Lastly, amongst the Lamellibranchs Unionidae and Mutelidae for example, the general shape of their shell can vary considerably from one habitat to another, while in the same hydrological basin. It is easily understood that the increase in ecophenotypes associated with variations in genetic evolution, makes it difficult to identify specific molluscs. The task is further complicated, given the fact that many diagnoses have been conducted with unique

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specimens that are sometimes in poor condition. Other issues tie in to the fact that the descriptions are often cursory and that some types of specimens have either disappeared or are unusable (atypical, eroded shells, etc.).

All of which serves to explain the possible divergent opinions among experts at this specific level. In pulmonates, also bilharzias carriers, which are by far the most studied in Africa, all the possible anatomic features were meticulously examined. Despite this, some doubts remain. New techniques (chromatography, study of chromosomes) currently used still fail to solve the problems, and in some cases tend to complicate them.

Much remains to be done at the taxonomic level and the synthetic work is still nonexistent, with the exclusion of pulmonates. We cannot overemphasize the immediate importance of regional studies, basin by basin for example, and the harvest of many molluscs in series and of various sizes, including young stages; especially amongst the bivalves. In fact, these series can enable a statistical study of individual variations, according to age. They are essential to all relevant studies of Unionidae and Mutelidae (Aspatharia and Spathopsis in particular).

2. MORPHOLOGY AND ANATOMY

2.1. GENERAL FEATURES

Phylum Mollusca draws its name from the Latin mollis “soft”. The scientific study of molluscs is called Malacology.

Despite the great diversity of forms, several characteristics are found in all living molluscs. The dorsal part of the body is a secreting calcareous spicules, forming plates or a shell. Between the mantle and the visceral mass is located the mantle cavity from which open the anus and genital ducts. The nervous system has a nerve ring around the esophagus with at least two pairs of nerve cords (three in bivalves).

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Most molluscs have lost all traces of metamerisation. They have a bilateral symmetry which can however be altered by the twisting of the body. They have a soft tegument which has many mucus-secreting glands.

Molluscs are coelomate, but their coelom is limited to a pericardium, that is to say the heart is located in a cavity of tissue of mesodermal origin. The general cavity of molluscs is more or less obliterated by a connective tissue, with the exception of the portion surrounding the heart (pericardium) and another portion, in connection with the other two, which constitutes the excretory organs (nephridia).

GASTROPODS Gastropods have one-pieced shells for the protection of the animal's body. This soft and segmented animal has three major parts:

- The head has a pair of contractile tentacles bearing eyes at their terminus, in aquatic snails. In general, the mouth contains a chitinous jaw on the dorsal side and a (a scraping organ for mastication in certain molluscs) on the ventral side.

- The foot is a muscular organ is often well-developed for locomotion.

- The visceral mass is covered in a membrane called the mantle, which secretes the shell. The visceral mass contains the major organs. Gastropods have a mantle cavity formed by a fold of the mantle, opening to the anus and urinary orifice. The mantle cavity contains a gill in prosobranchs. Lamellibranchs have no gills but they have a lung cavity with a vascular roof.

Figure 8: Gastropod (snail)

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LAMELLIBRANCHS The shell of bivalves is composed of two hinged valves which are joined by a ligament. They are anatomically distinguished from gastropods by the absence of individual heads; hence they are called “Acephales” the name by which their group is often distinguished. They have neither jaw nor radula, and their mouth, lined with four ciliated palps, opens straight into the esophagus. The muscular foot is compressed and tongue-shaped and mainly enables the animal to burrow into the sediment. Two folds of the mantle delineate the mantle cavity wherein lie the gills. At the extreme posterior of the animal, the edges of the mantle may be partially fused. They can also delineate exhaling and inhaling orifices, that sometimes extend into tubes or siphons.

Figure 9: Lamellibranchs (bivalve)

2.2 FOCUS ON THE SHELL

The French word for shell “coquille” derives from classic Latin “conchylium”. This word came from ancient Greek and referred to hard limestone shells, whether of eggs or snails. In French, this word was used even in the late nineteenth century for the shells of crayfish. Nowadays, though this word has a more limited sense, it still has many homonyms. In the French vernacular, this word refers to some species directly, such as scallops, or butterfly shells, while some use words derived directly such as hulls. If the shell becomes detached from the animal that secreted it, it is commonly called a shell.

