On the Procercoid Protonephridial Systems of Three Diphyllobothrium Species (Cestoda, Pseudophyllidea) and Janicki's Cercomer Theory

Because the types of hooks are so similar in the oncosphacra/procercoid ef cestodes and in several groups of monogenclic trcmatodes and because the exterior of a procercoid with the hooks in a cercomer is so suggestive of a monogenetic nematode, the development of the procercoids of three Diphyllobothrium species was studied. The intention was to determine whether or not the procercoid protonephridial system would have a developmental stage when its type is similar to, or identical with that type which characterizes the monogeneans. Such a conformity would greatly support the theory of a common origin of monogeneans and ceslodes. However, it has emerged that no similar developmental stage exists. The ontogeny revealed a thorough metamorphosis from a very simple primary protonephridial system (identical with that of the miracidium larva in digeneans) to a secondary system, which develops into the system of the adult tapeworm. This fact may be interpreted as an argument against the supposed inter-relalionships between monogeneans and cestodes. However, the type of hooks and the procercoid cercomer still indicate common ancestors. An analysis of the miracidium, the oncosphaera and the oncomiracidium (the monogenean larva) with reference to their different developmental stages when hatching, gave rise to my interpretation of the fundamental structure of both the miracidium and the oncosphaera as primitively simple and not reduced, Especially the identical type of protonephridial system indicates. in my view, that digeneans and ceslodes originally had a common larva type. If the ceslodes and the monogeneans have common ancestors, then the procercoid may be interpreted as the ontogenetic recapitulation of a common hook-armed ancestor, here named hexucanthoid. This rhabdocoelan creature with six hooks in the cercomer and adapted to an ectocommensalic/ectoparasitic mode of life, is thought to have given rise to the monogeneans, the gyrocotylideans, the amphilinideans and the cestodes. The monogeneans were found to have two fundamentally different types of marginal hooks, and on this basis ihe existence of two different lines of evolution in Monogenea is indicated.     

On the Early Development of the Protonephridial Systems in Some Species Belonging to the Genera Diphyllobothrium, Triaenophorus and Schistocephalus (Cestoda, Pseudophyllidea)

Malmberg, G. {Department of Zoology, University of Stockholm, Stockholm, Sweden.) On the early development of the protonephridial systems in some species belonging to the genera Diphyllobothrium, Triaenophorus and Schistocephalus {Cestoda, Pseudophyllidea). Zool. Scripta 1 (5): 227–228, 1972.–The protonephridial systems of coracidia (oncospheres) and procercoids of four Diphyllobothrium species, of Triaenophorus nodulosus (Pallas) and of Schistocephalus solidus (Muller) were studied. In the oncospheres of Diphyllobothrium and Schistocephalus the two flame bulbs of the primary protonephridial system were present, but not in the oncospheres of Triaenophorus. In Schistocephalus the two flame bulbs were found to be inactive in the oncosphere (studied inside the coracidium), but very active in the youngest procercoids, which may imply that the primary protonephridial system does not start its function until the oncosphere has entered the copepod body cavity. The primary protonephridial system of the Triaenophorus procercoids was totally (most specimens) or partly reduced. The secondary protonephridial system, however, began developing more or less simultaneously with the integumental hooklets, the cercomer and the first calcareous bodies, which is in accordance with what is described concerning Diphyllobothrium. The ciliated, excretory bladder described by Rosen in 1919 was found to be a posteriorly open invagination, surrounding the “cercomer shaft”. Reverse bends of the posterior main canals of the secondary system are located closely around the wall of, though very likely not emptying into this invagination.     

鱊头槽绦虫原尾蚴皮层的超微结构观察

利用透射电镜观察了头槽绦虫 (Bothriocephalusacheilognathi)原尾蚴皮层的超微结构。头槽绦虫原尾蚴的皮层为典型的合胞体结构。皮层表面有浓密的微毛与少量的突起。与成虫相比 ,原尾蚴的微毛长而且粗 ,呈现单态性 ,推测在进入终末宿主的过程中有脱落和再生现象。突起分布在头部与体侧 ,含有较少的电子致密颗粒。在原尾蚴皮层细胞质中观察到三种腺细胞的分泌过程 ,即顶分泌、外分泌和微分泌过程。原尾蚴身体后部观察到尾钩和穿刺腺管道的开口。在核周区和纤维层下可见发育较好的环肌与纵肌。本文还对原尾蚴皮层突起的功能进行了探讨。     

Schistocephalus solidus: establishment of tapeworms in sticklebacks--fast food or fast lane?

