The life-cycle of Echinostoma friedi n. sp. (Trematoda: Echinostomatidae) in Spain and a discussion on the relationships within the `revolutum' group based on cercarial chaetotaxy

The morphology of the different stages and life-cycle of Echinostoma friedi n. sp. are described and figured. The freshwater snail Lymnaea peregra (Gastropoda: Lymnaeidae) serves as the natural and experimental first intermediate host and L. corvus and Gyraulus chinensis (Gastropoda: Planorbidae) as experimental first intermediate hosts. These, and Physella acuta (Gastropoda: Physidae), also serve as second intermediate hosts. Adult worms, possessing 37 collar spines, were obtained from naturally infected Rattus norvegicus and experimentally from albino rats, golden hamsters and chickens. Mice were not suitable experimental definitive hosts. E. friedi differs from the most closely related species in the `revolutum' group mainly in terms of several morphological and biological features of the life-cycle stages and in its cercarial chaetotaxy. The chaetotaxy patterns of the species of the `revolutum' group are analyzed and the results show that a taxonomic comparison of these species may be carried out on the basis of the number of sensilla in the clusters CIII V₁, CIII V₂ (or CIII V₁ + CIII V₂), CIV DL and UV_b. These clusters appear adequate to establish taxonomic relationships between different species within the `revolutum' group.     

First record and description of metacercariae of Curtuteria arguinae n. sp. (Digenea: Echinostomatidae), parasite of cockles Cerastoderma edule (Mollusca: Bivalvia) in Arcachon Bay, France

A new Himasthlinae species, Curtuteria arguinae, is described as metacercariae from the cockle Cerastoderma edule (L.), collected at Banc d'Arguin (southwestern France). These metacercariae encysted preferentially in the mantle and also in the foot of cockles. Encysted and chemically excysted metacercariae were studied by light microscopy and scanning electron microscopy, respectively. Excysted metacercariae were elongated and curved ventrally. They bore a 33-spine circumoral collar. Sensory papillae were arranged around the oral sucker and also symmetrically along the ventral surface body, from the collar to the acetabulum. The dorsal and ventral tegument surfaces were densely packed with similar pointed spines. The posterior end of the body was without any spines. Among the Curtuteria species described previously, only Curtuteria haematopodis Smogorjewskaja and Iskova, 1966 had the same number of circumoral collar spines. A 6-yr field survey showed that the cockle population at Banc d'Arguin was subjected to a summer infection of C. arguinae. Curtuteria arguinae phenology of infection is characterized by interannual variability and seasonality (beginning in July-August and maximum in autumn). The first intermediate and final hosts remain unknown.     

The life cycle and transmission dynamics of the larval stages of Hypoderaeum conoideum

The morphology of the different larval stages and life cycle of Hypoderaeum conoideum (Trematoda: Echinostomatidae) are described. The freshwater snail species Lymnaea peregra (Gastropoda: Lymnaeidae) serves as the natural first intermediate host and this and L. corvus serve as experimental first intermediate hosts. These and other freshwater snails, such as Physella acuta and Gyraulus chinensis, in turn serve as second intermediate hosts. Adult worms were obtained from chicks and ducks, but not from rats, mice and golden hamsters. The morphology of the larval stages is compared with previous work on H. conoideum. Several aspects of the biology of the life history stages are described with emphasis on the transmission dynamics of the free-living stages. Differential suitability of the snail species that may act as first and/or second intermediate hosts is studied and discussed.     

Life cycle of Stephanoprora uruguayense (Digenea: Echinostomatidae) in Argentina

The life cycle of Stephanoprora uruguayense Holcman et Olagüe, 1989, was experimentally resolved. In an artificial pond in the Zoological Garden in Buenos Aires City, Argentina, Heleobia parchappei (Hydrobiidae) was found to be releasing large-tailed cercariae with a prepharyngeal body, but lacking collar spines and corpuscles in the excretory system. Metacercariae, which encysted on the gills of naturally and experimentally infected Cnesterodon decemmaculatus (Poecilidae), developed collar spines and corpuscles in the excretory system in 7 days. Sexually mature adults were recovered from chicks and immature adults from mice fed metacercariae from C. decemmaculatus. Eggs shed in chick feces developed to miracidia within 10 days; sporocysts were found on the gills of snails. Stephanoprora uruguayense and S. denticulata from Europe are similar in adult morphology, but can be distinguished by morphological and behavioral features of larvae. Likewise, although S. denticulata and S. paradenticulata from Venezuela are similar to S. uruguayense in adult morphology, they differ considerably in larval morphology and intermediate hosts.     