The shell (or test) of molluscs contains calcium carbonate (calcite and aragonite). It is secreted by the mantle as the animal grows. Living molluscs have their shells covered with a thin dog-eared layer of a substance (conchiolin) called , that protects the limestone layers. The interior of the shell is covered with a satin-smooth layer of .

Gastropods’ one-pieced shell results schematically from the coiling of a very elongated cone around an axis called . This is called a dextral shell when the cone coils clockwise, if viewed from the apical pole (or ). If the cone coils counterclockwise, it is called a sinistral shell (Figure 10). Except for Ancylidae, the shell has several turns of whorls separated by sutures. The or is bordered by a (or labrum). In prosobranchs, the , which is a chitinous or calcified piece at the foot of the animal, closes up the peristome when the animal retracts. Only pulmonates have such a piece.

Figure 10 : (1) Sinistral shellfish (Bilunus) of Gastropod, a: apex, l: labrum, p: peristome; s: sp: . (2) Dextral shell (Lymnaea) of gastropod.

Bivalves (Figure 11) have shells with two -often symmetrical- valves. On the dorsal edge of each , there is a more or less prominent top/crest called hook or umbo, below which is the hinge. The latter, which allows the articulation of valves, is a gearing device more or less complicated, with teeth that penetrate into the cavities of the other valve. Near the top, and outside the shell, there is a spindle-shaped ligament consisting of conchiolin. It keeps the valves interlinked and allows their separation because of its inherent elasticity. On the

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opposite side from the dorsal edge, lies the ventral edge from which the foot of the animal can draw out. The front edge is near the mouth, while the hind edge, on the opposite side, is close to the siphons. On the closed shell, the hook bends toward the front edge. The adductor muscles enable the valves to close up, as they are perpendicularly slot in the inner side of valves. While studying shells, some measurements were made.

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Figure 11: Left valve of pelecypods (Coelatura) cr: hook, dc: cardinal teeth; dla: anterior lateral teeth; dlp: posterior lateral teeth; l: ligament; Maa: anterior adductor muscle scar, map: adductor muscle scar Posterior mpp: protracteur anterior muscle of the foot; mra: footprint of the anterior foot retractor muscle; mrp: footprint of the posterior retractor muscle of the foot.

The most common is the height of the shell in gastropods, or the diameter when the coiling occurs in a plan, as with Planorbidae.

In Lamellibranchs, the length and height are respectively the biggest dimensions in the anterior-posterior and vertical directions while the thickness is the biggest transversal dimension.

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2.3 RADULA

The radula is located on the ventral side of the mouth. It is a chitinous ribbon-like structure covered with rows of many small, transverse teeth on the dorsal side. Each row is comprised of a central tooth with lateral and marginal teeth symmetrically lining both sides. The number of teeth may depend on the age of the animal. Adult Biomphalaria (Planorbidae) have a number of teeth that can vary between 39 and 59 in each row, while prosobranch molluscs usually have less than seven. The shape and arrangement of teeth have a systematic value, especially in pulmonates. The central tooth of these pulmonates has two cusps, and lateral teeth have three main cusps called the endocone, mesocone and ectocone. The endocones can stand divided into two or more cusps, whereas the mesocone and ectocone are rarely divided on the lateral teeth. The marginal teeth are long and arranged slantwise. The endocones, and sometimes the ectocones, are divided into many secondary cusps.

2.4 NERVOUS SYSTEM

The nervous system typical of molluscs has cerebral ganglia (that can merge to form the brain) interconnected to pedal and visceral ganglia by a double esophageal ring.

2.5 CIRCULATORY SYSTEM

Circulation is open and incomplete. The animal has short arteries rooted on the heart but has neither veins nor capillaries. The blood is either colorless or slightly colored by dissolved hemoglobin or hemocyanin.

2.6 REPRODUCTIVE ORGANS

In molluscs, sexes are usually separate. The eggs are more or less rich in vitellin, and hatching takes place after a somewhat advanced stage of development. The free larva (, ) looks much like the of annelids. In pulmonates, some species can be distinguished by the morphology of the genital organ and especially of the reproductive organ.

