Himasthla Quissetensis Research Articles

Himasthla spp. (Trematoda) In The Edible Cockle Cerastoderma edule: Review, Long-Term Monitoring And New Molecular Insights.

AbstractTrematodes are the main macroparasites in coastal waters. The most abundant and widespread form of these parasites is metacercaria. Their impact on their host fitness is considered relatively low but metacercarial larvae of some species can have deleterious effects on individuals and/or populations. This review focused on the cockle Cerastoderma edule and four species of the genus Himasthla; a common host–parasite system in marine coastal environments. Our aims were (1) to review literature concerning Himasthla continua, Himasthla elongata, Himasthla interrupta and Himasthla quissetensis in cockles; (2) to provide molecular signatures of these parasites and (3) to analyse infection patterns using a 20-year monthly database of cockle monitoring from Banc d'Arguin (France). Due to identification uncertainties, the analysis of the database was restricted to H. interrupta and H. quissetensis, and it was revealed that these parasites infect cockles of the same size range. The intensity of parasites increased with cockle size/age. During the colder months, the mean parasite intensity of a cockle cohort decreased, while infection occurred in the warmest season. No inter-specific competition between trematode parasites was detected. Furthermore, even if the intensity of H. interrupta or H. quissetensis infection fluctuated in different years, this did not modify the trematode community structure in the cockles. The intensity of infection of both species was also positively correlated with trematode species richness and metacercarial abundance. This study highlighted the possible detrimental role of Himasthla spp. in cockle population dynamics. It also revealed the risks of misidentification, which should be resolved by further molecular approaches.

First documentation and molecular confirmation of three trematode species (Platyhelminthes: Trematoda) infecting the polychaete Marenzelleria viridis (Annelida: Spionidae).

Polychaete worms are hosts to a wide range of marine parasites; yet, studies on trematodes using these ecologically important species as intermediate hosts are lacking. During examination of the spionid polychaete Marenzelleria viridis collected on the north shore of Long Island, New York, putative trematode cysts were discovered in the body cavity of these polychaetes. In order to verify these cysts as metacercariae of trematodes, specimens of the eastern mudsnail Ilyanassa obsoleta (a very common first intermediate host of trematodes in the region) were collected for molecular comparison. DNA barcoding using cytochrome C oxidase I regions confirmed the presence of three species of trematodes (Himasthla quissetensis, Lepocreadium setiferoides, and Zoogonus lasius) in both M. viridis and I. obsoleta hosts. Brown bodies were also recovered from polychaetes, and molecular testing confirmed the presence of L. setiferoides and Z. lasius, indicating an immune response of the polychaete leading to encapsulation of the cysts. From the 125 specimens of M. viridis collected in 2014, 95 (76.8 %) were infected with trematodes; of these 95 infected polychaetes, 86 (90.5 %) contained brown bodies. This is the first confirmation that trematodes use M. viridis as a second intermediate host and that this intermediate host demonstrates a clear immune response to metacercarial infection. Future research should explore the role of these polychaetes in trematode life cycles, the effectiveness of the immune response, and transmission pathways to vertebrate definitive hosts.

Cockle infection by Himasthla quissetensis – I. From cercariae emergence to metacercariae infection

The European cockle (Cerastoderma edule) is an exploited bivalve along the North-Eastern Atlantic semi-sheltered ecosystems. Its population dynamics are driven by numerous environmental factors, including parasitism, particularly by trematodes. The complex life cycle of trematodes includes a free living stage (cercaria) between the first (a mollusk) and the second (an invertebrate or a vertebrate) intermediate hosts. Taking the example of Himasthla quissetensis, a dominant trematode in Arcachon Bay (France) utilizing Nassarius reticulatus as first intermediate host and the cockle as second intermediate host, we investigated the correlation between cockle infection and cercariae emergence by N. reticulatus, including the role of water temperature and light. Experimental and field data provided evidence that cercariae emergence from N. reticulatus took place during the night and for water temperature comprised between 15°C and 22°C (optimum at 20°C). The lifespan of cercariae did not exceed 48h and 50% of them were no more infectious after 7h. A model was designed (emergence=f(water temperature)) in order to calculate an average monthly cercarial emergence rate according to water temperature that was daily recorded for 5years (1998–2002). Concomitantly, non-infected cockles were transplanted each of these years in order to assess the infection rate by H. quissetensis. Infection occurred strictly for the same water temperatures (and dates) as those expected for cercariae emergence. Within each year, there was often (but not always) a good correlation between the predicted number of emerging cercariae and the observed number of cercariae transformed into metacercariae in cockles. However, the among-years variability of cockle infection (×4.4 range) was not explained by the predicted annual number of emerging cercariae. This study highlights the importance of water temperature and light in stimulating cercariae emergence which is closely related to the occurrence of cockle infection. Accordingly, climate change would be expected to alter certain parasite transmission traits. Conversely, the lack of correlation between the total number of metacercariae in cockles and the expected number of cercariae suggests that other factors contribute to infestation variability.