Morphological observations of Echinochasmus japonicus cercariae and the in vitro maintenance of its life cycle from cercariae to adults

The cercaria morphology of Echinochasmus japonicus was investigated using light and scanning electron microscopy. Cercariae, liberated from naturally infected snails (Parafossarulus manchouricus), had ovoid bodies and diminutive tails. The cercaria tegument was covered with minute spines. Four type II sensory papillae were observed on the dorsal side of the oral sucker, and type I papillae were distributed on the dorsal tegument surfaces. When cercariae were kept in the same bath as the freshwater fish, Pseudorasbora parva, which were free from trematode infections, parasites encysted only in the gills of fishes at day 4 postinfection (PI). The outermost metacercaria wall was fully formed in host tissues at day 7 PI. Adult worms were recovered from the intestines of rats, chicks, and ducks 28 days after experimental exposure to metacercariae. The head crown of the adult was armed with 24 collar spines, which were interrupted dorsal to the oral sucker, and the species was identified as E. japonicus.     

Life-cycle ofEchinochasmus macrocaudatus n. sp. (Trematoda: Echinostomatidae)

The life-cycle ofEchinochasmus macrocaudatus n. sp., from mother-sporocyst to adult, was studied under natural and experimental conditions. The aquatic snailsPyrgophorus coronatus (Prosobranchia: Hydrobiidae) from cenotes (sinkholes) of the Yucatan Peninsula, Mexico, served as the first intermediate host of this parasite, liberating cercariae possessing an extremely large tail (zygocercous cercaria). Metacercariae of the fluke were encysted on the gills of the characid fishAstyanax fasciatus (natural infection); the poeciliidsXiphophorus variatus andPoecilia velifera were suitable experimental hosts. Feeding experiments withE. macrocaudatus metacercariae resulted in finding adult trematodes, possessing 22 collar spines (with 2 angle spines on each side), in the intestine of chicks and ducks.E. macrocaudatus differs from the most closely related species,E. schwartzi Price, 1931, by its larger oral sucker (138–170×118–176 m) and by the position of the acetabulum which is situated at two-fifths of the body length.     

Corbicula fluminea (Bivalvia: Corbiculidae): a possible second molluscan intermediate host of Echinostoma cinetorchis (Trematoda: Echinostomatidae) in Korea.

More than 1,500 clams of Corbicula fluminea, the most favorable food source of freshwater bivalves in Korea, were collected from 5 localities to examine cercarial and metacercarial infection with Echinostoma cinetorchis. Although 3 clams infected with suspicious E. cinetorchis metacercariae out of 200 specimens collected at Kangjin, Chollanam-do were detected, no cercarial and metacercarial infections with E. cinetorchis were observed in field-collected Corbicula specimens. In the susceptibility experiments with laboratory-reared clams, those infected with miracidia of E. cinetorchis did not release their cercariae up to 60 days after infection. To confirm the identity of second intermediate host of E. cinetorchis experimentally, a total of 30 clams were exposed to the cercariae from Segmentina hemisphaerula that had been infected with miracidia of E. cinetorchis. The clams were susceptible to cercariae of E. cinetorchis with an infection rate of 93.3%. Metacercariae from clams taken more than 7 days after cercarial exposure were fed to rats (S/D strain), and adult worms of E. cinetorchis, characterized by 37-38 collar spines on the head crown, were recovered from the ileocecal regions. This is the first report of C. fluminea as a possible second intermediate host of E. cinetorchis.     