The penetration of the intestinal mucosal wall is supposed to be critical for helminth parasite infestation, but has rarely been analyzed in detail. We here studied the establishment process of Schistocephalus solidus tapeworms in their second intermediate host, the three-spined stickleback, from oral uptake after experimental exposure, to passage through the gastro-intestinal tract and arrival in the fish body cavity. Using histological techniques, we found tapeworms to penetrate the intestine within 14-24 h, spending most of the time in the stomach lumen and only a very short period in the intestine. Unexpectedly, tapeworms lost their outer layer, together with the cercomer, in the intestine lumen rather than later during intestine wall penetration. Once exposed, the underlying tegument with microtriches might serve to facilitate migration of the parasite into the body cavity.     

Changes in the monocercus cercomer in the cysticercoid cavity and the hemocoel of the nonspecific host

In order to elucidate the functional role of cercomer in larvae of the monocercus type their transplantation from the specific host Chironomus obtusidens to Gammarus lacustris was conducted. At early stages after the transplantation proceeds an increase in the functional activity of the tegument of follicles of the cercomer followed by their complete destruction in 3 or 4 days. On the surface of the exocyst membrane an adhesion of the host's haemocytes occurs, which becomes more distinct in 3-4 days when the process acquires a character of local encapsulation. Within the same period, in the places of haemocytes aggregation, a local resorption of the exocyst external membrane takes place. Later intensification of the host response to transplant is associated with the destruction of follicles of the cercomer. In one case the occurrence of follicles of the cercomer in the cavity of cysticercoid was observed that is caused by the microbe affection of the latter. In the zone of contact of the tegument of scolex and neck with follicles of the cercomer an increased secretion (the microapocrine type) of the tegument, disturbance of the microvillous tegument of the cercomer's follicles and their destruction are observed. Incompatibility of the tegument of definitive departments and cercomer, which arises during differentiation of larvae, is supposed to affect the formation of scolex invagination in the evolution of larvae of Hymenolepis.     

Electron microscopy of the separated outer tegument of the sparganum and its antigenicity

The author reported previously on separation of the outer tegument of the spargana (plerocercoids of Spirometra mansoni) using high concentration of urea solution. To determine which layer of the tegument is separated by this method, an electron microscopic analysis has been processed in this study. It was confirmed that the basement layer of the tegument is separated from the parenchyme of the sparganum. In addition, the antigenicity of the separated outer tegument against the human sparganosis patient sera was evaluated. Numerous antigenic proteins, including 16 and 55 kDa proteins, were noticed in the separated tegument; however, there were no diagnostic 31/36 kDa molecules in this tegument. The molecules reactive with the patient sera in the tegument are to be characterized in future studies.     

Factors affecting abundance of Triaenophorus infection in Cyclops strenuus, and parasite-induced changes in host fitness

Factors affecting the abundance of Triaenophorus crassus and Triaenophorus nodulosus procercoids in their copepod first intermediate host, Cyclops strenuus, and effects of infection on feeding behaviour, reproduction and survival of the host were studied experimentally. When exposed to the same number of coracidia, copepods harboured considerably less procercoids in the trials where ciliates or Artemia salina nauplii were given as alternative food items. The prevalence of infection was higher in adult copepods as compared with copepodite stage IV and stage V, and higher in stage V than in stage IV. The prevalences in adult females and males did not differ significantly from each other. The frequency of females carrying egg sacs was lower among infected than among exposed uninfected and unexposed copepods. The rate of feeding on Artemia nauplii remained at the same level in uninfected copepods, but decreased strongly in infected copepods during 7 days p.i. The survival of unexposed, exposed uninfected and infected copepods did not differ significantly from each other for the first 11 days post-exposure, but the mortality of infected copepods increased significantly after 3 weeks post-exposure. However, the rate of development and mortality of copepods might have been affected by the apparently arrested development of stage IV copepodites found in the experiment. Some of the contradictions between these results and earlier observations are suggested to be caused by the differences in the duration of exposure, intensity of infection and duration of observation post-exposure in the present study as compared with other experiments.     

