Surface ultrastructure of Pygidiopsis summa (Digenea: Heterophyidae) adult flukes

A scanning electron microscopic study was performed on the surface ultrastructure of Pygidiopsis summa (Digenea: Heterophyidae) adults. Metacercariae were collected from gills and muscles of mullets (Mugil cephalus) caught in a known endemic area, and adult flukes were harvested from dogs after 8 weeks of experimental infection. The worm was calabash form with its posterior part broader than the anterior part. Tegumental spines were densely distributed over the body surface, except on the suckers and genital apparatus, and around the excretory pore. Well differentiated spines were observed on the anterior half of the body, with 14-16 tips ventrally, and 19-20 tips dorsally. On the oral sucker, three pairs of type I sensory papillae (uni-ciliated knob-like swellings) and one pair of type II sensory papillae (aciliated round-swellings) were observed on the anterior and posterior parts of the lip, respectively. On the lip of the ventral sucker, one pair of type II sensory papillae was distributed only on its posterior part. Sperms were seen emerging from or entering into the genital apparatus. The results showed that the surface ultrastructure of P. summa was unique among the heterophyid trematodes, especially in digitation of tegumental spines and in distribution of sensory papillae on oral and ventral suckers.     

Localisation of parasite antigens and inflammatory responses in experimental opisthorchiasis

The time course localisation of parasite antigens and related host pathology were studied in hamsters infected with 100 metacercariae of Opisthorchis viverrini for up to 6 months. Parasite antigens, as detected by immunofluorescence and/or immunoperoxidase-staining, were first observed in the flukes and the biliary epithelium of the intrahepatic and extrahepatic bile ducts as early as day 3 p.i. Antigens increased as the parasite matured, both in tissues in direct contact with the flukes and those surrounding the infection. Opisthorchis antigens were also observed in the first order bile ducts (small bile ducts) of the liver, which are not normally inhabited by flukes. In addition, they were found in damaged liver cells, Kupffer cells, macrophages, and within epithelioid and giant cells in the egg granuloma. The presence of the antigens was associated with heavy inflammatory cell infiltration, particularly with mononuclear cells. The results strongly support the role of fluke-associated antigens and local parasite-specific immune responses in the pathogenesis of opisthorchiasis.     

Periodic shedding and replacement of venomous caudal spines,with special reference to South American freshwater stingrays,Potamotrygon spp.

Synopsis The number of venomous caudal spines and their length and position relative to one another were determined in seven species of South American freshwater rays (Potamotrygonidae) and eight marine or euryhaline species of four families from the Caribbean Coast of South and Central America. Most species have two visible spines at certain stages in the shedding-replacement cycle and only one visible spine at other stages (following shedding). If we include the embryological beginnings of the spines before they erupt and become visible, the spine counts of most rays are actually 2 rather than 1 or 2. Since most species apparently follow this pattern, spine counts are of little use in distinguishing between species except in the relatively few that may have only one, or no spines. Eight captive Potamotrygon specimens maintained in simulated tropical temperature conditions over 12 months showed periodic shedding and replacement of spines. The molts were biannual for a given ray but annual for a given spine. They alternated between two spine loci and their cycles were approximately six months out of phase with each other. Recent studies on Dasyatis sabina by others report only one molt per year, with replacement spines forming always posterior to the primary spine rather than alternating between posterior and anterior. Supernumerary spines (counts of more than two, up to five) are also discussed, as are counts of one and zero.     

