Brackish water snails are suspected to be an intermediate host of trematode diseases in vertebrates. The aim of this

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1 JITMM Proceedings J I T M M Proceedings 3 (5) -5 CERCARIAL INFECTIONS OF BRACKISH WATER SNAILS ON THE EAST COAST OF SOUTHERN THAILAND Supatta Sritongtae, Suluck Namchote, Duangduen Krailas, Dusit Boonmekam, Tunyarut Koonchornboon Parasitology and Medical Malacology Research Unit, Department of Biology, Faculty of Science, Silpakorn University, Nakhon Pathom, Thailand Department of Anatomy, Pramongkhutklao College of Medicine, Bangkok, Thailand ABSTRACT Brackish water snails are suspected to be an intermediate host of trematode diseases in vertebrates. The aim of this study is cercarial investigation of brackish water snails on the east coast of Southern Thailand. Snails were collected from forty-one localities of mangrove forest and estuaries in six provinces (Phetchaburi, Phachuap Khiri Khan, Chumphon, Surat Thani, Nakhon Si Thammarat, Songkhla) between June 3 and March 4. Five collectors picked the snails by hand and scoop for minutes at each station. A total of 8,79 brackish water snails were classified into ten families. They were Neritidae, Ellobiidae, Haminoeidae, Muricidae, Nassariidae, Littorinidae, Stenothyridae, Thiaridae, Potamididae and Assimineidae. Seven species found with trematode infections, they were Cerithidea cingulata, Cerithidea djadjariensis, Cerithidea alata, Cerithidea quadrata, Clithon pequensis, Sermyla riqueti and Assiminea brevicula. The infection rates were.9% (7/8,79),.5% (4/8,79),.% (/8,79),.% (/8,79),.5% (4/8,79),.7% (63/8,79) and.7% (7/8,79), respectively. The cercariae were classified into nine species. They were Cloacitrema philippinum, Parorchis acanthus, Haplorchis taichui, Metorchis intermedius, Stictodora tridactyla, Ascorhytis charadriformis, lava of Mesostephanus appendiculatoides, Hypoderaeum conoideum and Himasthla interrupta. Keyword: brackish water, snail, trematode infections, the South of Thailand INTRODUCTION Recently, the rapid economic expansion in Thailand has caused the loss of coastal habitat, and prompted the government to introduce a conservation and restoration policy for mangrove habitats. The estuary and mangrove areas in the South were a major source of brackish water fishing and natural habitat of many animals including brackish water snails. About 4 species of brackish Correspondence: Suluck Namchote, Department of Biology, Faculty of Science, Silpakorn University, Nakhon Pathom 73, Thailand. Tel/Fax: / s: Namchote@hotmail.com water snail were reported in the Gulf of Siam, Thailand (Sri-aroon et al, 4). It is well known that snails could be the first intermediate host of human and animal trematodes. In Thailand, snails in Family Potamididae (Cerithidea cingulata, C. djadijarensis and C. charbonnieri) could be the intermediate host of 3 groups of cercariae: the first group have cystogenous glands but no eye spots or collar spines; the second group with eye spots, 3-4 penetration glands and finfold tail; while the third group has not identified yet (Sri-aroon et al, 5). So, the objectives of this study were to investigate:.) The infection rate of cercariae in brackish water snails.) The types of cercariae found in snails. Information from this study could be used in controlling the infection rate of trematodes in animals and humans in Thailand. Vol 4 5