Cockle infection by Himasthla quissetensis — II. The theoretical effects of climate change

Numerous marine populations experience parasite pressure. This is the case of the cockles Cerastoderma edule which are often highly infected by trematode macroparasites. These parasites display a complex life cycle, with a succession of free-living and parasitic stages. Climate, and in particular temperature, is an important modulator of the transmission dynamics of parasites. Consequently, global change is thought to have implications for the epidemiology of infectious diseases. Using Himasthla quissetensis, a dominant parasite of cockles as 2nd intermediate host in Arcachon Bay (France), we used mathematical models of parasite emergence (cercariae) and parasite infection (metacercariae) in cockles as a function of water temperature, in order to study different scenarios of temperature increases. Globally, with a +0.5°C to +6.0°C simulation, cumulated emergence of cercariae and accumulation of metacercariae tended to decrease or stagnate, respectively. This is the consequence of a trade-off between sooner (spring) and later (autumn) cercariae emergence/infestation on one hand, and a longer inhibition period of cercariae emergence/infestation during the hottest days in summer. Using sea water temperature in Oualidia (Morocco) where mean annual sea temperature is 3°C higher than in Arcachon Bay, our model predicted infestation all year long (no seasonality). The model gave a correct estimation of the total number of parasites that was expected in cockles. Conversely, observed infestation in Oualidia followed a seasonal pattern like in Arcachon Bay. These results suggest that, if temperature is a strong driver of parasite transmission, extrapolation in the framework of climate change should be performed with caution.

Host Quality and Spatial Patterning in Infections of the Eastern Mudsnail (Ilyanassa obsoleta) by Two Trematodes (Himasthla quissetensis and Zoogonus rubellus)

Several studies have suggested that the fitness of a parasite can be directly impacted by the quality of its host. In such cases, selective pressures could act to funnel parasites towards the highest-quality hosts in a population. The results of this study demonstrate that snail host quality is strongly correlated with spatial patterning in trematode infections and that habitat type is the underlying driver for both of these variables. Two trematodes (Himasthla quissetensis and Zoogonus rubellus) with very different life cycles assume the same spatial infection pattern in populations of the first intermediate host (Ilyanassa obsoleta) in coastal marsh habitats. Infected snails are disproportionately recovered from intertidal panne habitats, which offer more hospitable environs for snails than do adjacent habitats (intertidal creeks, coastal flats, and subtidal creeks), in terms of protection from turbulence and wave action, as well as the availability of food stuffs. Snails in intertidal panne habitats are of higher quality when assessed in terms of average size-specific mass, growth rate, and fecundity. In mark-recapture experiments, snails frequently dispersed into intertidal pannes but were never observed leaving them. In addition, field experiments demonstrate that snails confined to intertidal panne habitats are disproportionately infected by both trematode species, relative to conspecifics confined to adjacent habitats. Laboratory experiments show that infected snails suffer significant energetic losses and consume more than uninfected conspecifics, suggesting that infected snails in intertidal pannes may survive better than in adjacent habitats. We speculate that 1 possible mechanism for the observed patterns is that the life cycles of both trematode species allows them to contact the highest-quality snails in this marsh ecosystem.

Assessment of Digenean Parasitism in Nassarius reticulatus (L.) along the Portuguese Coast: Evaluation of Possible Impacts on Reproduction and Imposex Expression

A survey was performed between June and September 2006 along the Portuguese coast to assess the prevalence of digenean parasitism in the netted whelk Nassarius reticulatus, a bioindicator of tributyltin (TBT) pollution. It was also intended to evaluate the effect of parasites on the reproduction of this gastropod species and their interference on the development of imposex (the superimposition of male characters onto prosobranch females) and male penis, based on field data. Five digenean species (Lepocreadium album, Gynaecotyla longiintestinata, Himasthla quissetensis, Diphtherostomum brusinae, and Cardiocephalus longicollis), plus 1 unidentified species, were found to infect N. reticulatus. Parasitism was spread along the Portuguese coast, but the higher values of prevalence were found in sheltered inshore areas where up to 67.4% of the animals were affected per sampling station. Parasitism has a castrating impact on the whelks and a reducing effect on male penis size, which causes serious disorders in the reproduction of N. reticulatus and may have an important impact in its population dynamics. However, no relationship between imposex severity and parasite infestation was found.

