Cystacanth Stage Research Articles

Multidimensionality of Modification in an Isopod-Acanthocephalan System

The acanthocephalan parasite Acanthocephalus dirus infects the freshwater isopod Caecidotea intermedius as an intermediate host before completing its life cycle in a fish. Transmission to the definitive host occurs after the parasite has reached the cystacanth stage and development into this stage is associated with changes in several behavioral and physiological traits of the host. Despite the numerous examples of trait modification in this system, little is known about the multidimensional nature of this modification. Here, we examined the relationships between cystacanth infection and expression of multiple traits (body color, refuge use, activity, and body size) of both male and female C. intermedius. The pattern of multidimensional modification was determined for males and females and then measures of behavioral plasticity, individual consistency and trait correlations were obtained for the modified traits. The results revealed that the overall pattern of host modification differed between males and females. Infected males and females showed similar decreases in body color but differed in changes to the other traits. Infected females were larger and less active than uninfected females, whereas infected males spent less time in refuge than uninfected males. A comparison between two situations revealed that refuge use exhibited high levels of plasticity and activity exhibited high levels of consistency and that these patterns differed based on both host sex and infection status. Analysis of the relationships among modified traits showed that traits appeared to be modified independently of each other and that correlations between traits that existed in one situation were absent in another. We suggest that the pattern of multidimensional modification is sex-specific and that the traits are modified independently. We also show that the patterns of multidimensional modification were not associated with variation in either parasite intensity of parasite size indicting that competitive interactions among parasites did not appear to act as a constraint on host modification.

Stage-dependent behavioural changes but early castration induced by the acanthocephalan parasite Polymorphus minutus in its Gammarus pulex intermediate host.

Multidimensionality in parasite-induced phenotypic alterations (PIPA) has been observed in a large number of host-parasite associations, particularly in parasites with complex life cycles. However, it is still unclear whether such a syndrome is due to the successive activation of independent PIPAs, or results from the synchronous disruption of a single mechanism. The aim of the present study was to investigate the onset and progression of two PIPAs (a behavioural alteration: reversion of geotaxis, and castration) occurring in the crustacean amphipod Gammarus pulex infected with the acanthocephalan Polymorphus minutus, at different parasite developmental stages. Modifications of geotaxis in hosts differed according to the parasite developmental stage. Whereas the cystacanth stage induced a negative geotaxis (exposing the gammarid to predation by birds, the definitive hosts), the acanthella stage, not yet infective for the definitive host, induced a stronger positive geotaxis (presumably protecting gammarids from bird predation). In contrast, castration was almost total at the acanthella stage, with no significant variation in the intensity according to parasite maturation. Finally, no significant correlation was found between the intensity of behavioural changes and the intensity of castration. We discuss our results in relation with current views on the evolution of multidimensionality in PIPA.

Acanthocephalan-related variation in the pattern of energy storage of a behaviorally and physiologically modified host: field data.

The acanthocephalan parasite Acanthocephalus dirus infects the freshwater isopod Caecidotea intermedius as an intermediate host before completing its life cycle in a fish. Transmission to the definitive host occurs after the parasite has reached the cystacanth stage, and development into this stage is associated with changes in several behavioral and physiological traits of the host. Given the potential importance of host energy availability to trait modification, we examined the relationship between cystacanth-stage infection and energy storage of adult isopods. Six samples of infected and uninfected male C. intermedius were collected from a population in March, April, and May during which time cystacanth-stage A. dirus dominate infections and modification of behavior and physiology occurs in nature. Biochemical assays revealed that infected male C. intermedius contained more glycogen and more lipid than uninfected males and that this difference was present throughout the sampling period, which represents the entire adult phase of the host's life. Additional analysis revealed that infected and uninfected males differed in their pattern of allocation to each energy source and that host lipid levels were negatively correlated with parasite intensity. We propose that the typical pattern of allocation and storage of host energy appears to be disrupted by A. dirus infection and that the changes are more likely to favor the parasite than the host.