Planorbidae’s genital organ has a hermaphroditic genital gland (ovotestis) large enough that it extends through a hermaphroditic duct with several seminal vesicles on its upper side. This

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duct in turn divides into a male part (sperm duct) and a female duct, one formed by the oviduct and the albumen gland. The distal oviduct (uterus) opens into the vagina, which in turn opens below the mantle’s edge on the animal’s left side. The spermatic duct is extended by a vas deferens to the reproductive organ. It comprises a sheath surrounding the penis in its upper part, and by a broader prepuce in its lower part. The reproductive organ opens below the left tentacle of sinistral shelled-molluscs, and below the right tentacle of molluscs with dextral-coiling shells. The shape of the reproductive organ and the relative proportions of the sheath and prepuce, are used in taxonomy. Some species called “aphallic” may have no reproductive organ. Pulmonates have a retractile reproductive organ while prosobranch’s is non-retractile. In the latter group, Thiaridae have no such an organ whereas Bythinidae have a well developed one. Viviparidae’s right tentacle is transformed into a reproductive organ.

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III. ECOBIOLOGY

1. GEOGRAPHIC DISTRIBUTION OF FRESHWATER MOLLUSCS

Most aquatic molluscs from the Sudanian zone have a wide geographical distribution that often goes beyond the scope of the study area. Cases of endemism are rare and it is often boring to map the distribution of any species because of the numerous synonyms either acknowledged or simply presumed by authors.

This is especially true among certain Lamellibranchs for which the concept of species is sometimes subjective, because there are no accepted criteria.

1.1. PROSOBRANCHS

Pilidae: Pila genus has been reviewed by Pain (1961) and three species can be found in the Sudanian zone: P. wernei (from Egypt to Niger, Congo and ).

Four lanista species are identified: L. ovum (Nile Basin, Chad Basin, Nigeria, and Angola), L. guinaicus (Niger, Volta, Senegal Basins; Cote d’Ivoire and Dahomey Rivers), L. adansoni (Senegambia) and L. lybicus (West Africa).

Viviparidae: unicolor are found throughout Ethiopia, and many species described from different parts of Africa are possibly synonymous. B. Duponti are spotted in Senegal.

Tharidae: Melania fuberculata are present in most of African regions, except in the Niger and Congo Basins. These species are also found in the Arabian Peninsula and Asia. Cleopatra bulimoides exist all across Ethiopia. As for B. unicolor, other species described in this region are possibly synonymous. Pofadoma are present only in the coastal Gulf of Guinea (from Liberia to Congo) and in the eastern basin of Congo.

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Most species live in forest streams and they are occasionally found outside these areas. However, they may swim upstream to the Sudanian zone in gallery forests along rivers.

Bithynidae species: They generally have a more restricted geographical distribution than the previous ones. Gabielle tchadiensis are spotted in Lake Chad, and G. senaariensis are found in Egypt, Sudan and Chad. G. adspersa and Jubaïa aethiopica are present in Ethiopia while Bithynia tournieri are located in Cote d'Ivoire.

1.2 PULMONATES

Lymnaeidae: Lymnaea natalensis are the only widely distributed species of the genus in Africa. Bulinidae: Bulinus globosus, B. forskali and B. truncatus are found throughout Sub Saharan Africa. B. jousseaumei are present in The Senegambia, Niger and Chad Basins. B. sericinus and B. abyssinicus exist in Ethiopia while B. obtususare are found in Chad. In West Africa, there are B. guernei, B. senegalensis (Senegambia, Niger, Chad), and B. umbilicatus (Mali, Mauritania, Sudan).

Planorbidae: many species and subspecies in Africa have been identified in the Biomphalaria genus. B. alexandrina are limited in the Nile, B. sudanica are spotted in East Africa and the Chad Basin, and B. pfeifferi comprise several subspecies distributed throughout Sub-Saharan Africa. Ceratophalus natalensis (e.g. natalensis) Afrogyrus coretus (e.g. Anisus coretus) Gyraulus costulatus and Segmentina angustus are widely distributed in Africa. Gyraulus bicarinafus are found in Lake Chad, Ethiopia and Uganda whereas Afrogyrus oasiensis are present in Egypt.