Fasciola hepatica: Surface tegumental responses to in vitro and in vivo treatment with the experimental fasciolicide OZ78

The tegumental alterations in adult Fasciola hepatica induced by the experimental fasciolide OZ78 were investigated utilizing scanning electron microscopy (SEM). Twelve weeks post-infection with F. hepatica, rats were treated with a single 100mg/kg oral dose of OZ78 and flukes were recovered from the bile ducts after 24-72 h. In vitro F. hepatica were incubated with OZ78 for 48 h at a concentration of 10 microg/ml in the absence or presence of haemin. Twenty-four and 48 h post-treatment of rats disruption of the tegument of F. hepatica as blebbing, swelling and furrowing was evident. The recovery of flukes 72 h post-treatment was low. Flukes examined at this time point showed an increasing severity of tegumental damage as sloughing and absence of spines, in particular in the tail region. SEM analysis of F. hepatica incubated in the presence of OZ78 without haemin showed only minor and localized damage of the tegument. In the presence of haemin extensive tegumental damage, including sloughing or blebbing, in particular in the anterior part, was observed. In conclusion, our experiments confirm the interesting fasciocidal properties of OZ78. The tegument of adult F. hepatica might play a role in the action of this drug.     

剪形臂尾轮虫形态的时空变化及其与生态因子间的关系

对芜湖市镜湖和汀棠湖中剪形臂尾轮虫(Brachionus forficula)的发生及其形态特征进行了一年的观察,并分析了其与环境因子间的关系。结果表明,镜湖中,剪形臂尾轮虫出现于7月至10月,且仅存在短后棘刺型个体;2样点内,除了前外棘刺长以外,轮虫的其他各形态参数均随季节显著变化,形态参数的样点间差异也因季节的不同而异;轮虫的各形态参数均随pH的升高而延长,随过滤水体中叶绿素a含量和水体中总叶绿素a含量的升高而缩短;体长和体宽均随晶囊轮虫密度的升高而增大。汀棠湖中,短后棘刺型个体出现于6月至10月,而长后棘刺型个体仅出现于6月至8月;2种形态型个体同时存在时,长后棘刺型个体在种群中所占比例始终高于短后棘刺型个体,并与水温、水体中总叶绿素a含量以及枝角类、桡足类和晶囊轮虫的密度均呈显著的正相关;2样点轮虫短后棘刺型个体各形态参数均随季节显著变化;长后棘刺型个体在1号样点内仅前外棘刺和后棘刺长有显著变化,而2号样点内仅体长、体宽和后棘刺长有显著变化;2样点内长后棘刺型个体的体长、体宽以及前外棘刺和后棘刺均显著长于短后棘刺型个体;同一形态型个体形态参数的样点间差异因季节的不同而异;短后棘刺型个体的前外棘刺和后棘刺长均与水体中总叶绿素a含量呈显著的正相关,后者与过滤水体中叶绿素a含量和枝角类密度也呈显著的正相关;长后棘刺型个体的后棘刺长与桡足类密度呈显著正相关,前内棘刺长与水温、溶氧量和晶囊轮虫密度呈显著负相关。两湖泊内剪形臂尾轮虫的后棘刺长和体长之间均呈显著的正相关,提示其后棘刺的延长并不是对体长的异速增长。     

Surface ultrastructure of Metagonimus takahashii metacercariae and adults

A scanning electron microscopic study was performed on the surface ultrastructure of metacercariae and adults of Metagonimus takahashii. Metacercariae were collected from the scale of crucian carp (Carassius auratus), and adult flukes were harvested 1-4 weeks after infection to rats. In excysted metacercariae, the oral sucker had type I (numerous) and type II (seven in total) sensory papillae. Tegumental spines were dense and digitated into 5-7 points on the surface anterior to the ventral sucker, but became sparse and less digitated posteriorly toward the end of the body. In adults, seven type II sensory papillae were characteristically arranged around the lip of the oral sucker, and on the inner side of the lip four small and two large type I sensory papillae were symmetrically seen on each side (12 in total). Tegumental spines on anterior two-thirds of the body, were digitated with 9-12 tips ventrally and 8-13 tips dorsally. Sperms entering into the Laurer's canal were observed. The results show that the surface ultrastructure of M. takahashii is generally similar to those of M. yokogawai and M. miyatai except for the digitation of tegumental spines.     