The life cycle ofSclerocollum saudiiAl-Jahdali, 2010 (Acanthocephala: Palaeacanthocephala: Rhadinorhynchidae) in amphipod and fish hosts from the Red Sea

The rhadinorhynchid Sclerocollum saudii Al-Jahdali, 2010 was found in the intestine of its type host, Siganus rivulatus Forsskål & Niebuhr, 1775, a siganid fish permanently resident in a lagoon within the mangrove swamps found on the Egyptian coast of the Gulf of Aqaba (between 28°7'N and 28°18'N). Larval forms of this acanthocephalan (acanthors, acanthellae and cystacanths) were only found in Megaluropus agilis Hoek, 1889 (Crustacea: Gammaridae), a benthic amphipod abundant on algae and seagrasses in the lagoon. So, this life cycle of S. saudii was elucidated under semi-natural conditions: embryonated eggs of S. saudii were directly ingested by the amphipod and hatched in its intestine; the released acanthor penetrated the intestinal epithelium in 12-18 h to reach the connective tissue serosa, where it remained for about 3 days, then penetrated the intestinal wall and remained attached to its outer surface for 4 days. It then detached and dropped free in the amphipod haemocoel and transformed into an oval acanthella, growing for 16 days to reach the cystacanth stage. The cystacanth at 46 days post-infection was infective to fish (excysted in its intestine as an active juvenile). Male and female juveniles reached maturity 17 and 23 days post-infection. Recently copulated females first appeared 26 days post-infection and all females seemed to be copulated at 28 days post-infection; partially and fully gravid females first appeared 31 and 35 days post-infection. Mature males and fully gravid females started to die off naturally 31 and 43 days post-infection and were totally expelled from the fish intestine by 42 and 52 days post-infection. The cycle was completed in 89 days and is similar to other known palaeacanthocephalan life cycles, but has its own characteristics.

Helminth Parasites of the Three Racerunner Lizards: Eremias pleskei Nikolsky, 1905 (Pleske’s Racerunner-Transcaucasian Racerunner), Eremias strauchi Kessler, 1878 (Strauch’s Racerunner) and Eremias suphani Basoglu & Hellmich, 1968 (Suphan Racerunner) collected from Eastern Part of Turkey

Abstract In this investigation, a total of 44 racerunner lizard samples (Eremias pleskei, Eremias strauchi, and Eremias suphani) collected from eastern part of Turkey were examined for the first time for helminths. Eremias pleskei was harboured 1 species of acanthocepalan (in cystacanth stage), E. strauchi was harboured 2 species of nematodes, and E. suphani was harboured 3 species of nematodes and 1 species of cestode. E. strauchi represents a new host record for Spauligodon eremiasi, and Spauligodon saxicolae E. suphani represents a new host record for Spauligodon eremiasi, S. saxicolae, Physaloptera sp., and Oochoristica tuberculata, and also, E. pleskei represents a new host record for unidentified acanthocepalan (in cystacanth stage). Also, Turkey is a new locality record for Spauligodon eremiasi.

Co‐variation between the intensity of behavioural manipulation and parasite development time in an acanthocephalan–amphipod system

Pomphorhynchus laevis, a fish acanthocephalan parasite, manipulates the behaviour of its gammarid intermediate host to increase its trophic transmission to the definitive host. However, the intensity of behavioural manipulation is variable between individual gammarids and between parasite populations. To elucidate causes of this variability, we compared the level of phototaxis alteration induced by different parasite sibships from one population, using experimental infections of Gammarus pulex by P.laevis. We used a naive gammarid population, and we carried out our experiments in two steps, during spring and winter. Moreover, we also investigated co-variation between phototaxis (at different stages of infection, 'young' and 'old cystacanth stage') and two other fitness-related traits, infectivity and development time. Three main parameters could explain the parasite intra-population variation in behavioural manipulation. The genetic variation, suggested by the differences between parasite families, was lower than the variation owing to an (unidentified) environmental factor. Moreover, a correlation was found between development rate and the intensity of behavioural change, the fastest growing parasites being unable to induce rapid phototaxis reversal. This suggests that parasites cannot optimize at the same time these two important parameters of their fitness, and this could explain a part of the variation observed in the wild.