Production of Polyclonal Antibodies against the Tegument of Sparganum (Plerocercoid of Spirometra mansoni) and Its Immunolocalization

In a previous study, the author developed a method for separation of the tegument of spargana (plerocercoids of Spirometra mansoni) from the parenchyme using urea. The present study, as a next step, was performed to evaluate which molecules are present in the outer tegument. Two major proteins, 180 and 200 kDa, are present in the tegument and we could make polyclonal antibodies against these molecules. Their immunolocalization was processed and the outermost layer of the spargana showed strong positive staining. Conclusively, we could confirm that the 180 and 200 kDa molecules might be tightly bound membrane proteins in the tegument of spargana.     

Differences in adult egg output of Schistocephalus solidus from singly- and multiply-infected sticklebacks

In this study, we recovered Schistocephalus solidus plerocercoids from singly and multiply infected three-spine sticklebacks, Gasterosteus aculeatus, transferred them individually to in vitro culture conditions, and quantified their lifetime egg output. We found a significant difference in the relationships between plerocercoid mass and lifetime egg output for parasites recovered from singly and multiply infected sticklebacks. Although egg output was strongly and positively related to plerocercoid mass amongst worms from singly infected fish, for those recovered from multiply infected sticklebacks the relationship was marginally nonsignificant and negative, with small worms achieving high levels of egg production. We suggest 2 hypotheses that may explain differences in the egg production of plerocercoids from singly and multiply infected fish. One possibility is that smaller plerocercoids in asymmetric multiple infections develop precocially, in response to host manipulation strategies of larger worms that decrease survival prospects of the host. Alternatively, small worms in singly infected sticklebacks may be prevented from becoming sexually mature because they face energetic constraints associated with having to overcome the host's immune response alone. We discuss our results in terms of recent studies examining strategic egg production in helminths.     

Fluorescent vital labeling to track cestodes in a copepod intermediate host

In experimental studies of host-parasite interactions, it is often important to track parasites in their hosts and to discriminate between individual parasites. We used the fluorescent tracer dyes 7-amino-4-chloromethylcoumarin (CMAC) and, 5-chloromethylfluorescein diacetate (CMFDA) for vital labeling of Schistocephalus solidus (Cestoda) coracidia larvae. Labeling was fast and easy to perform and enabled microscopic detection of parasites appearing as procercoids in the hemocoel of the copepod intermediate host at 3 h after exposure. The label was still visible after 14 days. Extensive controls showed that CMAC (20 microM) labeling did not harm tapeworms or copepods. CMFDA (2 microM) reduced host survival, but the dye concentration can be decreased to avoid this in future studies. The new labeling method presented here has been very useful to track S. solidus parasites. It can be valuable for other parasites also and may be particularly suitable for visualization of individual live macroparasites in invertebrate hosts, for which we are not aware of any other appropriate method.     

Effect of Triaenophorus crassus (Cestoda) infection on behavior and susceptibility to predation of the first intermediate host Cyclops strenuus (Copepoda)

Some parasites have been shown to manipulate host behavior so that parasite transmission to the next host is enhanced. Infection with Triaenophorus crassus Forel (Cestoda) caused alterations in the activity and microhabitat selection of the first intermediate host Cyclops strenuus Fischer (Copepoda) in the laboratory. Infected copepods made more starts to swim but spent less time swimming than uninfected copepods. These changes were independent of the intensity of infection. In a water column illuminated from above, infected copepods approached the surface, whereas uninfected ones remained close to the bottom. In the dark both infected and uninfected copepods stayed near the bottom. Finally, infection with T. crassus increased the probability of C. strenuus being eaten by the second intermediate host, whitefish (Coregonus lavaretus L. s.l.), in the laboratory. In experimental infections, 10-day-old procercoids had significantly lower infectivity for whitefish than older (12-, 14-, and 21-day-old) procercoids. Behavioral changes were detected in infected copepods containing procercoids 12 days old or older but not in experiments with 10-day-old procercoids. These results may indicate that T. crassus changes the behavior of the copepod host only after it has become infective to the next host, which is consistent with the active manipulation hypothesis.     