Surface ultrastructure of the developmental stages of Heterophyopsis continua (Trematoda: Heterophyidae).

Ultrastructural observations were made on the tegument of juvenile and adult stages of Heterophyopsis continua using scanning electron microscopy. On the surface posterior to the ventral sucker, the tegumental processes were bandlike in the metacercariae, cobblestonelike in the flukes 2 days postinfection (PI), and velvety at 3 days PI. The anterior surface between the oral and ventral suckers of the metacercariae was packed densely with tegumental spines having a 10- to 14-pointed tip. In flukes 6 days PI, the number of points increased to 15-17. The tegumental spines immediately behind the ventral sucker on the metacercariae surface possessed 5-7 points; posteriorly the points were reduced in size and in number. Ciliate sensory papillae (type I), as single or clumped forms of 2 or 3, were abundant around the oral and ventral suckers of metacercaria and adult worms. The clumped papillae appeared bilaterally symmetrical on the dorsal and ventral surfaces. The ciliate papillae may function in tango-, rheo-, and/or chemoreception. On the lip of the ventral sucker, 6-7 aciliate domed papillae (type II) were arranged in an equidistant manner. At 2 days PI each type II papilla became a clumped form having 2 or 3 papillae. Type II papillae may function as tango- and/or pressure-receptors. The structure and distribution of papillae suggest that the ventral sucker likely functions as a holdfast organ and the oral sucker as a probing organ involved in feeding.     

Surface ultrastructure of Heterophyes nocens (Trematoda: Heterophyidae).

The surface ultrastructure of Heterophyes nocens (Trematoda: Heterophyidae) was studied by scanning electron microscopy(SEM). The adult worms were recovered from experimentally infected cats and from a naturally infected patient. They were leaf-like, ventrally concave, and ovoid or pyriform in shape. Ciliated knob-like sensory papillae (type I) were observed in single or grouped forms on and around the oral sucker, whereas non-ciliated round swellings (type II papillae) were seen on the lip of the ventral sucker. The tegumental spines around the oral sucker were 5-9 pointed, whereas those between the two suckers were 12-17 pointed. Ventrolaterally, three groups of 5-6 type I papillae were located between the oral and ventral suckers, with single ones alternating between them. The genital sucker was protruded or depressed, depending on the contraction state of the flukes, and the gonotyl spine number ranged 50-60. The number of tip points of tegumental spines was decreased posteriorly; finally they became 1-3 pointed. On the dorsal surface, 4 groups of 4-5 type I papillae were symmetrically located on both lateral sides, and the shape and distribution of tegumental spines were similar to those of the ventral surface. Although the tegumental ultrastructure of H. nocens was generally similar to those of other heterophyids, the genital sucker morphology including the number of gonotyl spines and/or the distribution pattern of tegumental spines and sensory papillae were suggested to be the characteristic features of H. nocens.     

Fasciola gigantica: surface topography of the adult tegument

Adult Fasciola gigantica are leaf-shaped with tapered anterior and posterior ends and measure about 35 mm in length and 15 mm in width across the mid section. Under the scanning electron microscope its surface appears rough due to the presence of numerous spines and surface foldings. Both oral and ventral suckers have thick rims covered with transverse folds and appear spineless. On the anterior part of the ventral surface of the body, the spines are small and closely-spaced. Each spine has a serrated edge with 16 to 20 sharp points, and measures about 20 microm in width and 30 microm in height. In the mid-region the spines increase in size (up to 54 microm in width and 58 microm in height) and number, especially towards the lateral aspect of the body. Towards the posterior end the spines progressively decrease in both size and number. The tegumental surface between the spines appears highly corrugated with transverse folds alternating with grooves. At higher magnifications the surface of each fold is further increased with a meshwork of small ridges separated by variable-sized pits or slits. There are three types of sensory papillae on the surface. Types 1 and 2 are bulbous, measuring 4-6 microm in diameter at the base with nipple-like tips, and the type 2 also have short cilia. Type 3 papillae are also bulbous and of similar size but with a smooth surface. These sensory papillae usually occur in clusters, each having between 2 and 15 units depending on the region of the body. Clusters of papillae on the lateral aspect (usually types 1 and 2) and around the suckers (type 3) tend to be more numerous and larger in size. The dorsal side of the body exhibits similar surface features, but the spines and papillae appear less numerous and are smaller. Corrugation and invaginations of the surface are also less extensive than on the ventral side of the body.     