1.3 LAMELLIBRANCHS

Mutelidae: Mutel dubia (synonyms: M. angustata, etc..) and M. rostrata are common species with wide geographical distribution beyond the Sudanian area. M. Joubin, which is rarer, is reported in the Niger and Chad Basins. M. Francis has been described in the Middle Niger and M. nilotica in the Nile Basin. Spathopsis Rubens is widely distributed in the Sudanian zone. S. Bellamia is known in Niger and Cote d'Ivoire while S. adansoni is known in the Senegal Basin. As for the Aspatharia genus, even more than the previous ones, the specific

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determination is far from being easy, and any attempt at a geographic distributional distinction is questionable. A. dahomeyensis (and related forms) seems widespread, as well as A. chaiziana. Several other species were reported from West Africa (A. Tamai, rochebrunei, pangallensis, mabillei, tritis, nigeriensis, senegalensis and complanata).

Unionidae: Caelatura teretiuscula is known in the Chad Basin and in the Nile. C. aegyptiaca and its various forms are found throughout the area. C. Aequatoria has been reported in Niger and C. mesafricana in Senegal.

Corbiculidae: Corbicula africana appears to be widely distributed in Niger.

Sphaeridae: Pisidium Piroth, which is known in Chad, is apparently the only Sphaerium Courtet species to also found in Chad, Cote d'Ivoire while Eupera parasitica is widely distributed in Africa.

Etheridae: Etheria elliptica has a wide distribution in Africa (in the Nile Basin and in Senegal).

2. ECOLOGY

There is a rough distinction between populations of molluscs in stagnant water from those in flowing water, though some species live in either. Except bilharzias-vector pulmonates, studies on the ecology of freshwater molluscs are rare in Sudanian Africa.

In stagnant water, pulmonates are generally dominant and are often abundant in vegetation. Ceratophyllum-type seagrass beds usually hosts a rich fauna, in majority Bulinus, Biomphalaria, Lymnaea, Gyraulus, Segmentina, Afrogyrus, Ceratophallus, associated with Prosobranchia Gabbia and Pila (Leveque, 1975). In some places, Ceratophyllum-type seagrass beds seem to be most appropriate for Pulmonates. Potamogeton and Valisneria- type seagrass beds home a less rich fauna. Pulmonates are also common on all fragments floating near shores.

However, prosobranchs (Melania, Bellamia, and Cleopatra) are dominant on the bottoms and are associated with small bivalves (Corbicula, Pisidium, Eupera) and Unionidae (Caelatura). The density and species occurrence is often relative to environmental aspects in the area,

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including salinity and the nature of the bottom play an extremely important role (Leveque, 1972). Prosobranchs live in surface sediment or are slightly buried when the substrate is very loose.

In temporary water holes, the malacofauna, which are also often composed of Bulinus, and sometimes of Biomphalaria, are always quite limited.

In general, flowing waters are home to big Lamellibranchs (Mutelidae). One of the most frequent is Etheria elliptica that lives attached to solid substrates (rocks, logs, etc...) or in colonies there are no substrates. Aspatharia, Spathopsis and Mutela live embedded slantwise in the sediments, exposing only their siphons. They filter the water to extract algae, plankton and fragments to feed on. Caelatura are also common in these environments, as well as Eupera, live attached to rocks or plants.

Wildlife in stagnant waters can be found midstream or in quiet areas near the edge or in basins when water levels are low. Nevertheless, some Biornphalaria are likely to live in flowing water.

3. RESILIENCE VIA ANHYDROBIOSIS

Temporary aquatic environments are common in the Sudanian zone (rainy season pools, floodplains, etc...) and populating molluscs are particularly resilient to drying and dehydration. For example, Bulinus senegalensis molluscs sink into the bottom mud when the pond dries up and are able to withstand the harsh conditions of the dry season, either as adults that hibernate underground secreting a barrier-like protection (adults) or by erecting a spawning-like hedge resistant to drying (Gretillat,1961).

For six months, Daget (1961) kept some Spathosis Rubens species on the table in his laboratory and weighed them regularly. Afterwards, he noted the existence of a 20-day adaptation phase in anhydrobiosis, with a fast weight loss. He then noted in the anhydrobiosis phase a much slower weight loss. Six months later, the five specimens studied revived shortly after being released into water. The shells half-opened within half an hour to one hour. The same author (1962) further noted that in Aspatharia put for 13 months in such conditions, the percentage of surviving individuals was 86% in Aspatharia Tritis, 32% in A. mabillei and 5%

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in A. complanata and A. rochebrunei. Resilience through anhydrobiosis, exhibited by these big lamellibranchs, allows them to colonize rivers that dry out temporarily.