Larval trematode infections and spatial distributions of snails

Abstract. The hypothesis that infecting trematodes influence the spatial distribution of the estuarine snail Ilyanassa obsoleta was tested. This work was conducted in the Savages Ditch habitat, Rehoboth Bay, DE, USA, which has an essentially flat, sandy‐mud bottom bordered by saltmarsh shorelines and many infected snails. In 1996, two groups of snails were individually marked and released from one location after being screened for trematode infections. One group, transplanted from sites where snails tended not to be infected, consisted of snails that tested as uninfected. The other group consisted of snails native to Savages Ditch. Species of trematode carried by each snail was recorded. Marked snails were found and their positions were recorded until 2001. Snails were in five infection categories: (1) not infected, and infected with (2) Himasthla quissetensis, or (3) Lepocreadium setiferoides or (4) Zoogonus rubellus, or (5) with both H. quissetensis and Z. rubellus. The results show that the spatial distributions of snails depended on whether or not they were infected and, if infected, on which trematode species they carried. To complete life cycles, these parasites must accomplish transmission from the first (the snail) to the second intermediate hosts by short‐lived, swimming cercariae. These data do not allow resolution of why snails distributed as they did, but sighting distributions of infected snails can be related to distributions of second hosts and it is proposed that parasites engender host snail distributions that improve chances of transmission.

Cockle Cerastoderma edule population mortality: role of the digenean parasite Himasthla quissetensis

Infection patterns of the digenean trematode Himasthla quissetensis in its second inter- mediate host, the edible cockle Cerastoderma edule, and the impact of this parasite on cockle popula- tions were quantified. A 2 yr transplant experiment and a 4 yr survey were conducted in Arcachon Bay, a coastal lagoon on the Atlantic SW coast of France. Cockles free of H. quissetensis were trans- planted at La Canelette, a station where cockles were usually highly infected. Infection began in May, when the water temperature reached 17°C and stopped in November (12°C). There was no new infec- tion between November and April. Monthly surveys at 2 stations, Arguin and La Canelette, confirmed that cockle infection by H. quissetensis occurred during the warmer period of the year. Only cockles with a shell length > 8 mm became infected; therefore, cockle growth rate, which differed at the 2 sta- tions, was also a key factor explaining infection phenology. In winter, the mean parasite abundance of H. quissetensis in cockles decreased at both stations. The mortality rate of parasites in cockles was very low, with no seasonal pattern, and did not explain this winter decrease. Consequently, the decrease of H. quissetensis was interpreted as mortality of heavily infected cockles. At Arguin, where the cockle population was characterised by moderate abundance, high growth rate and short lifespan, cockle mortality amounted to 93% during the first year of benthic life, with no significant contribution of parasites; in the following year (Year 2), cockle mortality was 85%, with 28% due to H. quissetensis infection. At La Canelette, the cockle population, characterised by low abundance and low growth rate, suffered almost 100% mortality in the first year, with no contribution by parasites, which started to infect cockles in the second year only; the remaining cockles had a long lifespan (up to 5 yr), and >46% of their mortality was linked to H. quissetensis infection. It is concluded that both host growth rate and water temperature are important factors in the initiation of parasite infection and that the intensity of infection and its effect on host mortality closely depend on host growth and environmental factors.

Tenure of individual larval trematode infections in an estuarine gastropod

Ilyanassa obsoleta(Mollusca: Gastropoda) is an abundant inhabitant of salt marshes and tidal flats on the east coast of North America. Populations of this snail may be heavily infected by larval trematodes. Three species were observed in this work,Himasthla quissetensis, Lepocreadium setiferoides, andZoogonus rubellus. Mostly as single-species infections, all occupy snail tissues as parthenitae that produce cercariae, which are released from the snail to infect the next host. By periodically testing snails for cercarial emission, single-species infections are here shown to persist over six summers and double-species infections are also noted to be long-lived. Among the 32 snails followed, 25 released the same (or no) cercariae throughout observation periods averaging three years. The other seven indicated infection changes, but only two of these are judged to reflect actual changes. The probability that a snail changed infection status in this study is thus 2.1% y−1.Ilyanassa obsoletaindividuals, and apparently their trematode infections, can persist for decades. Because species colonize and get evicted infrequently, sets of trematode species infecting I.obsoletaindividuals (infracommunities) are concluded to be isolationist in character.