Fasciola hepatica: An immunofluorescent study of antigenic changes in the tegument during development in the rat and the sheep

Serum from sheep was collected throughout a 30-week period of infection with Fasciola hepatica and specificity for the tissues of flukes of various ages was tested by an indirect fluorescent antibody labeling technique, using as antigen JB4 plastic-embedded sections of flukes up to 30-weeks old grown in rats. Quantitative estimates of host antibody concentration and fluke tissue antigenicity were determined by titration using serially diluted serum. Serum from early infections (pre-7 weeks) gave strong labeling over the tegument of young flukes, but the reaction became progressively weaker with older fluke tissue. This was associated with a decline in the number of T1 bodies in the tegument as revealed by electron microscopy. T1 bodies contain glycocalyx precursor substances and during development they replace the antigenically similar T0 secretory bodies characteristic of early juvenile flukes. Glycocalyx turnover may help protect the pre-bile duct flukes against immunological attack. Serum from sheep with F. hepatica infections older than 7 weeks gave moderate reaction with T2 bodies which accumulated in the tegument during the early stages of infection but only expressed their antigens on the surface about the time of entry into the host's bile ducts. The antigenicity of the gut and excretory system of flukes seemed to remain unchanged throughout adult life. Levels of host antibody specific for juvenile tegument, gut, and excretory system peaked at 3–5 weeks postinfection, and declined once the flukes entered the bile ducts. Anti-T2 antibody appeared 6 weeks postinfection and began to decline 5–6 weeks later.     

Fasciola hepatica: IgG and IgA levels in the serum and bile of infected cattle

Bile and serum samples were collected from calves with an implanted cannula throughout a 20-week period of infection with Fasciola hepatica. Using indirect fluorescent antibody labelling and plastic-embedded sections of juvenile and adult flukes as antigens, estimates were made of the relative concentrations of IgG and IgA specific for fluke tegumental and gut antigens in the samples of serum and bile. In serum, antibodies against juvenile (t1) tegument and gut antigens reached peak concentrations 4–6 weeks postinfection and declined slowly thereafter as flukes became established in the bile ducts. IgG against adult tegument (t2) antigens appeared in the serum 6 weeks after infection, but no IgA against t2 was detected. In the bile, both IgG and IgA titres against t1 and gut antigens rose to peak values at 4–6 weeks after infection, but there was no activity against t2 antigen. The Ig levels in bile were considerably lower than in serum. Much more IgA relative to IgG occurred in bile as compared to serum (IgG/IgA ratio in serum was 16–32, in bile 1–2) suggesting a role for IgA in defence at mucosal surfaces. Comparison of the antibody profiles in bile and serum suggested that IgG in the bile was derived from circulating IgG whereas IgA may have been preferentially concentrated in the bile.     

Brachylaima cribbi (Digenea: Brachylaimidae): scanning electron microscopical observations of the life-cycle stages