Many pulmonate molluscs can also hibernate. Larivibre and al. (1962) showed in the laboratory that Bulinus guernei burrow underground while Biomphalaria pfeifferi remain on the surface. After one month, 100% of B. guernei survived desiccation against only 50% of B. pfeifferi. Chu and al. (1966) also observed that Bulinus truncatus burrow into the soil to resist desiccation. For this species, the survival rate is higher in young individuals than in adults. can live more than 6 months in an anhydrobiotic state. After hibernation, Pulmonates seem to resume normal life with a biological activity greater than other common individuals. Thus, Chu and al. (1967) showed that after drying, the spawning of B. truncatus was two times higher than normal. On the other hand, Leveque (1968) found that B. forskalii following anhydrobiosis grew more rapidly and reached a larger size.

4. HABITATS OF FRESHWATER MOLLUSCS

Freshwater habitats cover less than 1% of the land surface and yet contain over 25% of all vertebrates described, over 126, 000 species and nearly 2,600 macrophytes.

Various types of habitats are prone to host molluscs such as a minor riverbed, floodplains, tributaries, and ponds. The presence, distribution and abundance of freshwater molluscs depend on the characteristic features of the milieu, among them the salt content, vegetation, and nature of the bottoms that play such a crucial role. Vegetation and bottoms represent the main habitats for molluscs. The characteristic habitats may vary, according to species groups. Pulmonates are common in aquatic vegetation. Posobranchs and bivalve molluscs dominate the bottoms.

Some species of freshwater molluscs have the remarkable ability to withstand drought and live in an anhydrobiotic state. This means that, following desiccation of the environment they

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live in a state of slowed animation and remain in this state until the return of favourable conditions.

5. REPRODUCTION

The gametes come out through the genital ducts in the mantle cavity. After fertilization, the egg undergoes spiral segmentation, forming a trochophore larva as in annelids. In Cephalopods, the egg which contains a large amount of reserves (vitellin) cannot undergo this spiral segmentation.

The larva has a blank shell on its dorsal side. In bivalves and gastropods, the egg grows longer before becoming a veliger larva, which differs from the trochophore by an extra crown of cilia and a prominent fold of the digestive tract. The larva will then undergo a growth of ventral and dorsal side with the appearance of prominences (which become respectively the legs and visceral mass). The digestive tract is folded, which is called endogastric flexion. In Gastropods, the dorsal side of the larva undergoes an extra 180-degree twist to position the mantle cavity over the head. In lamellibranchs, the future mantle forms two symmetrical parts that will evolve into two valves, encompassing the entire body. In cephalopods, the future legs position themselves anteriorly, and bud as tentacles on the dorsal side, and as funnel on the ventral side. As a result of this displacement, the mantle cavity is found in the mouth.

The mesodermal bud does not divide slantwise into segments, which explains the lack of metameres. The cœlom is limited to the (interdependent) pericardial and renal cavity.

In some species the shell does not develop steadily over the years. Growth periods alternate with stagnant periods. The periods of stagnation are mainly related to Climate. Effectively, food availability, particularly calcium, or temperature, directly affects the speed of shell synthesis. Therefore, the growth striae of these species can indicate their age and health.

5.1 PROSOBRANCHS

The prosobranchs found in Sudanian Africa have separate sexes. Bellamia unicolor species are viviparous, and the oviduct is the distal continuation of the uterus in which eggs develop. Embryos are more and more developed as they approach the orifice of the gonoduct. They are

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born with a 2-3mm high shell and begin their independent life. In Lake Chad, sexual maturity is reached at the third month after birth and reproduction is continuous (Leveque, 1973). Melania tuberculala is also viviparous, while Pila are oviparous. In genus Pila, eggs covered with a calcified shell are laid in clusters just on the water surface. Cleopatra are also oviparous whereas the eggs and development are yet unknown. The animal reaches its adult size 3-4 months after birth in Lake Chad.

5.2 PULMONATES

Pulmonates are hermaphrodites. The eggs are laid in gelatinous capsules. In Lymnaea natalensis, the eggs are tubular and transparent in Bulinus and Biomphalaria they are flat, vaguely circular and yellowish. The number of eggs inside the capsule depends both on species and size of individuals belonging in the same species.