Cockle emergence at the sediment surface: 'favourization' mechanism by digenean parasites?

The aim of the present work was to assess the effect of digenean trematodes on indirect mortality of the cockle Cerastoderma edule, an infaunal bivalve. The tested hypothesis was that parasites altered the burrowing capacity of cockles and thus exposed them at the sediment surface, where they are more vulnerable to predators. If the predator is the final host, this mechanism, which drives the cockle out of the sediment, is considered as a 'favourization'. Cockle populations from 2 stations in Arcachon Bay (France)-Banc d'Arguin (oceanic situation) and La Canelette (lagoonal situation)--were sampled for 1 yr. At La Canelette, monitoring every 2 d showed that 50% of adult cockles regularly migrated to the sediment surface at a rate of 5 cockles m(-2) yr(-1) and disappeared in a few days. In the laboratory, 67% of these 'surface cockles' did not burrow again, suggesting that they would die in the field. Moreover, mortality measured after 7 d in the laboratory was 2 to 5 times higher than mortality of 'buried cockles', at both stations and particularly during summer. Species richness and abundance of digeneans from both stations were compared in 'buried' and 'surface' individuals to determine whether parasites played a role in cockle migration and mortality. Ten and 9 digeneans were found at Banc d'Arguin and La Canelette, respectively, with Himasthla quissetensis and Labratrema minimus being the most prevalent and abundant species at both stations. The abundance of H. quissetensis was slightly higher in surface cockles at Banc d'Arguin, but the difference fluctuated with station and cockle age (or size). L. minimus prevalence was only higher in surface cockles at La Canelette. In the latter station, we estimated that L. minimus and H. quissetensis were responsible for the emergence of 9 and 2%, respectively, of the buried cockles. Although this favourization mechanism may induce some mortality in cockles, it does not alone explain the magnitude of the observed mortalities (41 and 57% at La Canelette and Banc d'Arguin, respectively). A correspondence analysis did not show the presence of a particular parasite community in buried or surface cockles, which could explain these high surface cockle mortalities in association with the 2 dominant digeneans.

Trematode Accumulation by the Estuarine Gastropod Ilyanassa obsoleta

The accumulation of larval trematodes by Ilyanassa obsoleta (Gastropoda) at 2 estuarine sites in Delaware was studied. Initial infection status of snails was assayed by looking for shed cercariae. Native snails (most already infected) were deployed at sites A and B, and sentinel snails (putatively uninfected) were deployed at site B. All were individually marked and, if found, reassessed for infection after being free 1-3 summers. Himasthla quissetensis, Lepocreadium setiferoides, Zoogonus rubellus, Austrobilharzia variglandis, and Gynaecotyla adunca infections were observed in recovered snails. At site A, in 1993, 62 natives were recovered. Among the 26 initially testing uninfected, 15 had infections at recovery. Of 36 that released cercariae, 26 had the infection initially indicated. Of sentinels released at site B in 1996, 3 of 16 had infections when recollected. One probably was infected before transplant; at least 2 were infected at site B during 1996-1997. Among site B natives, 26 were later examined by dissection in 1996; 22 had the infection status initially revealed. Some site B natives (n = 35) escaped recapture in 1996 but were found in 1997, or 1998, or both, and were reexamined, most by cercarial release. The same cercariae were produced by 30. Among natives (both sites, n = 123), 27.6% exhibited some difference in infection status compared to the initial assay. This probably overestimates changes. Some differences were real but most can be discounted as cases where initial infection status was misrepresented.

Ilyanassa obsoleta (Gastropoda) as a Host for Trematodes in Delaware Estuaries

Extensive data characterizing larval trematode communities in marine gastropods do not exist for many systems. The purpose here is to report on the infections encountered in Delaware Ilyanassa obsoleta and to compare this trematode community with certain others that have been well studied. Over 15 yr, 11,774 I. obsoleta from 9 different estuarine habitats were examined. Trematode parasitism, sex, and size were determined for each snail. In the total collection, 9 trematode species were encountered; 51.04% of snails were infected with 1 or more species. The sexes were equally susceptible to being parasitized. Smaller snails were less likely to be infected than larger ones. Juvenile snails can be infected, but few have been colonized because of the short time they have been exposed to infective stages. Other studies of trematodes in this snail have revealed few multispecies infections. In contrast, they were strikingly common in this study (12.57% of all snails). Himasthla quissetensis seldom infects the same snail with Lepocreadium setiferoides or Austrobilharzia variglandis, but other species combinations can coexist. The important element in this trematode community seems to be time. The observed frequencies of different infracommunities (single and multispecies combinations) in samples of snails are considered to result from a variety of causes. These include commonness of the trematode species in the system, where and how the sample was collected, definitive host behavior, the low probability of a snail becoming infected, the long life of the snail and its infections, the vagility of the snail, and the incompatibility of certain species in terms of infecting the same snail.