Echinostoma macrorchis in Lao PDR: Metacercariae in Cipangopaludina Snails and Adults from Experimentally Infected Animals

The echinostome metacercariae encysted in Cipangopaludina sp. snails that were purchased from a market in Vientiane Municipality, Lao PDR, were identified as Echinostoma macrorchis (Digenea: Echinostomatidae) through recovery of adult flukes after experimental infection to rats and a cat. The metacercariae were round, 113-128 (121)×113-125 (120) µm, having a thick cyst wall, a head collar armed with collar spines, and excretory granules. The adult flukes recovered from the rats and cat at day 14 and 30 post-infection, respectively, were elongated, ventrally curved, and 3.9-6.3×0.7-1.1 mm in size. The head collar was distinct, bearing 43-45 collar spines with 5 angle spines on each side. Two testes were large (as the name implies), tandem, and slightly constricted at the middle, with irregular margins. Eggs were operculated, ovoid to elliptical, and 88-95×56-60 µm. In scanning electron microscopy, the head collar was prominent, with 43-45 collar spines. Scale-like tegumental spines were densely distributed on the ventral surface between the oral and ventral suckers. Sensory papillae were distributed mainly on the tegument around the 2 suckers. It is confirmed that E. macrorchis is distributed in Lao PDR using Cipangopaludina sp. snails as the second intermediate host.     

Scanning electron microscopy of adult Echinoparyphium recurvatum (Von Linstow, 1873) (Digenea: Echinostomatidae) from Britain

The surface topography of 15-day-old adult Echinoparyphium recurvatum (Von Linstow, 1873) sensu stricto, from an isolate of the parasite utilizing Lymnaea peregra as first intermediate host in southern England, is described and illustrated using scanning electron microscopy, and is compared to those of other Echinoparyphium species from Europe, and with those of E. recurvatum of East Asian origin. The general morphology of tegumental features was found to be very similar to that of worms of the same age observed in a previous study on a Korean isolate of E. recurvatum. Comparison of collar and body spination of E. recurvatum with other 45-collar-spined members of the genus in Europe revealed some significant differences in morphology. Collar spines of E. recurvatum were found to be shorter and more pointed than those of Echinoparyphium mordwilkoi. The body spines of E. recurvatum are rounded and scale-like, extending just beyond the ventral sucker, contrasting with the pointed, thorn-shaped body spines of E. mordwilkoi, extending posteriorly to the level of the second testis. Body spine shape and distribution in E. recurvatum were found to be more similar to those of Echinoparyphium pseudorecurvatum. The value of SEM studies in elucidating the relationship between members of the genus Echinoparyphium in Britain/Europe and those in Africa, Asia and North America is suggested.     

Cipangopaludina chinensis malleata (Gastropoda: Viviparidae): a new second molluscan intermediate host of a human intestinal fluke Echinostoma cinetorchis (Trematoda: Echinostomatidae) in Korea

Two species of the viviparid snails have been reported in Korea, e.g., Cipangopaludina chinensis malleata and Cipangopaludina japonica. Cipangopaludina chinensis malleata collected at 3 of 12 localities were found to be infected with metacercariae of Echinostoma cinetorchis, one of the snail-borne human intestinal trematodes in Korea. Metacercariae from these snails were fed to rats (S/D strain), and adult worms of E. cinetorchis, characterized by 37-38 collar spines on the head crown, were recovered from the ileocecal regions. However, no C. japonica collected from 2 localities harbored the metacercariae. In experiments with laboratory-bred viviparid snails, all viviparids were not susceptible to miracidia of E. cinetorchis. To confirm the identity of second intermediate hosts of E. cinetorchis experimentally, 2 species of viviparid snails were exposed to the cercariae from Segmentina hemisphaerula that had been infected with miracidia of E. cinetorchis. Both species of snails were susceptible to cercariae of E. cinetorchis. This is the first report of Cipangopaludina spp. serving as the second intermediate host of E. cinetorchis and as a potential source of human infection.     