5.3 BIVALVES

Unionidae species’ sexes are separated. The fertilized eggs are brooded in the female’s gills, in a pouch-like “marsupium” until the larval stage. The larvae then hatch into gIochidium with two round valves, which is very different from their adult form. These larvae, released by the female, lie on the bottom in wait for a passing fish to stick on then encyst in its epithelium. When they reach maturity several weeks later, they are released and lie on the bottom. The larvae have a well-developed byssus gland which allows them to become attached to the substratum. This gland shrinks gradually and small bivalves then begin their adult lives.

Fryer (1961) studied the larval development of an African Mutelu (Mutelu Bourguignati). In adult females, the eggs are brooded in the gills, where they develop into small larva having a rounded body with hooks and a very long front tentacle. These larvae, released through the exhaling , attach to the fins of Cyprinidae (Barbus) fish. They change afterwards to begin a parasitic development stage. During this phase, the larvae gradually acquire an adult morphology and detach from its (feeder) host when it has reached over 1mm in size. It begins then to live independently.

Mutelidae reproduction appears to occur when the water levels rise. Corbicula brood their many (500 to 1,000) and small (1/6 mm) eggs and embryos in their gills. In Lake Chad,

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bivalves breed once a year, in the cool season. Sphaeridae (Pisidium, Sphaeriurn, Byssanodonta) are hermaphroditic. Their few eggs are brooded in the gills when they have reached a quarter their adult size. They are then transferred through the anal siphon and are almost sexually mature.

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IV. IMPORTANCE OF FRESHWATER MOLLUSCS

1. - IMPORTANCE OF FRESHWATER ECOSYSTEMS

Freshwater ecosystems provide many goods and services such as food intake (protein), water, construction materials, and flood control. The livelihoods of many communities among the poorest in the world depend on resources drawn from freshwater ecosystems.

2. - ECOLOGICAL IMPORTANCE OF FRESHWATER MOLLUSCS

In contrast to marine molluscs, freshwater molluscs are of no primary economic interest. However, they play an important ecological and social role. They are part of the diet of many freshwater fishes and are excellent ecological indicators. The populations of bivalve molluscs play an active role in the sedimentation and purification processes.

Lamellibranchs concentrate many substances such as heavy metals and pesticides.

3. - ROLE OF MOLLUSCS IN HELMINTHIASIS TRANSMISSION

Most freshwater molluscs can transmit one or more species of parasites affecting vertebrates. They are the obligatory hosts for larval stage trematodes to multiply and are eventually responsible for spreading trematodes and cestodes.

In the case of trematods, the eggs hatch in water and spread in an infectious form called “miracidium” that penetrates the molluscs where they multiply in the genital gland and , then giving birth to rediaes. Another free larval form called “cercaria”

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penetrates a final host to become adults as soon as they are released into the aquatic environment.

In Africa, Bulinus and Biomphalaria species are respectively vectors of Schistosoma haematobium (vesical schistosomiasis) and Schistosoma mansoni (intestinal schistosomiasis). Lymnaea transmit Fasciola gigantica (big flukes).

4. SHELLFISH AND MARINE POLLUTION

Shellfish retain toxins when they filter seawater; they therefore constitute a particularly valuable indicator of marine pollution. Three types of contaminants that accumulate in shellfish include chemical residues, microbiological contaminants (due to defects of wastewater treatment devices and agricultural activities) and, for twenty years, toxic substances produced by a certain micro-algal species, which can cause gastro-intestinal or neurological problems, or poisoning if the shellfish are consumed. The secretion of toxic substances was clearly reported for the first time in the 1970s, while pollution significantly spread in the 1990s, before stabilizing in the 2000s.

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V. THREATS TO FRESHWATER SPECIES

Human population growth as well as industrial and agricultural development exerts massive pressure over freshwater systems worldwide. The large quantities of water drawn from rivers, hydropower facilities, construction of dams, pollution, wetlands drainage, river channeling, deforestation causing sedimentation, introduction of invasive species, and overexploitation, all have major impacts on freshwater biodiversity. In addition, climate change, increasing freshwater scarcity and development goals such as improving access to drinking water and hygiene will also have significant impacts in the future.