2 MATERIALS AND METHODS Collection of brackish water snails Brackish water snails were collected from forty one localities between June 3 and March 4. These localities were in six provinces: Phetchaburi, Phachuap Khiri Khan, Chumphon, Surat Thani, Nakhon Si Thammarat and Songkhla (Figure ). Two types of localities were investigated, mangrove forest and river estuaries. The counts per unit of time method was used for snail sampling. Five collectors picked the snails by hand and scoop for minutes at each station. The brackish water snails were identified by shell morphology (Brandt, 974; Upathum et al, 983), before all being examined for cercarial infections. Examination for trematode infections Cercariae were studied by using shedding and crushing methods. The cercariae were placed in dechlorinated water and examined under a stereo-microscope. The swimming behavior was also observed (Krilas et al, 3). After crushing, the flesh of each snail was examined under a microscope for sporocysts and rediae. Study of cercarial morphology Cercariae were stained with.5% neutral red and identified under light microscope by their morphology. They were drawn using camera lucida. Scanning electron microscopes were used for fine images. The cercariae were fixed in.5% glutaraldehyde phosphate buffer at 4 C for at least hours and post-fixed in % osmium tetroxide at 4 C for hour, dehydrated through a graded series of acetone, before they were air dried. The specimens were adhered to a carbon stub, coated with gold-palladium in an ion-sputtering apparatus (Polaron CPD 75, UK), and then examined under a Camscan MX scanning electron microscope (UK). RESULTS Fig. - Map of Southern Thailand showing the 6 surveyed provinces:. Phetchaburi (-3);. Phachuap Khiri Khan (4-); 3. Chumphon (3-8); 4. Surat Thani (9-34); 5. Nakhon Si Thammarat (35-4); 6. Songkhla (4). Snail samples A total of 8,79 brackish water snails were collected from six provinces (Table ). Snail samples were classified into ten families. They were Neritidae, Ellobiidae, Haminoeidae, Muricidae, Nassariidae, Littorinidae, Stenothyridae, Thiaridae, Potamididae and Assimineidae. These were subclassified into genera and 33 species. They were Assiminea brevicula, Cassidula aurisfelis, Cassidula mustelina, Cassidula multiplicata, Ellobium aurisjudae, Laemodonta punctigera, Laemodonta siamensis, Melampus siamensis, Littorinopsis intermedia, Littorinopsis scabra, Littorinopsis melanostoma, Chicoreus capucinus, Alectrion taenia, Nassarius sp., Nassarius stolatus, Clithon peguensis, Dostia violacea, Neritodryas cornea, Neritodryas dubia, Cerithidea alata, Cerithidea charbonieri, Cerithidea cingulata, Cerithidea djadjariensis, Cerithidea quadrata, Vol 4 5

3 Table Brackish water snails in the Gulf of Southern Thailand. Province* / Number of snails Family Genus / Species Total Assimineidae. Assiminea brevicula Ellobiidae. Cassidula aurisfelis 3. Cassidula mustelina 4. Cassidula multiplicata 5. Ellobium aurisjudae 6. Laemodonta punctigera 7. Laemodonta siamensis 8. Melampus siamensis Haminoeidae 9. Haminoea sp. 5 5 Littorinidae. Littorinopsis intermedia. Littorinopsis scabra. Littorinopsis melanostoma Muricidae 3. Chicoreus capucinus 4. Alectrion taenia Nassariidae 5. Nassarius sp. 6. Nassarius stolatus Neritidae 7. Clithon peguensis 8. Dostia violacea 9. Neritodryas cornea. Neritodryas dubia Potamididae. Cerithidea alata. Cerithidea charbonieri 3. Cerithidea cingulata 4. Cerithidea djadjariensis 5. Cerithidea quadrata 6. Cerithidea obtusa 7. Telescopium telescopium 8. Faunus ater , Stenothyridae 9. Stenothyra sp Thiaridae 3. Melanoides tuberculata 3. Sermyla riqueti 3. Tarebia granifera 33. Pseudoplotia (Thiara) scabra ,633 4 Total 3,74, ,68 8,79 * Province:. Phetchaburi,. Phachuap Khiri Khan, 3. Chumphon, 4. Surat Thani, 5. Nakhon Si Thammarat, 6. Songkhla Vol 4 5 3