Helminth Fauna of the Nine-Banded Armadillo (Dasypus novemcinctus) in North-Central Florida

The gastrointestinal tracts of 32 free-ranging, 9-banded armadillos (Dasypus novemcinctus) from north-central Florida were examined for the presence of helminths during July 1991 to November 1993. Aspidodera sp. (Nematoda: Aspidoderidae), most closely resembling Aspidodera sogandaresi, were recovered from 20 of 32 armadillos examined. Total numbers of A. sogandaresi ranged from 1 to 1,021 per infected animal, and followed an inverse correlation to body condition index for those animals. The cystacanth stage of 1 acanthocephalan, Macracanthorhynchus ingens, was present in 1 armadillo, and is the first report of M. ingens in the 9-banded armadillo. The present study contributes to the known natural history of the 9-banded armadillo, an important animal research model.

The effects of parasite age and intensity on variability in acanthocephalan-induced behavioural manipulation

Numerous parasites with complex life cycles are able to manipulate the behaviour of their intermediate host in a way that increases their trophic transmission to the definitive host. Pomphorhynchus laevis, an acanthocephalan parasite, is known to reverse the phototactic behaviour of its amphipod intermediate host, Gammarus pulex, leading to an increased predation by fish hosts. However, levels of behavioural manipulation exhibited by naturally-infected gammarids are extremely variable, with some individuals being strongly manipulated whilst others are almost not affected by infection. To investigate parasite age and parasite intensity as potential sources of this variation, we carried out controlled experimental infections on gammarids using parasites from two different populations. We first determined that parasite intensity increased with exposure dose, but found no relationship between infection and host mortality. Repeated measures confirmed that the parasite alters host behaviour only when it reaches the cystacanth stage which is infective for the definitive host. They also revealed, we believe for the first time, that the older the cystacanth, the more it manipulates its host. The age of the parasite is therefore a major source of variation in parasite manipulation. The number of parasites within a host was also a source of variation. Manipulation was higher in hosts infected by two parasites than in singly infected ones, but above this intensity, manipulation did not increase. Since the development time of the parasite was also different according to parasite intensity (it was longer in doubly infected hosts than in singly infected ones, but did not increase more in multi-infected hosts), individual parasite fitness could depend on the compromise between development time and manipulation efficiency. Finally, the two parasite populations tested induced slightly different degrees of behavioural manipulation.

PARASITE-RELATED PAIRING SUCCESS IN AN INTERMEDIATE HOST, CAECIDOTEA INTERMEDIUS (ISOPODA): EFFECTS OF MALE BEHAVIOR AND REPRODUCTIVE PHYSIOLOGY

The acanthocephalan parasite Acanthocephalus dirus develops from the egg to the cystacanth stage inside the freshwater isopod Caecidotea intermedius. We have shown previously that cystacanth-infected male C. intermedius are less likely to initiate mating attempts with females than uninfected males in competitive situations. Here, we used a field-based experiment to examine whether cystacanth-infected males were also less likely to initiate mating attempts with females in noncompetitive situations. We found that infected males were less responsive to females than uninfected males, and we propose that the cystacanth-related change in male mating behavior is mediated by a change in the mating response of males to females rather than male-male competition. We then examined whether cystacanth-related changes in reproductive function, i.e., sperm content and fertilization ability, could explain this variation in male mating behavior. We found that cystacanth-infected males contained both developing and mature sperm and fertilized as many eggs as uninfected males. Thus, we propose that changes in reproductive function are unlikely to explain cystacanth-related variation in male mating behavior in C. intermedius.