Trematode infections in a gastropod host misrepresented by observing shed cercariae

Cercarial emergence is often used to determine trematode infections in gastropods. Specimens of Ilyanassa obsoleta (Say) ( n = 206) were examined for trematode infections by two methods, cercarial emergence and dissection. Dissection revealed five trematode species in 18 infection combinations. Cercarial emergence failed to reveal many infections and thereby severely underestimated parasitism. Percent failed determinations for each trematode species found were: Himasthla quissetensis (Miller and Northup)= 10.8; Lepocreadium setiferoides (Miller and Northup)= 30.6; Zoogonus rubellus (Olsson)= 43.8; Gynaecotyla adunca (Linton)= 80.2; and Austrobilharzia variglandis (Miller and Northup)= 64.7. Infections in snails harboring two and three trematode species were misrepresented in 80 and 93% of cases, respectively. Overall, cercarial release wrongly determined parasitism in 59.1% of infected snails examined. Thus, as a method, cercarial emergence severely underestimates parasite prevalence and overlooks many species that are present.

THE INFLUENCE OF SEX AND TREMATODE PARASITES ON CARRION RESPONSE OF THE ESTUARINE SNAIL ILYANASSA OBSOLETA.

The estuarine neogastropod, Ilyanassa obsoleta, was studied to determine the influence of sex and trematode parasites on the well-known tendency of this snail to aggregate on carrion. Fifteen experimental arenas (1 x 5 m) were delimited on the Cape Henlopen sandflat in Delaware Bay between July 1982 and November 1983. Snails (n = 2111) were examined by dissection. Frequencies of snails in specific categories of sex and parasitism in the arenas were determined before carrion was made available (expected frequencies), and these frequencies were compared with frequencies of the same categories among snails responding to carrion (observed frequencies). Experiments were categorized for analyses into breeding and nonbreeding temporal groups based upon the presence/absence of females with egg cases. Sexual condition alone affected carrion response. Uninfected females in reproductive condition tended to respond more frequently than predicted by controls (positive response) both during and after reproductive season, or else responded as predicted (neutral response). During breeding season males tended to show a neutral response and afterward to respond less frequently than expected (negative response). Parasite influence on carrion response was not detected until after the breeding season, at which time it was pronounced. Both sexes showed a positive response when infected with Lepocreadium setiferoides. Zoogonus rubellus and Gynaecotyla adunca infections produced negative responses in females but neutral responses in males. Austrobilharzia variglandis was inhibitory to females and probably to males as well. Himasthla quissetensis infections seemed not to affect response of either sex. Multiple infections were relatively frequent (9% of snails examined) and also influenced carrion response.

Cultivation of the cercaria of Himasthla quissetensis (Trematoda) on the chick chorioallantois

Cercariae of Himasthla quissetensis were cultivated on the chick chorioallantois maintained at 38 ± 1°C and a relative humidity of 70–75%. Of 68, 6-day-old eggs, each inoculated with 100 cercariae, 28 (41%) were examined 1–9 days post-inoculation. Of the 28 eggs, 23 (82%) were infected with a total of 224 live worms plus 10 encysted metacercariae. Worms contained blood or hematin-like material in their intestinal caeca and showed considerable development of reproductive structures. A total of 58, 6- or 7-day-old chorioallantoic-worms were serially transferred to new 6-day-old embryos, but only a single live worm was recovered after 13 days on two membranes. Based on fixed and stained specimens, 7-day-old chorioallantoic-worms increased their body area about 4× compared to cercariae and the 13-day-old worm increased its body area about 10×.