4 Cerithidea obtusa, Telescopium telescopium, Faunus ater, Stenothyra sp., Melanoides tuberculata, Sermyla riqueti, Tarebia granifera, Pseudoplotia (Thiara) scabra and Haminoea sp. Cercarial infections in brackish water snails Seven species of snails were found with cercarial infections. They were Sermyla riqueti, Cerithidea cingulata, Assiminea brevicula, Cerithidea djadjariensis, Clithon pequensis, Cerithidea quadrata and Cerithidea alata (Figure ). The infection rates were.7% (63/8,79),.9% (7/8,79),.7% (7/8,79),.5% (4/8,79),.5% (4/8,79),.% (/8,79) and.% (/8,79), respectively. The cercariae were categorized into five types and nine species. The first type was Parapleurophocercous cercariae; they consisted of Haplorchis taichui, Metorchis intermedius and Stictodora tridactyla. The second type was Xiphidiocercariae; it was Ascorhytis charadriformis. The third type was Furcocercous cercariae; namely the lava of Mesostephanus appendiculatoides. The fourth type was Echinostome cercariae; they consisted of Hypoderaeum conoideum and Himasthla interrupta. The fifth type was Megalurous cercariae; they consisted of Cloacitrema philippinum and Paraorchis acanthus (Table ). Morphology of cercariae Characteristics of cercariae were classified from living cercariae, fixed cercariae under light microscope, cercarial images from scanning electron microscope, and the size of cercariae. Type. Parapleurophocercous cercariae. Haplorchis taichui (Nishigori, 94) Witenberg, 93 The body was oval in shape. Skin was covered with minute spines and sensory hairs. An oral sucker was situated in the head region. There were spines around the mouth aperture. One pair of eye spots and a pharynx were present. Seven pairs of penetration glands extended from the pharynx to the end of the body. There were two longitudinal rows of genital primodia. The excretory bladder Fig. - Shell of infected brackish water snails: a. Assiminea brevicula, b. Clithon pequensis, c. Sermyla riqueti, d. Cerithidea cingulata, e. Cerithidea alata, f. Cerithidea quadrata and g. Cerithidea djadjariensis 4 Vol 4 5

5 Table Infection rate of cercariae from brackish water snails (8,79 snails) in the Gulf of Thailand. Cercariae species No. infected snails Infection rate (%) Species of snails Type. Parapleurophocercous Cercariae. Haplorchis taichui. Metorchis intermedius 3. Stictodora tridactyla 63/8,79 /8,79 /8, Sermyla riqueti Assiminea brevicula Cerithidea cingulata Type. Xiphidiocercarriae 4. Ascorhytis charadriformis / 8,79.3 Assiminea brevicula, Clithon peguensis Type 3. Furcocercous cercariae 5. Lava of Mesostephanus appendiculatoidas Type 4. Echinostome cercariae 6. Hypoderaeum conoideum 7. Himasthla interrupta Type 5. Megalurous cercariae 8. Parorchis acanthus 9. Cloacitrema philippinum / 8,79. Cerithidea cingulata, Cerithidea djadjariensis /8,79 3/8,79 9/8,79 5/8, Cerithidea djadjariensis Cerithidea cingulata Cerithidea cingulata, Cerithidea djadjariensis Cerithidea alata, Cerithidea cingulata, Cerithidea quadrata Total 97/8,79. 7 species had a round shape and was composed of fine pigments. A long tail was attached to the dorsal end of the body, with lateral finfolds and a dorso-ventral finfold for the greater distal portion. Cercariae were produced within the rediae (Figure 3). The following are size ranges and average sizes (in micrometers, calculated from cercariae): Eye spot: Oral sucker: 58-4 µm (av. 8 µm) x 3-53 µm (av. 9 m) 8-3 µm (av. 5 µm) x µm (av. 379 µm) 3-8 µm (av. 8 µm) x 8- µm (av. 8 µm) 33-4 µm (av. 36 µm) x µm (av. 44 µm) Ventral sucker: -3 µm (av. µm) x 8-3 µm (av. µm) 3-8 µm (av. 6 µm) x 3- µm (av. 6 µm) Excretory bladder: µm (av. 7 µm) x µm (av. 63 µm) Lateral finfold: 8-8 µm (av. 4 µm) x 63-4 µm (av. 6 µm) Dorso-ventral finfold: 8-8 µm (av. 4 µm) x µm (av. 53 µm). Metorchis intermedius Heinemann, 937 The body was oval shaped and yellowish brown in color. There were 4 rows of oral spines and a long prepharynx. Esophagus and ceca were not found. Eye spots were apparently without a lens. Vol 4 5 5