Development-related effects of an acanthocephalan parasite on pairing success of its intermediate host

The acanthocephalan parasite, Acanthocephalus dirus , undergoes larval development in the aquatic isopod, Caecidotea intermedius , before completing its life cycle in the intestine of a fish (e.g. sunfish). Inside C. intermedius , the parasite develops through noninfective acanthor and acanthella stages and into the cystacanth stage, which is infective to definitive hosts. Research has shown that individual A. dirus induce phenotypic changes in C. intermedius that increase conspicuousness to definitive hosts, and that the level of modification is most pronounced when the parasite has developed into the cystacanth stage. We examined whether development into the cystacanth stage also correlated with changes in mating behaviour of the host. Using a field survey, we quantified the pattern of development of larval A. dirus to identify specific periods when either infective (cystacanth) or noninfective (acanthor, acanthella) stages dominated. Males infected with cystacanth-stage larvae had lower pairing success than males infected with larvae in the noninfective stages. To identify the behavioural mechanisms underlying this relation (i.e. male response to females, female resistance), we used a field-based experiment to examine the relation between parasite development and mating interactions between males and females. Cystacanth-infected males were less likely to initiate mating attempts with females than were acanthor/acanthella-infected males, and this effect could explain the population-level mating pattern. We discuss the results in the context of both adaptive and nonadaptive mechanisms underlying parasite-mediated changes in mating behaviour.

A comparative analysis of adult body size and its correlates in acanthocephalan parasites

Adult acanthocephalan body sizes vary interspecifically over more than two orders of magnitude; yet, despite its importance for our understanding of the coevolutionary links between hosts and parasites, this variation remains unexplained. Here, we used a comparative analysis to investigate how final adult sizes and relative increments in size following establishment in the definitive host are influenced by three potential determinants of acanthocephalan sizes: initial (cystacanth) size at infection, host body mass, and the thermal regime experienced during growth, i.e. whether the definitive host is an ectotherm or an endotherm. Relative growth from the cystacanth stage to the adult stage ranged from twofold to more than 10,000-fold across acanthocephalan species, averaging just over 100-fold. However, this relative increment in size did not correlate with host mass, and did not differ between acanthocephalan species using ectothermic hosts and those growing in endothermic hosts. In contrast, final acanthocephalan adult sizes correlated positively with host mass, and after correction for host mass, final adult sizes were higher in species parasitising endotherms than in those found in ectotherms. The relationship between host mass and acanthocephalan adult size practically disappears, however, once phylogenetic influences are taken into account. Positive relationships between adult acanthocephalan size, cystacanth size and egg size indicate that a given relative size is a feature of an acanthocephalan species at all stages of its life cycle. These relationships also suggest that adult size is to some extent determined by cystacanth size, and that the characteristics of the definitive host are not the sole determinants of parasite life history traits.

Effects of Coinfection with Pomphorhynchus bulbocolli on Development of Leptorhynchoides thecatus (Acanthocephala) in Amphipods (Hyalella azteca)

The effect of the presence of Pomphorhynchus bulbocolli on the development of Leptorhynchoides thecatus (Acanthocephala) in amphipod intermediate hosts (Hyalella azteca) was examined. Two groups of amphipods were exposed either to eggs of both species (experimental) or only to L. thecatus eggs (control). Amphipods of both groups were dissected 39 days postexposure. The percentage of L. thecatus at the cystacanth stage and mean abundance of cystacanths and precystacanths per amphipod were determined. Contingency table analysis and Fisher's exact tests demonstrated that a significantly smaller proportion of L. thecatus reached the cystacanth stage in coinfected amphipods of the experimental group than either worms in the control group or worms in L. thecatus-only infections of the experimental group. Interspecific interaction between acanthocephalans in intermediate hosts has not been reported previously. Coinfection reduces the number of L. thecatus in amphipods available for transmission to definitive hosts. Habitat separation by eggs of L. thecatus and P. bulbocolli might reduce this effect if amphipods are less likely to become coinfected when eggs are in different microhabitats than when they are not.