A scanning electron microscope study of the life cycle of Bothriocephalus acheilognathi Yamaguti, 1934

The stages in the life cycle of Bothriocephalus acheilognathi have been studied with the aid of scanning electron microscopy. Emergence of the coracidium occurred after 3–5 days at 20°C. Soon after hatching the coracidium began to swell and the cilia became coiled and lost their locomotory function. The surface of the coracidium was covered in protuberances of unknown function. After consumption by the copepod intermediate host, the coracidium developed into a procercoid. Upon development of a cercomer the procercoid could infect the fish definitive host. Identification of adult B. acheilognathi should be made on specimens relaxed in cold water for 10 min, and be based on the heart shaped scolex and prominent square apical disc.     

Studies on the development of the oncosphere and procercoid of Cyathocephalus truncatus (Cestoda) in the intermediate host, Gammarus pulex

Cultured eggs of Cyathocephalus truncatus were found to develop optimally at 20°C, but they did not develop at 6°C and above. The oncosphere of the tapeworm has been seen to be a true hexacanth embryo. Specimens of the intermediate host. Gammaurs pulex , were infected by being forced to feed on pieces of lettuce leaves on which infective eggs of the tapeworm were placed. The young drveloping porocercoid was first recovered from the haemocoel of Gammarus pulex 5 days after infection. The procercoid was found to reach the infective stage within the amphipod after about ten weeks.     

Early morphogenesis in the platyhelminthes with special reference to egg development and development of cestode larvae

Early development of fertilized eggs is reviewed for the main groups within the phylum Platyhelminthes (Turbellaria, Temnocephaloidea, Monogenea, Digenea, Cestodaria and Cestoda). The Turbellaria show two different patterns of embryological development consequent on whether yolk material is contained within the ovum membrane (endolecithal) or whether yolk is added to the outside of the ovum (ectolecithal). In the parasitic groups, those that are oviparous or ovoviviparous produce shelled eggs of the ectolecithal type and, in addition, there are viviparous forms in which egg development shows variations and the amount of yolk, where present, is reduced. In every case examined, however, cleavage is of the spiral type. Within the Cestoda, clear distinction is made between those groups (orders) of worms which are oviparous as compared to those which are viviparous. It is suggested that oviparity is more primitive (ancestral) than viviparity based on adult morphology and on the evidence of life-cycle studies.The continued, post-oncospheral development of cestodes is described as is the ultrastructure of various representative cercoid larval forms. These include: the procercoid of Pseudophyllidea and Haplobothrioidea; the cercoid of Tetraphyllidea; and, within the Cyclophyllidea, the cercoscolex of the Dilepididae, the cysticercoid of the Hymenolepidae, and the cysticercus of the Taeniidae. During post-oncospheral development, in every case examined the posterior part of the developing larva, the cercomer, can be characterized by a microvillar tegument (at least during early development) whereas the more anterior larval body itself, destined to develop in the definitive host, develops microtriches. Modifications to the cercomer, and its microvilli, in the later stages of post-oncospheral development, occur particularly in the more advanced Cyclophyllidea such as the Taeniidae and in some Hymenolepididae.     

A review of the use of copepods in marine fish larviculture

In spite of the growing interest and success obtained using cultured-copepods, their use in marine aquaculture remains sporadic. Besides, mass culture of several marine copepods has been well established by several authors. However, the upscale of copepod cultures to commercial levels is still a challenge. The practice of using wild copepods from natural ponds which thus increases the risk of parasitic infections of most species has limited their application in aquaculture. The present paper thus emphasizes on recent research efforts focused on the use of chemical treatments and freeze-thawing methods to eradicate procercoids from copepods. Research efforts focused on copepod culture systems which subsequently improved and refined their culture in marine fish larviculture are also well discussed. Advances in the use of copepod eggs as potential source of nauplii for marine fish larvae with special emphasis on the viability, storage conditions and biochemical compositions of the copepod eggs are underscored. Additionally, recent advances in the biochemical compositions (protein, amino acids, pigments, and vitamins) of copepods, which has received relatively little attention compared to researches on the lipid and fatty acid compositions are well emphasized. Specific recommended areas for further research are also proffered.     

Infectivity of plerocercoids of Schistocephalus solidus (Cestoda: Ligulidae) and fecundity of the adults in an experimental definitive host, Gallus gallus.