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VI. MONITORING PROTOCOL FOR SHELLFISH IN THE GAMBIA RIVER BASIN

Monitoring molluscs in The Gambia River Basin will involve the riverbed, floodplains, pools, ponds, etc... This monitoring could be carried out by taking an inventory or census, or through skips and / or dredging.

1.- EQUIPMENT AND METHODS

1.1 EQUIPMENT

1.1.1 SCIENTIFIC TEAM The ideal scientific team will consist of at least one malacologist who will be assisted by a seasoned mollusc taxonomist.

1.1.2 COLLECTION KIT Skips, dredges, and nets must be used to collect species from the malacologic fauna.

1.1.3 SAMPLING PERIODS Sampling will be done when the water level rises/drops in various study sites.

1.1.4 STUDY SITES The study sites are: - Minor riverbed - Floodplains - Ponds, rivers, backwaters, etc. - Non-permanent water holes (ponds disappearing during the dry season and formed by the accumulation of rainwater in a natural depression with a more or less waterproof bottom) - Permanent water holes (supplied by a source and which retain little water or mud still wet until the beginning of the next rainy season)

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1.2 METHODS

1.2.1 METHODS OF HARVEST AND STUDY The inventory to be conducted when the water level rises or drops, will involve upstream and downstream dams.

It is unadvisable to hand-collect African freshwater molluscs, especially pulmonates, as some of them can transmit parasites. Flexible insect pliers are practical for handling the animals without damaging the shell (Douget, 2009).

In the field, a net is well suited to sampling the vegetation. It is however important to carefully inspect the floating vegetal debris, dead leaves and stones since all of these substrates are generally colonized by various species.

In addition, aquatic snails and bivalves can be harvested by means of a landing net or kick net. This is the most suitable and the easiest way to sample shallow wetlands (Douget, 2009).

Sampling in rivers, in particular large rivers, requires techniques that are less easily implemented and more disruptive (using a bucket or dredge for example). For benthic species, using the dredge is usually necessary (Leveque, 1973).

Furthermore, it will be useful to explore different microhabitats (varying the horizontal and vertical strata, etc...), to reach a maximum of species. Taking sediment may, as such, be relevant.

1.2.2 DATA PROCESSING

The data collected will be captured and processed by data processing software (Excel, SPSS, etc.). The information collected in the sampling process will include: - an inventory of fauna followed by a listing of approximate abundance of each species. All the surveyed species are listed on a table and classified according to their collection spot. Both the harvest area and environmental characteristics (depth, type of bottoms, etc.); will be mentioned.

- the study of bio-morphological parameters for bivalves (total length and / or width, and weight, for molluscs in general).

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RECOMMENDATIONS

The preservation of molluscs as resources is essential to ecosystem equilibrium, and requires sound management of the natural environment. Therefore, it is necessary to:

1) Guarantee the survival of breeding shellfish and provide adequate breeding sites so that they can re-colonize the wetlands during the next rise in water level. It is thus crucial to ensure that:  the ponds do not run dry during the dry season, deepen them if need be  the floodplains and wetlands are well protected  the rises of water levels are under control 2) Ensure research studies and environmental preservation as well as a regular monitoring of molluscs. It is also important to identify key species to follow to this end.