6 4 penetration glands formed compact median groups of 3, 4, 4 and 3. The ventral sucker was a prevesicular median mass of cells. The excretory vesicle was round and lined with epithelia. Tail tubule median opened at a distance from the base of the tail. The dorsal finfold began at the posterior end of the basal swelling and passed over to the ventral finfold to reach the middle of the tail. Cercariae were produced within the rediae (Figure 4). The following are size ranges and average sizes (in micrometers, calculated from cercariae): Fig. 3- Haplochis taichui cercaria: a. drawing image, b-c. light micrograph, d-g. SEM micrograph of cercaria. (os = oral sucker, es = eye spot, pg = penetration gland, eb = excretory bladder, sp = spine, ta = tail, lf = lateral finfold, df = dorso- ventral finfold, c = cercaria, re = redia)(scale bar = 5µm) 6 Vol 4 5

7 Fig. 4- Metorchis intermedius cercaria: a. drawing image, b-c. light micrograph, d-g. SEM micrograph of cercaria. (os = oral sucker, es = eye spot, pg = penetration gland, eb = excretory bladder, ta = tail, lf = lateral finfold, df = dorso-ventral finfold, c = cercaria)(scale bar = 5 µm) Eye spot: Oral sucker: Ventral sucker: µm (av. 4 µm) x 75-3 µm (av. 88 µm) 5-35 µm (av. 3 µm) x µm (av. 333 µm) 3-8 µm (av. 8 m) x 8- µm (av. 8 m) 33-4 µm (av. 36 µm) x µm (av. 44 µm) -3 µm (av. µm) x 8-3 µm (av. µm) 3-8 µm (av. 6 µm) x 3- µm (av. 6 µm) Excretory bladder: µm (av. 7 µm) x µm (av. 63 µm) Lateral finfold: 3 µm (av. 3 µm) x 33 µm (av. 33 µm) Dorso-ventral finfold: 33 µm (av. 33 µm) x 88 µm (av. 88 µm) 3. Stictodora tridactyla Martin et Kuntz, 955 The body was oval in shape and yellowish brown in color. There were 3 row of oral spines (5:8:8) and 7 pairs of penetration glands were presented. The ventral sucker was small. Eye Vol 4 5 7

8 spots were present, with a small globular pharynx between the eye spots. The excretory bladder in the flattened V-shape was situated at the end of the body. The tail was longer than the body with a bilaterial finfold and a dorso-ventral finfold. Both the dorsal and ventral finfolds arose at a short distance from the anterior and the posterior end of the lateral finfold. Cercariae were produced within the rediae (Figure 5). The following are size ranges and average sizes (in micrometers, calculated from cercariae): Fig. 5- Stictodora tridactyla cercaria: a. drawing image, b-c. light micrograph, d-g. SEM micrograph of cercaria. (os = oral sucker, es = eye spot, pg = penetration gland, eb = excretory bladder, b = body, ta = tail, lf = lateral finfold, df = dorso- ventral finfold, c = cercaria, re = redia)(scale bar = 5 µm) 8 Vol 4 5

9 78-5 µm (av. 94 µm) x 8-83 µm (av. 43 µm) 5-38 µm (av. 3 µm) x µm (av. 43 µm) Eye spot: -3 µm (av. µm) x 5- µm (av. 9 µm) Oral sucker: 8-38 µm (av. 3 µm) x 8-38 µm (av. 33 µm) Ventral sucker: 3-5 µm (av. 3 µm) x 5 µm (av. 5 µm) -3 µm (av. µm) x 8-3 µm (av. µm) Excretory bladder: 5-5 µm (av. 4 µm) x -5 µm (av. 9 µm) Lateral finfold: 5-3 µm (av. 8 µm) x µm(av. 6 µm) Dorso-ventral finfold: 3-5 µm (av. 6 µm) x 95-3 µm (av. 87 µm) Type. Xiphidiocercariae 4. Ascorhytis charadriformis (Young, 949) Ching, 965 The body was oval in shape and white in color. The stylet was long, with a long sharp point and 4 pairs of penetration glands. The ventral sucker was bigger than the oral sucker. The excretory bladder was bicornuate. The tail was round. The excretory duct opened at the end of tail. Cercariae were produced within the sporocyst (Figure 6). The following are size ranges and average sizes (in micrometers, calculated from cercariae): -38 µm (av. 3 µm) x 4-48 µm (av. 46 µm) 8- µm (av. 9 µm) x - 5 µm (av. 6 µm) Oral sucker: 8-3 µm (av. 9 µm) x 3-8 µm (av. 6 µm) Ventral sucker: -3 µm (av. µm) x 3 µm (av. 3 µm) Excretory bladder: 8- µm (av. 9 µm) x 3 µm (av. 3 µm) Stylet:.5 µm (av..5 µm) x µm (av. µm) Fig. 6- Ascorhytis charadriformis cercaria: a. drawing image, b-c. light micrograph, d-g. SEM micrograph of cercaria. (s = stylet, os = oral sucker, vs = ventral sucker, pg = penetration gland, eb = excretory bladder, b = body, ta = tail, sp = spine, c = cercaria, spo = sporocyst, sh = sensory hair) (scale bar = µm) Type 3. Furcocercous cercariae 5. Lava of Mesostephanus appendiculatoides (Price, 934) Lutz, 935 The body was oval in shape. The surface of the body and the oral sucker were found with spines. The pharynx was small and round. There was both a prepharynx and esophagus, each was almost as long as the pharynx. The large intestine terminated near a small excretory bladder. The ventral sucker was small. The tail was forked and longer than the body, and the tail stem was longer Vol 4 5 9