Aspects of the infectivity of the plerocercoid stage and the fecundity of the adult stage of Schistocephalus solidus were examined using the chicken, Gallus gallus, as an experimental host. To investigate size-related infectivity of the plerocercoid stage to a definitive host, a range of plerocercoids (166) were weighed, and each was fed to an individual male chicken. Only a very small percentage of plerocercoids weighing less than 50 mg established compared with in excess of 50% in all other weight classes. To examine the factors affecting the quantity of eggs produced by the adult stage, 15 similar-sized plerocercoids (160-218 mg) were fed to chickens. The majority of plerocercoids administered established as adults and survived until the experiment was terminated on day 7 postinfection (PI). Fecal egg counts indicated that all established worms commenced egg production on day 2 PI with peak output on day 2 or 3 PI. By day 7 PI, egg production in the surviving worms had declined, but it was still evident. The final weight of the adult and the average egg output per worm were unrelated to the initial weight of the infecting plerocercoid. However, the average egg output was predicted by the final adult dry weight and to a lesser extent by the proportion of weight lost in the transition from plerocercoid to adult, but not by the absolute weight loss.     

A novel phosphagen phosphotransferase in the plerocercoids of Schistocephalus solidus (Cestoda: Pseudophyllidea)

Neither phosphagens nor phosphagen phosphotransferase activity could be detected in Fasciola hepatica, Hymenolepis diminuta, Moniezia expansa or in the plerocercoids of Ligula intestinalis. The plerocercoids of Schistocephalus solidus, however, possess an active taurocyamine phosphotransferase, although it too contains no detectable phosphagens. The taurocyamine phosphotransferase of S. solidus has an absolute requirement for a divalent metal ion and ATP could not be replaced by ITP, GTP, CTP or UTP as the phosphate donor. The role of phosphagens in helminths is discussed.     

Occurrence of Schistocephalus solidus in anadromous threespine stickleback

Plerocercoids of the cestode Schistocephalus solidus are reported for the first time from the body cavity of anadromous threespine stickleback inhabiting Mud Lake, Alaska. Most infected stickleback harbored a single large plerocerciod (mean weight = 0.447 g, range = 0.228-0.716 g). The overall prevalence of plerocercoids across genders and 2 yr of samples was 1.4%, but prevalence was significantly greater in males than in females. Because of the large size of the plerocercoids, anadromous stickleback were probably infected as juveniles before leaving the lake, suggesting that plerocercoids can live in the body cavity of oceanic stickleback for several years.     

Cellular organization of the oncosphere of Mosgovoyia ctenoides (Cestoda: Anoplocephalidae)

The ultrastructure of the infective oncosphere of the cestode Mosgovoyia ctenoides (Anoplocephalidae) is described. The surface of the infective oncosphere is covered by a thin cytoplasmic layer of tegument connected by a narrow cytoplasmic process with the binucleate subtegumental cell, situated deeper in the body. Below the basal matrix of the cytoplasmic layer of the tegument are situated wide bands of the peripheral, somatic musculature responsible for body movements. The 3 pairs of hooks and their muscles form a complex hook muscle system, responsible for coordinated hook action. Five major types of cells have been distinguished: (1) a binucleate subtegumental cell, (2) a binucleate penetration gland, (3) 2 nerve cells, (4) numerous somatic cells, and (5) about 6 germinative cells. The approximate number of cells is 24 (26 nuclei, including 2 syncytial structures). The results of this study, when compared with other published reports from other cestode taxa, support previous hypotheses that the progressive reduction of oncosphere cells is an adaptive feature in cestode evolution.     

Development of the plerocercoid I of Ophiotaenia europaea in reptiles

The existence of a two-host life-cycle in ophiotaeniid proteocephalideans was tested experimentally using Ophiotaenia europaea as a model. Three species of reptiles, Natrix natrix, Natrix tessellata and Lacerta viridis, were fed with experimentally infected copepods containing a large number of infective plerocercoids I. A few plerocercoids, most of which were dead, corresponding morphologically to the plerocercoid II developmental stage of O. europaea, were found encysted in the intestinal wall of N. natrix (8 days p.i.), N. tessellata (5 and 150 days p.i.) and L. viridis (40 days p.i.), while no plerocercoids or adult worms were recovered from their intestines. The results indicate that the infective plerocercoid I of O. europaea cannot undergo further development when ingested directly by the final host (a reptile), and that environmental temperature stimuli cannot initiate a reverse plerocercoid migration to the gut followed by strobilization.