Echinostoma luisreyi n. sp. (Platyhelminthes: Digenea) by light and scanning electron microscopy

The entire life cycle of the Brazilian Echinostoma luisreyi n. sp., of the 37-collar spine E. revolutum group, has been observed under experimental conditions. The snail Physa marmorata serves as its first natural intermediate host. This species and the planorbid Biomplalaria glabrata act as experimental second intermediate hosts. The worm recovery rate was 51.3 and 0.6% for mice and hamsters, respectively, but the infection did not develop in the quail Coturnix coturnix. The natural vertebrate host is not known. The most important morphological character of the new species separating it from the other Echinostoma species studied is the oral corner spines that increase in size from the latero-oral to the ventro-oral regions. The ratio of the sizes of the smaller oral spines and the larger aboral ones was 1.7:1.0. Also, the excretory pore is radially wrinkled and dorsally subterminal. Images obtained by scanning electron microscopy confirmed the characters that differentiate the new species and the most closely related species.     

Life-cycle,delimitation and redescription of Echinostoma revolutum (Froelich, 1802) (Trematoda: Echinostomatidae)

The life-cycle of Echinostoma revolutum (Froelich, 1802) Dietz, 1909 has been completed experimentally beginning with infected snails collected at the type-locality, near Erlangen, Germany. Based on the specimens obtained, each stage of the life-cycle has been redescribed. Important taxonomic features are discussed and hitherto unknown characteristics are described. Synonyms for E. revolutum are: Fasciola revoluta Froelich, 1802; Echinostoma paraulum Dietz, 1909; E. audyi Lie & Umathevy, 1965; and E. ivaniosi Mohandas, 1973. Adults and larvae described as E. revolutum in other works are found to be identical with Echinostoma echinatum (Zeder, 1803), E. trivolvis (Cort, 1914), E. jurini (Skvortsov, 1924), E. caproni Richard, 1964, Moliniella anceps (Molin, 1859), Echinochasmus beleocephalus (Linstow, 1873) and other echinostome species. For nearly a century, incorrect morphological, biological, life-cycle and host information has been attributed to E. revolutum, and at times these data have contributed to the diagnoses of the species. Occasionally, authors actually working with E. revolutum have ascribed their results to other species. Based on extensive experimental life-cycle studies beginning with infected snails from type-localities, it is shown that (1) the first intermediate host is a lymnaeid snail; (2) the second intermediate hosts are various pulmonate and prosobranch snails, mussels, frogs and freshwater turtles; (3) the final hosts are birds; (4) E. revolutum cercariae and adults have 37 collar spines; (5) the species occurs only in Europe and Asia; (6) Cercaria echinata Siebold, 1937, Echinostoma echinatum (Zeder, 1803) and E. jurini (Skvortsov, 1924) are the closely related 37-spined allies in Europe; and (7) species specific characteristics are expressed only in the larvae and the host-parasite relationships. The adults of E. revolutum cannot be identified using morphological criteria and it is proposed that worms with 37 collar spines belonging to the genus Echinostoma and occurring in naturally infected birds in Europe and Asia be referred to an “E. revolutum group.”     

<Emphasis Type="Italic">Petasiger islandicus</Emphasis> n. sp. (Digenea: Echinostomatidae) in the horned grebe <Emphasis Type="Italic">Podiceps auritus</Emphasis> (L.) (Aves: Podicipedidae) from Iceland

Petasiger islandicus n. sp. is described and figured from a demographically isolated population of the horned grebe Podiceps auritus auritus (L.) in Lake Myvatn (Iceland). This new species belongs to the group of species with 19 collar spines which possess a large elongate-oval cirrus-sac, well-developed pars prostatica and massive bulb-like cirrus. Within this group, P. islandicus appears most similar to P. oschmarini Kostadinova & Gibson, 1998, a form with similar body dimensions described from the same host, but differs in having a larger head collar, collar spines, oral sucker, pharynx, testes and sucker-width ratio, and a smaller cirrus-sac, cirrus and eggs. Two Nearctic species resemble P. islandicus in general morphology but differ as follows: P. pseudoneocomense Bravo-Hollis, 1969 has a larger body and collar width, notably shorter collar spines, smaller testes and sucker-width ratio, and a shorter but much wider cirrus-sac which is also smaller relative to the ventral sucker and almost entirely anterior to it; and P. caribbensis Nassi, 1980 has a smaller body, shorter collar spines and a seminal vesicle which is small in relation to the cirrus-sac, vitelline fields reaching anteriorly to the level of the genital pore and the intestinal bifurcation is located more anteriorly.     