BIBLIOGRAPHY

- Brusca (R.C.), Brusca (G.J.), 2003.- Invertebrates (2 éd.). Sinauer Associates. 702 p. - Chu (K. Y.), Arfaa (F. M.), Assoud (J.), 19 66.- The survival of Bulinus truncafus buried in mud under experimental outdoor conditions. Ann. Trop. Med. Parasit., 61 : 6-10. - Daget (J.), 1961.- Note sur les Spathopsis (Mutelidae) de l’Ouest Africain. J. de Conchyl., CI : pp 63-77. - Daget ( J.), 1962.- Note sur les Aspafharia (Mutelidae) de l’Ouest Africain. J. de Conchyl. CI1 : 16-43. - David (M.) & Steven (M.), 1978.- Principles of Paleontology (2 éd.). W.H. Freeman and Co. 4-5. - Douget (G.), 2009.- Mollusques : Gastéropodes aquatiques et bivalves. Invertébrés continentaux des P. de la Loir. Gretia, 371-378. - Fryer (G.), 1961. - Development in a mutelid Lamellibranch. Nafure, 183 : pp 1342-1343. - Gretillat (S.), 1961.- Epidémiologie de la bilharziose vésicale au Sénégal oriental. Observation sur l’écologie de Bulinus guernei et de B. senegalensis. Bull. Org. Mond. Santé, 25, 459-466. - Larivibre (M.), Hocque (T. P.), Ranque (P.), 1962. - Giude de la résistance à l’andydrobiose des Gastropodes d’eau douce Bulinus guernei Dautzenberg et Biomphalaria pfeiferi gaudi Ranson C. R. Séances Soc. Biologie, CLVI, 4 : 725-726. - Lecointre, G. & Le Guyader G. 2006.- Classification phylogénétique du vivant, 3e édition, Belin, Paris. - Lévêque (C.), 1968.- Biologie de Bulinus forskali (Mollusque, Gastbropode) de la region de Fort-Lamy (Tchad). Cah. O.R.S.T.O.M., sir. Hydrobiol., II, 2 : 79-90. - Lévêque (C.), 1972. - Mollusques benthiques du lac Tchad : Ecologie, Etude des peuplements et estimations des biomasses. Cah. O.R.S.T.O.M., Sér. Hydrobiol., VI, 1 : 3-45. - Lévêque (C.), 1973. - Dynamique des peuplements, biologie, et estimation de la production des mollusques benthiques du lac Tchad. Cah. O.R.S.T.O.M., S ér. Hydrobiol.,VII, 2 : 117-147. - Lévêque (C.), 1975. - Mollusques des herbiers à Ceratophyllum du lac Tchad: biomasses et variations saisonnières de la densité. Cah. O.R.S.T.O.M., sér. Hydrobiol., IX, 1 : 25-31. - Romaric (F.), 2006. « Malacologie », Dico de Bio, 2e éd. De Boeck Université. - Ruppert (E.E.), Fox (R.S.), & Barnes (R.D.), 2004.- Invertebrate Zoology (7 éd.). Brooks / Cole. 367-403. - Skinner (J.), Beaumond (N.) & Pirot (J. Y.), 1994.- Manuel de formation à la gestion des zones humides tropicales. UICN, 272 p. - UICN, 2008. Biodiversité des eaux douces – une ressource cachée et menacée. Commission de la sauvegarde des espèces.

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ANNEX

Annex 1: List of molluscs found in The Gambia River Bassin

Genus Species Author-Year Afrogyrus coretus (Blainville, 1826) Aspatharia dahomeyensis (Lea, 1859) Aspatharia mabillei (Jousseaume, 1886) Aspatharia tawai (Rang, 1835) Aspatharia Chaiziana (Rang, 1835) Bellamya Unicolor (Olivier, 1804) Biomphalaria Pfeifferi (Krauss, 1848) Bulinus truncates (Audouin, 1827) Bulinus senegalensis Müller, 1781 Bulinus forskalii (Ehrenberg, 1831) Bulinus globosus (Morelet, 1866, 1868) Bulinus umbilicatus Mandahl-Barth, 1973 Bulinus jousseaumei (Dautzenberg, 1890) Caelatura aegyptiaca (Cailliaud, 1827) Chambardia wahlbergi tabula (Sowerby, 1867) Chambardia rubens rubens (Lamarck, 1819) Cleopatra bulimoides (Olivier, 1804) Corbicula fluminalis consobrina (Müller, 1774) Cyrenoida dupontia Joannis, 1835 Etheria elliptica Lamarck, 1807 Eupera ferruginea (Krauss, 1848) Gyraulus costulatus (Krauss, 1848) Lanistes varicus (Müller, 1774) Lymnaea natalensis Krauss, 1848 Melampus liberianus H. & A. Adams, 1854 Melanoides tuberculata (Mûller, 1774) Mutela dubia dubia (Gmelin, 1791) Mutela rostrata (Rang, 1835) Mytilopsis africanus (Van Beneden, 1835) Neritina rubricata Morelet, 1858 Neritina adansoniana (Récluz, 1841) Neritina glabrata Sowerby, 1849 (Müller, 1774) (Gmelin, 1791) Pleiodon ovatus (Swainson, 1823) Segmentorbis kanisaensis (Preston, 1914) Sphaerium hartmanni courteti Germain, 1904 Tympanotonus fuscatus (Linnaeus, 1758)

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