10 than the furca. The tail tubule opened at the tip of each tail furca. Cercariae were produced within the sporocyst (Figure 7). The following are size ranges and average sizes (in micrometers, calculated from cercariae): µm (av. 48 µm) x 3-55 µm (av. 37 µm) 5-73 µm (av. 66 µm) x µm (av. 98 µm) Tail furcal: Oral sucker: Ventral sucker: Excretory bladder: 3-5 µm (av. µm) x 3-63 µm (av. 5 µm) 38-5 µm (av. 45 µm) x 38-5 µm (av. 45 µm) 3-5 µm (av. 3 µm) x 3- µm (av. 5 µm) -8 µm (av. 3 µm) x -3 µm (av. µm) 8-5 µm (av. 3 µm) x -33 µm (av. 5 µm) Fig. 7- Lava of Mesostephanus appendiculatoides cercaria: a. drawing image, b-c. light micrograph, d-g. SEM micrograph of cercaria. (os = oral sucker, p = pharynx, in = intestine, eb = excretory bladder, et = excretory tube, ta = tail, c = cercaria, re = redia, ff = furcal finfold, fu = furcal tail, b = body, sp = spine, sh = sensory hair, spa = sensory papillae)(scale bar = µm) Vol 4 5

11 Type 4. Echinostome cercariae 6. Hypoderaeum conoideum (Bloch, 98) Dietz, 99 The body was Round in shape and colorless. There was no eye spot. There were collar spines with two alternating rows, and the prepharynx was long. The pharynx was round. The esophagus was long, and bifurcate ceca terminated at the posterior end of the body. The excretory vesicle was a simple sac. There was a Y-shaped excretory tube at the tail, the tube opened at the lateral side of the tail around one-third of the tail length from its base. Cercariae were produced within the rediae (Figure 8). The following are size ranges and average sizes (in micrometers, calculated from cercariae): Oral sucker: Ventral sucker: Excretory bladder: µm (av. 5 µm) x µm (av. 4 µm) 3-38 µm (av. 33 µm) x 38-5 µm (av. 4 µm) µm (av. 4 µm) x µm (av. 4 µm) 55-7 µm (av. 6 µm) x µm (av. 54 µm) - µm (av. 4 µm) x 8-5 µm (av. 3 µm) 5-5 µm (av. 3 µm) x 8-5 µm (av. 3 µm) Fig. 8- Hypoderaeum conoideam cercaria: a. drawing image, b-c. light micrograph, d-g. SEM micrograph of cercaria. (os = oral sucker, p = pharynx, in = intestine, vs = ventral sucker, eb = excretory bladder, et = excretory tube, ta = tail, c = cercaria, re = redia, ex = excretory pore, sc = collar spines, spa = sensory papillae)(scale bar = 5 µm) Vol 4 5