Cypria reptans (Crustacea: Ostracoda) as an Intermediate Host of Neoechinorhynchus rutili (Acanthocephala: Eoacanthocephala) in Italy

A total of 2,568 specimens of 3 species of ostracod, namely Herpetocypris sp., Ilyocypris sp., and Cypria reptans Brohnstein, 1928, was collected between November 1994 and April 1995 from the Ceresina Canal, a tributary of the River Brenta (northern Italy), and examined for larval helminths. Larvae of Neoechinorhynchus rutili Müller, 1780 were found in the hemocoel of C. reptans. The prevalence of infection ranged from 8.57 to 14.51%. Most larvae were in the cystacanth stage (a new geographical record for this cystacanth). Not more than 3 larvae were encountered in a single host. Among 48 aquatic alder fly larvae of Sialis lutaria collected over 6 mo, together with the crustacean, no infected larvae were encountered. Specimens of Gasterosteus aculeatus (Pisces: Gasterosteiformis) collected with the arthropods from the same site were found to be parasitized with adult N. rutili. Fish stomach content analysis showed ostracods to be a major food item of three-spined sticklebacks in the study area during much of the year.

Behavioural modifications and increased predation risk of Gammarus pulex infected with Polymorphus minutus

Experiments are described which investigated altered behavioural responses in Gammarus pulex infected with the cystacanth stage of Polymorphus minutus. Infected gammarids were significantly smaller than non-infected individuals, suggesting that growth and development of the host may have been affected by the parasite. Infected gammarids responded to disturbance by movement to the water surface, whereas controls moved along the substratum. Furthermore, infected G. pulex spent significantly more time swimming in surface water compared with non-infected individuals, when undisturbed. This latter behavioural modification was depth-dependent. Susceptibility to predation by fish was significantly enhanced by infection with P. minutus. These results suggest that P. minutus can selectively modify certain aspects of the behavioural repertoire of G. pulex, thus increasing the visual profile of the amphipods, and their likelihood of predation by vertebrate predators including the definitive host.

Ovarian tissue in juvenile palaeacanthocephalans: Corynosoma semerme, C. strumosum and Echinorhynchus gadi

SUMMARYThe structure of the ovarian tissue in juvenile Corynosoma semerme and C. strumosum from a fish paratenic host and in the cystacanth stage of Echinorhynchus gadi from an amphipod intermediate host was investigated by means of transmission electron microscopy. The species were obtained from hosts living in the Baltic Sea. The observations indicate that ovarian development was more advanced in cystacanths of E. gadi than in juveniles of C. semerme and C. strumosum. Free ovaries were present in E. gadi with an obvious supporting syncytium and surface microvilli. The biological significance of the different stages of ovarian development in these species is discussed briefly in relation to either reproductive strategies and host specificity in definitive hosts or to the attainment of infectivity by cystacanths in intermediate hosts.

Life History and Population Biology of Larval Acanthocephalus lucii (Acanthocephala: Echinorhynchidae) in the Isopod Asellus aquaticus

Hemocoels of 8,731 Asellus aquaticus collected from the Forth and Clyde canal in Glasgow, Scotland, from January 1980 to March 1981 were examined for larvae of Acanthocephalus lucii. Prevalence and mean intensity were generally low (1.5-8.3% and 1.0-1.6, respectively), but there was a slight seasonal infection pattern with fewer infected isopods during summer, reflecting the appearance of a new isopod generation. Although there were no distinct seasonal trends in the proportions of each larval stage, recruitment of larvae probably occurred mainly during summer and autumn. Some larvae reached the cystacanth stage by late summer or autumn; others overwintered as acanthors or acanthellae and completed development the following spring. The maximum life span of larvae was limited to 1 yr by annual turnover of the isopod population. The distribution of larval A. lucii among isopods was slightly aggregated. There was a peaked pattern in the relationship between isopod length and the prevalence, abundance, and degree of parasite aggregation. The rate of parasite development in laboratory-infected isopods was linearly related to temperature between 9 and 22 C; the temperature threshold was 5.7 C, and the larval parasite required 598 degree-days above threshold to complete development. Among laboratory-infected isopods, 2 mechanisms that could regulate the larval parasite population were detected: intraspecific competition and direct, parasite-induced isopod mortality. However, the intensity of infection in the natural habitat was consistently low and may have remained below the level at which these mechanisms operated.