Studies on parasitic castration: Soft tissue and shell weights of Ilyanassa obsoleta (Mollusca) parasitized by larval trematodes

The shell lengths, dried shell weights, soft tissue wet weights, and soft tissue dry weights were ascertained for noninfected Ilyanassa obsoleta and for the same snail species naturally infected with the following digeneans: Himasthla quissetensis, Zoogonus lasius, Cercaria dipterocerca, Lepocreadium setiferoides, Microphalloides nassicola, Stephanostomum tenue, and Microbilharzia variglandis. Analyses of the data obtained indicate that infection with all of the trematodes listed above causes neither enhanced growth of soft tissues nor accelerated lengthening of the shell. However, snails infected with sporocysts of Z. lasius have significantly heavier shells than do noninfected snails. These data suggest that infection with Z. lasius may have caused enhanced growth in the form of increased calcium deposition in the shell of I. obsoleta, possibly as a result of parasitic castration. In addition, the mean dry weight of the soft tissues of snails infected with M. variglandis, when normalized for shell length, is significantly lower than that of noninfected snails, possibly as a result of parasite-induced pathology. Finally, comparisons among infected snails indicate a trend toward increased soft tissue dry weight in snails infected with L. setiferoides, although the mean dry weight of these snails does not differ significantly from the mean dry weight of noninfected snails.

Studies on parasitic castration: Aminopeptidase activity levels and protein concentrations in Ilyanassa obsoleta (mollusca) parasitized by larval trematodes

Specimens of the estuarine prosobranch Ilyanassa obsoleta collected in the vicinity of Charleston, South Carolina, during June, July, and August 1981, were found to be parasitized by larvae of the digeneans Cercaria dipterocerca, Himasthla quissetensis, Lepocreadium setiferoides, Microbilharzia variglandis, Microphalloides nassicola, Stephanostomum tenue, and Zoogonus lasius. The aminopeptidase activity levels and the total protein concentrations of the hemocytes and sera of these infected snails were determined. It was ascertained that snails parasitized by larvae of L. setiferoides had significantly higher levels of hemocytic aminopeptidase activity and hemocytic total protein concentrations than noninfected snails. Furthermore, snails parasitized by L. setiferoides larvae had significantly higher hemocytic levels of aminopeptidase activity than snails parasitized by larvae of S. tenue, Z. lasius, M. nassicola, and H. quissetensis.

Excystment of Himasthla quissetensis (Trematoda: Echinostomatidae) Metacercariae In vitro

In vitro experiments with Himasthla quissetensis revealed that excystment involves enzy- matic weakening of the cyst wall and vigorous muscular movements of an activated metacercaria. Maxi- mum excystment occurred following 1) low pH pretreatment, 2) sodium dithionite pretreatment, and 3) a complete excystment medium containing both trypsin and bile salts. Excystment occurred to a lesser degree in the complete medium when all pretreatment was excluded and also in some instances when only partial pretreatment was given. Trypsin alone, with or without pretreatment, caused excystment, but the effect of bile salts alone under the same conditions was minimal. Excystment has been reported or studied for several echinostomes. Howell (1970) stud- ied Echinoparyphium serratum. Danley (1973) described an effective method for ex- cysting Parorchis acanthus, and Fried and Roth (1974) studied aspects of in vitro excyst- ment for the same species. Fried and Grigo (1975) and Fried and Butler (1978) reported on the excystment of Echinoparyphium flex- um, and Echinostoma revolutum, respective- ly. The present study reports on conditions found effective for the in vitro excystment of Himasthla quissetensis metacercariae and in- cludes observations on the behavior of ex- cysting worms.

Growth, Development, and Site Location of the Trematode Himasthla Quissetensis in the Chick Following Cloacal Drop Infections with Cercariae

Infections with Himasthla quissentensis were obtained per cloaca in the domestic chick using cercariae. Worms showed a preference for the ileum where they grew and developed to maturity at a rate comparable to those raised in the gull (Stunkard, 1938). Those from the bursa of Fabricius showed relatively little growth and exhibited gonadal atrophy in some instances.

Himasthla quissetensis and Lepocreadium setiferoides: Emergence patterns from their molluscan host, Nassarius obsoletus

The timing of cercarial release from the intermediate host Nassarius obsoletus, was determined for two species of larval trematodes, Himasthla quissetensis and Lepocreadium setiferoides. In a light-dark schedule the cercariae of H. quissetensis emerged in the first few hours of darkness, while emergence of L. setiferoides was predominantly diurnal. Evidence from both species suggests endogenous control of release under constant conditions. Larvae of L. setiferoides, which possess pigmented eyespots, were photonegative in a light gradient; H. quissetensis larvae, which lack eyespots, showed no phototactic response.