12 7. Himasthla interrupta Loos-Frank, 967 The body was cylindrically shaped and colorless, with the tail extending beyond the head to rest directly on the substratum. It was eyeless, but attracted to light. There was a pair of head papillae, each bearing hairs, anterolateral to the oral sucker. There was one row of small collar spines. The penetration gland was on the ventral side of fore body between the esophagus and main excretory vessel. There was a T-shaped excretory tube at the tail, the tube opened lateral to the tail around one-fourth of the tail length from its base. Cercariae were produced within the rediae (Figure 9). The following are size ranges and average sizes (in micrometers, calculated from cercariae): Oral sucker: Ventral sucker: Excretory bladder: 5-63 µm (av. 5 µm) x µm (av. 7 µm) 8-4 µm (av. 34 µm) x µm (av. 4 µm) µm (av. 44 µm) x µm (av. 44 µm) 4-73 µm (av. 6 µm) x µm (av. 6 µm) 3-8 µm (av. 4 m) x -3 µm (av. 4 m) 8-55 µm (av. 38 µm) x 8-55 µm (av. 33 m) Type 5. Megalurous cercariae 8. Cloacitrema philippinum Velasquez, 969 The body was elongated and muscular. There were long prepharynx and pharynx. There were long ceca. The oral suckers had opening ducts. The cystogenous cells were found all over the body. There was thin walled excretory vesicle, and the ventral sucker was bigger than the oral sucker. A long tail extended from the posterior end of the body, and clear vacuoles were distributed along the tail. There was an adhesive organ at the tip of the tail, and cercariae were produced within the rediae (Figure ). The following are size ranges and average sizes (in micrometers, calculated from cercariae): Fig. 9- Himasthla interrupta cercaria: a. drawing image, b-c. light micrograph, d-g. SEM micrograph of cercaria. (os = oral sucker, spa = sensory papillae, cs = collar spines, p = pharynx, ep = esophagus, in = intestine, vs = ventral sucker, eb = excretory bladder, et = excretory tube, b = body, ta = tail, c = cercaria, re = redia)(scale bar = 5 µm) Oral sucker: Ventral sucker: Excretory bladder: -34 µm (av. 49 µm) x 4-55 µm (av. 494 µm) 5-8 µm (av. 7 µm) x 3-4 µm (av. 349 µm) 8-9 µm (av. 89 µm) x 8-9 µm (av. 85 µm) 3-5 µm (av. 36 µm) x -4 µm (av. 4 µm) 3-5 µm (av. 34 µm) x 4-5 µm (av. 46 µm) 5-5 µm (av. 3 µm) x 8-5 µm (av. 3 µm) Vol 4 5

13 Fig. - Cloacitrema philippinum cercaria: a. drawing image, b-c. light micrograph, d-g. SEM micrograph of cercaria. (os = oral sucker, p = pharynx, in = intestine, vs = ventral sucker, eb = excretory bladder, et = excretory tube, ta = tail, ad = adhesive gland cell, spa = sensory papillae, c = cercaria, re = redia)(scale bar = 5 µm) 9. Paraorchis acanthus (Nicoll, 96) Nicoll, 97 The body was cylindrical in shape and colorless. The cuticle was armed with transverse rows of flat, triangular alternate spines. The collar spines were single row. The cuticle in front of collar bears 3 transverse rows of sensory papillae. The excretory vesicle was pyriform. The tail was with a smooth cuticle; its tip always introverted, forming a sucker-like structure probably secreted an adhesive substance. The tail tubule bifurcated short of length and opened at the lateral of the tail (Figure ). The following are size ranges and average sizes (in micrometers, calculated from cercariae): Oral sucker: Ventral sucker: Excretory bladder: 7-3 µm (av. 87 µm) x 8-9 µm (av. 863 µm) 7-7 µm (av. 7 m) x 39-4 µm (av. 43 µm) 6-6 µm (av. 6 µm) x 5-6 µm (av. 57 µm) 7-8 µm (av. 73 µm) x 6-7 µm (av. 67 µm) 3-5 µm (av. 37 µm) x 3-4 µm (av. 37 µm) 7-3 µm (av. µm) x 4-6 µm (av. 5 m) Vol 4 5 3