Production and chronobiology of emergence of the cercariae of Euparyphium albuferensis (Trematoda: Echinostomatidae)

The production and the chronobiology of emergence of the cercariae of Euparyphium albuferensis from Gyraulus chinensis experimentally infected with a single miracidium were established during 28 consecutive days from the first day of cercarial shedding. Moreover, the effect of a sudden change in light-dark cycling was investigated. Although the daily cercarial shedding rates show great variability, a progressive increase in cercarial production was observed in the first weeks of the cercarial shedding periods, probably in relation to the demography of intramolluscan larval stages. Under 12:12 light-dark cycling conditions, E. albuferensis cercariae emerged in the light, and the rhythm was circadian. The sudden change in the light-dark cycle resulted in corresponding alterations in emergence patterns, which shows that cercarial emergence was correlated to light-dark alternation. The ecological consequences of daily emergence by mobile cercariae whose target hosts are organisms that regularly occur in the same habitat with the molluscan emitting host, such as those of E. albuferensis, are discussed with reference to the hypotheses proposed to date, and an alternative hypothesis is proposed.     

Echinostoma mekongi: Discovery of Its Metacercarial Stage in Snails,Filopaludina martensi cambodjensis,in Pursat Province,Cambodia

Echinostoma mekongi was reported as a new species in 2020 based on specimens collected from humans in Kratie and Takeo Province, Cambodia. In the present study, its metacercarial stage has been discovered in Filopaludina martensi cambodjensis snails purchased from a local market nearby the Tonle Sap Lake, Pursat Province, Cambodia. The metacercariae were fed orally to an experimental hamster, and adult flukes were recovered at day 20 post-infection. They were morphologically examined using light and scanning electron microscopes and molecularly analyzed by sequencing of their mitochondrial cox1 and nad1 genes. A total of 115 metacercariae (1–8 per snail) were detected in 60 (60.0%) out of 100 Filopaludina snails examined. The metacercariae were round, 174 μm in average diameter (163–190 μm in range), having a thin cyst wall, a head collar armed with 37 collar spines, and characteristic excretory granules. The adult flukes were elongated, ventrally curved, 7.3 (6.4–8.2)×1.4 (1.1–1.7) mm in size, and equipped with 37 collar spines on the head collar (dorsal spines in 2 alternating rows), being consistent with E. mekongi. In phylogenetic analyses, the adult flukes showed 99.0–100% homology based on cox1 sequences and 98.9–99.7% homology based on nad1 sequences with E. mekongi. The results evidenced that F. martensi cambodjensis snails act as the second intermediate host of E. mekongi, and hamsters can be used as a suitable experimental definitive host. As local people favor to eat undercooked snails, these snails seem to be an important source of human infection with E. mekongi in Cambodia.     

An ectosymbiotic flatworm, Temnocephala chilensis, as second intermediate host for Echinoparyphium megacirrus (Digenea: Echinostomatidae) in Patagonia (Argentina)

During a survey of parasites of the Patagonian freshwater crab Aegla neuquensis neuquensis, its ectosymbiont Temnocephala chilensis was found parasitized with an echinostomatid metacercaria with 43 collar spines. Of the 414 T. chilensis collected, 106 were parasitized with metacercariae of Echinoparyphium sp. Ovigerous adults of E. megacirrus were obtained from domestic chicks experimentally infected with metacercariae obtained from temnocephalans. This is the first record of temnocephalans being parasitized by digeneans.     

Echinostoma echinatum (Zeder 1803) sensu Kanev (Digenea: Echinostomatidae): a note of caution

The re-examination of the voucher specimens identified by Kanev et al. (1987) as E. echinatum (Zeder, 1803) showed that two distinct species have been considered as E. echinatum: E. sarcinum Dietz, 1909, possessing 47 collar spines [Lymnaea truncatula strain — set ‘L’ (No. 326 TB)] and Echinostoma sp. (?echinatum) with 37 collar spines [Planorbis planorbis strain — set ‘P’ (No. 327 TB)]. The material of E. sarcinum is described and differentiated from E. revolutum and E. echinatum (sensu Kanev, 1985). The present results suggest that species identity of the material described as E. echinatum in Kanev's (1985) experimental study requires further clarification.