Observations on the morphology of the testis in the larvae ofMoniliformis(Acanthocephala)

SUMMARYTestes in the male early acanthella ofMoniliformis dubiusare cellular. The testes in the middle and late acanthellae and cystacanth stage also contain individual cells but these are embedded in a compact supporting syncytium which also forms the boundary of the testis. The testes are embedded in the cytoplasmic wall of the ligament sac in the early acanthella but after this stage they become exposed in the cavity of the sac when the surfaces of the testes become covered by a surface coat. Certain cells adjacent to testes primordia in the early acanthella appeared to have formed rudiments of vasa efferentia in the middle acanthella.

The Life Cycle of Octospiniferoides chandleri Bullock, 1957 (Acanthocephala: Neoechinorhynchidae) with Some Observations on Parasite-Induced, Photophilic Behavior in Ostracods

The ostracods, Cypridopsis vidua (Mueller, 1776) and Physocypria pustulosa (Sharpe, 1898) became infected with Octospiniferoides chandleri after eating shelled acanthors removed from the pseu- docoel of adult, female acanthocephalans. At 23 C, 20 days were required for development to the cystacanth stage and 23-day-old cystacanths were infective to mosquitofish, Gambusia affinis. Developmental stages in the ostracod were similar to those described for other neoechinorhynchid acanthocephalans. In the fish host, approximately 30 days were required for development of the parasite to full sexual maturity. Trans- mission of the parasite to the definitive host was aided by a parasite-induced, positive response to light in ostracod hosts and by transfer of enteric worms through cannibalism in Gambusia. Octospiniferoides chandleri was described by Bullock (1957) on the basis of two imma- ture females collected from gulfkillifish, Fun- dulus grandis, near Gilchrist, Texas. Yama- guti (1963) tentatively assigned 0. chandleri to the genus Octospinifer. Subsequent ex- amination of material from the west coast of Florida (Bullock, 1966) indicated that the ma-

Glycogen Metabolism in Larval Moniliformis dubius (Acanthocephala)