Brachylaima cribbi is a recently described species of terrestrial trematode that infects mammals and birds with helicid land snails as its first and second intermediate hosts. The adult worm is 2.5-6.0 mm long by 0.5-0.8 mm wide being a long slender cylindrical worm with oral and ventral suckers in the anterior quarter and genital pore in the posterior quarter. Scanning electron microscopy shows that there is a dense covering of tegumental spines at the anterior end which diminishes towards the posterior extremities of the worm. Development of spines was observed in juvenile and mature adult worms. In young worms 1-3 weeks post infection (wpi) spines appear as buds with a serrated edge each having 1-4 spikes per spine. As the worm ages the spines broaden and by 5 wpi the number of spikes per spine increases to an average of 8.1. The serial development of oral sucker papillae in the cercaria, metacercaria and adult worm was observed with the finding of an elongated papilla with a bifurcated tip on the cercaria becoming a shorter and thicker elongated papilla with a large central stoma on the metacercaria. In the adult worm, this papilla becomes dome-shaped with a small central stoma. For some of these papillae a cilium could be seen extended from the central stoma. Other life-cycle stages illustrated were the hatched egg with an extruded egg membrane minus an operculum and a portion of the branched sporocyst dissected from the digestive gland of the land snail Theba pisana showing a terminal birth pore. Scanning electron microscopy morphological features of the adult worm observed for the first time in a Brachylaima were the unarmed cirrus extended from the genital pore with released sperm present and the Laurer's canal opening visible in tegumental folds on the dorsal surface approximately 300 microm posterior to the genital pore.     

土耳其斯坦东毕吸虫的扫描电镜观察

血吸虫类中如血居科(sanguinicolidae)的Aporocotyle simplex Odhner,1900、裂体科(Schistosomatidae)的日本血吸虫(Schistosoma japonicum)曼氏血吸虫(S.mansoni)及埃及血吸虫(S.haematobium)等多种血吸虫均经扫描电镜观察(Johnson and Moriearts,1969;Silk et al., 1969;Robson and Erasmus, 1970; Miller et al., 1972; Kuntz et al.,1976、1977;Voge et al., 1978; Thulin, 1980;及何毅勋和马金鑫,1980等)。关于土耳其斯坦东毕吸虫[Orientobitharzia lurkestanica(skrjabin,1913)Dut et Srivastava,1955]的体表扫描电镜尚无报告,而只见有此虫种体壁及肠管的透射电镜观察的资料(Lavrov and Fedoseenke,1978)。本文部分作者最近在内蒙东部兴安岭以南部分地区进行牛羊土     

Euryhelmis squamula (Digenea: Heterophyidae) Recovered from Korean Raccoon Dog,Nyctereutes procyonoides koreensis,in Korea

In this study, we intended to describe an unrecorded species of heterophyid trematode recovered from the small intestine of a Korean raccoon dog, Nyctereutes procyonoides koreensis, in Korea. A total of 13 small flukes were collected from a deceased Korean raccoon dog which was found in Chuncheon-si, Gangwon-do, Korea in May 2017. The trematode body were covered with many small spines, rectangular, broader than long, 807–1,103 μm long and 1,270–1,550 μm wide. Oral sucker in the anterior end slightly smaller than acetabulum. Pharynx muscular and well developed. Esophagus relatively long and sigmoid. Acetabulum small and located at median in anterior 2/5 portion. Ceca bifurcated at the anterior of genital pore and acetabulum and terminated at testis level. Testes larger, deeply lobed and located at the near of posterior end of body. Ovary small, triangular and located at the slight left of median and the anterior of left testis. Vitelline follicles dendritic and extend from the middle level of esophagus to the posterior portion of body. Eggs embryonated, operculated, small and 33–35×15–16 μm in size. Based on the morphological characteristics, the small heterophyid flukes recovered from the small intestines of Korean raccoon dog, N. procyonoides koreensis, were identified as Euryhelmis squamula (Digenea: Heterophyidae). Accordingly, this species of heterophyid flukes is to be a new trematode fauna in Korea by this study.     