14 Fig. - Paraorchis acanthus cercaria: a. drawing image, b-c. light micrograph, d-g. SEM micrograph of cercaria. (os = oral sucker, p = pharynx, ep = esophagus, in = intestine, vs = ventral sucker, eb = excretory bladder, et = excretory tube, ta = tail, ad = adhesive gland cell, spa = sensory papillae, c = cercaria, re = redia)(scale bar = 5 µm) DISCUSSION The species diversity of snails was studied along the east coast of Southern Thailand. The snails were classified into ten families by referring to the Non-Marine Aquatic Mollusca of Thailand (Brandt, 974). There were three families that differed from the report of species diversity of brackish water snails on the eastern coast of Thailand, nine families of snails were reported (Sriaroon et al, 4). Two familes, Haminoeidae and Nassariidae, were not reported, while family Iravadiidae was not found in this study. Thirtythree species were collected, including eight species of snails which were not reported in the previous study in the same collection area. They were Laemodonta punctigera, Laemodonta siamensis, Haminoea sp., Nassarius sp., Nassarius stolatus, Clithon peguensis, Neritodryas dubia and Cerithidea charbonieri. However, Brandt 4 Vol 4 5

15 (974) reported that 43 species of brackish water molluscs inhabit in Thailand. Two species of Cerithidea charbonnieri and Morrisonietta bandonensis were reported only in Surat Thani province. Seven species of brackish water snails were found with cercarial infections, making them the intermediate host of trematodes. Cerithidea cingulate, C. djadjariensis and C. quadrata were infected with trematode larvae as in the survey in the Surat Thani province. High infection rates of snails were recorded in C. cingulata, even higher than the report after the Indian Ocean tsunami occurred in December 4. (Sriaroon et al, 5; Sriaroon et al, ). The cercariae were identified into nine species according to morphology and organ characteristics (Schell, 97; Yamaguti, 975; Ito, 98). Cerithidea cingulata were infected by five species of the trematodes; they were Stictodora tridactyla, Mesostephanus appendiculatoidas, Himasthla interrupta, Parorchis acanthus and Cloacitrema philippinum. This snail was susceptible to a wide range of trematodes. Moreover, C. cingulata in the most widespread mollusc in Thailand. Sermyla riqueti had the highest infection rate which was.7% (63/8,79). The species of cercaria Haplorchis taichui caused a major public health problem in SEA (Chai et al, 5). In a previous study of cercarial infections in Thiaridae snails from the south of Thailand, H. taichui were found in S. riqueti (Krailas et al, ). The larvae of Mesostephanus appendiculatoides, blood fluke of birds, were observed in C. cingulata and C. djadjariensis. The present study has applications for reseach of medical malacology in Thailand. ACKNOWLEDGEMENTS This work was supported by Faculty of Science, Silpakorn University, Thailand. REFERENCES Brandt AM. The Non-Marine Aquatic Mollusca of Thailand. Arch Molluskenkund 974;5:- 43. Chai JY, Murrell KD, Lymbery AJ. Fish-borne parasitic zoonoses: status and issues. Int J Parasitol 5;35: Ito J. Studies on cercariae in Janpan. Shizuoka University. Oya, Surugaku, Shizuoka 98; Krailas D, Dechruksa W, Ukong S, Janecharut T. Cercarial Infection in Paludomus petrosus freshwater snail in Pa La-U waterfall. Southeast Asian J Trop Med Public Health 3;34: Krailas D, Namchote S, Rattanathai P. Human intestinal flukes Haplorchris taichui and Haplorchris pumilio in their intermediate hosts, freshwater snails of the families Thiaridae and Pachyilidae, in southern Thailand. Zoosyst Evol ;87(): Schell SC. How to know the Trematode. W. C. Brown Publishers, Iowa 97. Sri-aroon P, Lohachit C, Harada M. Survey of brackish water snails in eastern Thailand. Southeast Asian J Trop Med Public Health 4;35:5-55. Sri-aroon P, Lohachit C, Harada M. Brackish water Mollusks of Surat Thani Province, Southern Thailand. Southeast Asian J Trop Med Public Health 5;36:8-88. Sri-aroon P, Chusongsang P, Chusongsang Y, Surinthwong P, Butraporn P, Lohachit C. Snails and trematode infection after Indian Ocean tsunami in Phang-Nga province, Southern Thailand. Southeast Asian J Trop Med Public Health ;4:48-6. Upatham ES, Sornmani S, Kitikoon V, Lohachit C, Burch JB. Identification key for the freshwater and brackish water snails of Thailand. Malacol Rev 983;6:7-3. Yamaguti S. A synoptical review of life histories of digenetic Trematode of Vertebrates. Kyoto: Japan 975:-59. Vol 4 5 5