Study of glycogen metabolism in larval Moniliformis dubius showed significant increase in the rate of metabolism as a result of activation of the cystacanths by bile salts. Anaerobiosis with increased levels of C02 also enhanced the rate of metabolism, a possible explanation of apparent enhancement of activation of the cystacanths by this gas phase. From the results of this study it appears that the role of the gas phase can be explained in terms of the nature of metabolic end products formed. The mechanism by which bile salts elicit the increase in rate of glycogen metabolism could not be determined. Graff and Kitzman (1965) reported that bile salts in vitro or bile of the host in vivo activate the cystacanth of Moniliformis dubius. They also noted that anaerobiosis and increased levels of CO2 enhanced the rate of bile salt activation of this larval parasite. In the rat host, rapid growth of the parasite follows activation and establishment of the cystacanth in the gut. Since Read and Rothman (1958) showed that M. dubius requires carbohydrate from the host's diet as a factor for growth and Fisher (unpublished) quoted by Graff and Kitzman (loc. cit.) stated that the cystacanth of M. dubius contains only small amounts of stored carbohydrate, a study was undertaken to determine the exact amount of glycogen present in the cystacanth as it reaches infective stage and to determine some of the parameters of its metabolism following activation. MATERIALS AND METHODS Maintenance of hosts and the life cycle The definitive host, Holtzman white rats (Holtzman Rat Co.), were maintained in groups of 10 to 20 in 12by 15by 18-inch wire mesh cages in air-conditioned quarters. They were provided Laboratory Chow (Ralston Purina Co.) and tap water ad lib. Only male rats were used. Periplaneta americana, the intermediate hosts, were maintained in painted 5to 15-gal aquaria on a diet of fresh apples, powdered rat chow, and water. Received for publication 26 May 1970. * From a dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy. t Supported in part by grants from the USPHS (GM 12263 and 5-T01-AI 00106) and by a predoctoral fellowship to the author (GM 37755). t Present address: Department of Biology, Texas A&M University, College Station, Texas 77843. Eggs of Moniliformis dubius were obtained from gravid female worms and concentrated by sedimentation in tap water. After removal of excess moisture by blotting on filter paper, the eggs were mixed in a ratio approximately 1:1 with fresh minced apple and the mixture was presented to cockroaches which had been denied food and water for the previous week. Complete development to the cystacanth stage in the hemocoel of the cockroaches required approximately 90 days at 24 to 28 C. To complete the life cycle, male rats of 60 to 90 g weight were infected with 25 cystacanths. Adult M. dubius were recovered 40 to 45 days later upon necropsy of the hosts. Handling of the cystacanths Infective cystacanths were removed from the cockroaches by flushing the hemocoel with KrebsRinger saline buffered at pH 7.4 with 0.025 M tris(hydroxymethylamino) methanemaleate, hereafter referred to as KRT. In experiments involving the use of cystacanths, the cyst wall was removed by expressing the intact cystacanths through a narrow tipped pipette which allowed passage of the larvae but impeded the passage of the cysts. The larvae were examined under a dissecting microscope for possible anatomical damage and/or abnormalities and o ly anatomically perfect larvae were selected. The use of a short glass cylinder having a stainless steel mesh bottom facilitated the rapid handling of the cystacanths during experiments and permitted he extraction of larvae by immersion of the cylinders nd the parasites in a given volume of 70% ethanol. Wet and ethanol-extracted dry weight ratios were determined using groups of 50 cystacanths, which were extracted for 18 hr in 70% ethanol and dried at 95 C for 24 hr. All incubations were performed in KRT. The gas phases during incubations were established by equilibrating the media for 5 min with either air, ir-CO2 (95:5), N2 (100), or N2-C02 (95:5). Bicarbonate was added to all CO2-equilibrated preparations in concentrations to maintain pH 7.4 at 37 C following gas phase equilibration.

Aspects of the Development of Moniliformis dubius

Descriptive and experimental studies were made on Moniliformis dubius development. In the intermediate host, Periplaneta americana, two acanthor stages, six acanthella stages, and the cystacanth stage were recognized. In stage I acanthellae much of the central nuclear mass has become cellular; in stage II acanthellae protonephridial primordia were observed. The cystacanth is laterally compressed. Differentiation of the body wall musculature is almost complete after 1 week in the definitive host. Larval development rate was not affected by age of host (i.e., middle or late nymphal instar or adult) or sex of adult host, or by the presence of large numbers of larvae. Different stages of acanthella development may occur within a single roach. Injection of larval stages into the hemocoel of previously uninfected roaches did not impair subsequent development. Preadult worms were established in previously uninfected rats by surgical transfer. Successful transferral of life cycle stages may be useful in further studies of morphogenesis. Moniliformis dubius Meyer, 1933 has become the most commonly used acanthocephalan for experimental investigations. Recently published work on this species includes studies of the metabolism (Bryant and Nicholas, 1965; Edmonds, 1965; Graff, 1965); cystacanth excystment (Graff and Kitzman, 1965); in vitro culture (Nicholas and Grigg, 1965); ultrastructure of the tegument (Nicholas and Mercer, 1965); and chromosomes (Robinson, 1965). The purpose of the present study was to obtain a detailed cytological and morphological picture of normal development patterns in M. dubius as a preliminary to the investigation of the effects of exposure of various life cycle stages to ionizing radiation. A comprehensive account of the development of M. dubius is not given here. Such a description would be redundant in view of the published accounts of the life cycle and development of this species (Yamaguti and Miyata, 1942; Moore, 1946). However, some features of normal development and developmental variation which are not mentioned in earlier accounts are given in this report, together with details of parasite transferral techniques of potential use in experimental studies of larval and adult develop-