Postembryonic development of Antygomonas incomitata (Kinorhyncha: Cyclorhagida)

Postembryonic development in the kinorhynch species Antygomonas incomitata was examined using scanning electron microscopy. The morphology of the six juvenile stages, J‐1 to J‐6, varies at numerous details, but they can also be distinguished by a few key characters. Juvenile stage 1 by its composition of only nine trunk segments; J‐2 by the combination of possessing 10 trunk segments, but no cuspidate spines on segment 9; J‐3 by the presence of cuspidate spines on segment 9, but only one pair of cuspidate spines on segment 8; J‐4 by the combination of 10 trunk segments only, but having two pairs of cuspidate spines on segment 8; J‐5 by possessing 11 trunk segments and same spine compositions as adults but is still maintaining postmarginal spiculae; J‐6 specimens closely resemble adults and are most easily identified by their reduced trunk lengths. New segments are formed in a growth zone in the anterior part of the terminal segment. The complete number of segments is reached in J‐5. Development of cuticular head and trunk structures are described through all postembryonic stages and following developmental patterns could be outlined: the mouth cone possesses outer oral styles from J‐1, but in J‐1 to J‐3, the styles alternate in size. Scalids of the introvert are added after each molt, and scalids appear earliest in the anterior rings, whereas scalids in more posterior rings are added in older postembryonic stages. The early J‐1 stage is poor in spines and sensory spots and both structures increase in number after each molt. The complete spine composition is reached in J‐4, whereas new sensory spots appear after all molts, inclusive the final one from J‐6 to adult. Sensory spots in the paraventral positions often appear as Type 3 sensory spots but are through development transformed to Type 2. This transformation happens earliest on the anterior segments. J. Morphol., 2010. © 2010 Wiley‐Liss, Inc.     

The musculature of horsehair worm larvae (<Emphasis Type="Italic">Gordius aquaticus</Emphasis>,<Emphasis Type="Italic"> Paragordius varius</Emphasis>, Nematomorpha): F-actin staining and reconstruction by cLSM and TEM

The musculature of larvae of Gordius aquaticus was investigated by laser-scanning microscopy and compared to transmission electron microscopic data for the larva of Paragordius varius. In the anterior portion of the body, the preseptum, four different muscle groups can be distinguished: (1) 12 anterior parietal muscles in the body wall, (2) six oblique muscles that function as retractors of the introvert, (3) six proboscideal muscles, which function as retractors for the proboscis, and (4) six muscles associated with spines of the outermost of the three rings of spines. The posterior portion of the body, the postseptum, possesses four pairs of longitudinal muscle strands in G. aquaticus, the postseptal parietal muscles, that are located dorsolaterally and ventrolaterally. These are not clearly visible in P. varius, where instead three pairs of parietal muscles are present. Additional small muscles are associated with the terminal spines and with the duct running from the pseudointestine to the body wall. All fibers show a cross-striated pattern although this striation is less obvious at the ends of the fibers.     

Comments on the morphology of the pre-oral spine in Argulus (Crustacea: Branchiura)

A histological study of the pre-oral spine and associated structures in Argulus japonicus reveals that two exceptionally long and slender muscles casuse retraction of the spine into the spinal sheath. Originating from the body wall mid-dorsally the two muscles proceed through the nerve ring and the blood-filled lumen of the spinal sheath before being inserted on a bolster of tissue constituting the base of the spine. Movement of the spinal sheath is affected by two muscles originating from a common apodeme in the dorsal body wall, just posterior to the nauplius eye, and inserted on the lateral walls of the base of the spinal sheath. Two ducts, each leading from a glandular complex in the lateral parts of the carapace, proceed rostrally through the haemocoelic spaces. After passing the tritocerebrum laterally they accompany the retractor muscles of the spine on their course to the base of the spine. Passing through the bolster of tissue at the base of the spine the two ducts run all the way up to the tip of the spine where they open separately. The glandula praeboscoidalis is not associated with the pre-oral spine since its duct runs posteriorly in the wall of the proboscis. The labial spines are associated with giant glandular cells located beneath the optic tracts. © 1992 Wiley-Liss, Inc.     

Suppressor of Cytokine Signalling 2 (SOCS2) Regulates Numbers of Mature Newborn Adult Hippocampal Neurons and Their Dendritic Spine Maturation

Overexpression of suppressor of cytokine signalling 2 (SOCS2) has been shown to promote hippocampal neurogenesis in vivo and promote neurite outgrowth of neurons in vitro. In the adult mouse brain, SOCS2 is most highly expressed in the hippocampal CA3 region and at lower levels in the dentate gyrus, an expression pattern that suggests a role in adult neurogenesis. Herein we examine generation of neuroblasts and their maturation into more mature neurons in SOCS2 null (SOCS2KO) mice. EdU was administered for 7 days to label proliferative neural precursor cells. The number of EdU-labelled doublecortin⁺ neuroblasts and NeuN⁺ mature neurons they generated was examined at day 8 and day 35, respectively. While no effect of SOCS2 deletion was observed in neuroblast generation, it reduced the numbers of EdU-labelled mature newborn neurons at 35 days. As SOCS2 regulates neurite outgrowth and dentate granule neurons project to the CA3 region, alterations in dendritic arborisation or spine formation may have correlated with the decreased numbers of EdU-labelled newborn neurons. SOCS2KO mice were crossed with Nes-CreER^T2/mTmG mice, in which membrane eGFP is inducibly expressed in neural precursor cells and their progeny, and the dendrite and dendritic spine morphology of newborn neurons were examined at 35 days. SOCS2 deletion had no effect on total dendrite length, number of dendritic segments, number of branch points or total dendritic spine density but increased the number of mature “mushroom” spines. Our results suggest that endogenous SOCS2 regulates numbers of EdU-labelled mature newborn adult hippocampal neurons, possibly by mediating their survival and that this may be via a mechanism regulating dendritic spine maturation.     

Tegumental ultrastructure of adult Gynaecotyla squatarolae (Digenea: Microphallidae)

Gynaecotyla squatarolae (Digenea: Microphallidae) adult flukes were recovered from experimental chicks at day 4-6 post-infection and their tegumental ultrastructure was observed with a scanning electron microscopy. They were pyriform in shape, and their anterior halves were concaved ventrally. The whole body surface was covered with tegumental spines, which were wide and 16-17 digitated between oral and ventral suckers. The density of spines and number of digits decreased posteriorly. The oral sucker was subterminal and the excretory pore was at the posterior end of the worm. Two ventral suckers were similar in appearance and protruded near midline of the worm. The genital atrium was dextral to the small ventral sucker. The dorsal surface was covered with tegumental spines, but the spines were sparser than on the ventral surface. On the middle portion of the dorsal surface, a small opening presumed to be the Laurer's canal was seen. From these findings, it has been confirmed that the adult G. squatarolae has unique characteristics in the surface ultrastructure.     

Surface ultrastructure of Metagonimus miyatai metacercariae and adults

A scanning electron microscopic study was performed to observe surface ultrastructures of excysted metacercariae and adults of Metagonimus miyatai. Metacercariae were collected from the scale of the pale chub (Zacco platypus), and adult flukes were harvested 1-4 weeks after infection to rats. In excysted metacercariae, the oral sucker was devoid of tegumental spines and had type I and type II sensory papillae. Anteriorly to the ventral sucker, spines were dense and digitated into 5-7 points, whereas near the posterior end of the body spines were sparse and digitated into 2-3 points. In one-week adults, 7 type II sensory papillae were arranged around the lip of the oral sucker, and at inner side of the lip one pair of small and two pairs of large type 1 sensory papillae were seen on each side. The distribution of tegumental spines was similar to that of metacercariae, but they were more differentiated with 9-11 pointed tips. In two- to four-week old adults, the surface ultrastructure was nearly the same as in one-week old adults, however, sperms were frequently seen entering into the Laurer''s canal. Conclusively, the surface ultrastructure of M. miyatai was generally similar to that of M. yokogawai, however, differentiation of tegumental spines and distribution of sensory papillae around the oral sucker were different between the two species, which may be of taxonomic significance.