Parasitol Res (2012) 110:1009–1017 DOI 10.1007/s00436-011-2590-2
ORIGINAL PAPER
Early intrauterine embryonic development in Khawia sinensis Hsü, 1935 (Cestoda, Caryophyllidea, Lytocestidae), an invasive tapeworm of carp (Cyprinus carpio): an ultrastructural study Magdaléna Bruňanská & John S. Mackiewicz & Daniel Młocicki & Zdzisław Świderski & Jana Nebesářová
Received: 7 June 2011 / Accepted: 1 August 2011 / Published online: 6 September 2011 # Springer-Verlag 2011
Abstract Intrauterine embryonic development in the caryophyllidean tapeworm Khawia sinensis has been investigated using transmission electron microscopy and cytochemical staining with periodic acid-thiosemicarbazide-silver proteinate for glycogen. Contrary to previous light microscopy findings that reported the release of non-embryonated eggs of K. sinenesis to the external environment, the present study documents various stages of embryonation (ovoviviparity) within the intrauterine eggs of this cestode. At the initial stage of embryonic development, each fertilised oocyte is M. Bruňanská (*) Parasitological Institute, Slovak Academy of Sciences, Hlinkova 3, 040 01 Košice, Slovak Republic e-mail:
[email protected] J. S. Mackiewicz Department of Biological Sciences, University at Albany, State University of New York, Albany, NY, USA D. Młocicki : Z. Świderski W. Stefanski Institute of Parasitology, Polish Academy of Sciences, Twarda 51/55, 00-818 Warsaw, Poland D. Młocicki : Z. Świderski Department of General Biology and Parasitology, Medical University of Warsaw, Chałubińskiego 5, 02-004 Warsaw, Poland J. Nebesářová Institute of Parasitology, Biology Centre of the Academy of Sciences of the Czech Republic, Branišovská 31, 37005 České Budějovice, Czech Republic
accompanied by several vitellocytes that become enclosed within the operculate, electrondense shell. Cleavage divisions result in formation of blastomeres (up to about 24 cells) of various sizes. Mitotic divisions and apparent rosette arrangment of the blastomeres, the latter atypical within the Eucestoda, are observed for the first time in the intrauterine eggs of K. sinenesis. The early embryo enclosed within the electrondense shell is surrounded by a thin membraneous layer which in some enlarged regions shows presence of nuclei. Simultaneously to multiplication and differentiation, some of the blastomeres undergo deterioration. A progressive degeneration of the vitellocytes within eggs provides nutritive reserves, including lipids, for the developing embryo. The possible significance of this atypical timing of the intrauterine embryonic development to (1) the ecology of K. sinensis and that of a recent introduction of another invasive tapeworm, the caryophyllidean Atractolytocestus huronensis Anthony, 1958 to Europe; and (2) the affiliation of caryophyllideans with other lower cestodes, are discussed.
Introduction The order Caryophyllidea occupies a key position among the Eucestoda (Mackiewicz 2003). Caryophyllidean tapeworms are characterised by having a monopleuroid body, i.e. lacking proglottisation and with a single set of reproductive organs. While eggs are generally unembryonated when expelled (Mackiewicz 1968, 1972), some exceptions have been reported, e.g. progenetic Archigetes in which embryonation is usually completed in utero, or at least begins in utero and terminates ex utero (Wiśniewski 1930; Kennedy 1965; Calentine 1984), or Djombangia, Wenyonia spp., Hunturella, or Biacetabulum sp. (Mackiewicz 1972). Detailed observa-
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tions on the early intrauterine development are limited to Archigetes appendiculatus, a light microscopy study by Motomura (1929) and Wenyonia virilis, an ultrastructural study by Młocicki et al. (2010b). In the course of recent ultrastructural studies on the male reproductive system of Khawia sinenesis by Bruňanská (2009, 2010), new observations were made on the fine structure of female reproductive organs. Surprisingly, the preliminary findings indicated signs of ongoing embryonic development within intrauterine eggs. On the other hand, earlier reports by Demshin and Dvoryadkin (1980), Protasova et al. (1990) and Scholz (1991) described freshly released eggs of K. sinenesis as being unembryonated, and composed of a zygote and several vitellocytes. Unfortunately, there are no studies of the embryonic development of K. sinensis that describe cell types, cell number or associate structures as envelopes. The aim of the present study is two-fold: (a) to clarify the state of intrauterine egg development in K. sinensis and (b) to relate new observations to the present knowledge on embryonic development in caryophyllidean cestodes and consider the functional significance of intrauterine embryogenesis in K. sinensis.
Materials and methods Specimens of K. sinensis were removed from the intestine of Cyprinus carpio from the fish pond Bošilec (near Třeboň), South Bohemia, Czech Republic in November 2003. Living worms were cooled in 0.9% NaCl solution and then fixed in 2.5% glutaraldehyde in 0.1 M cacodylate buffer, pH 7.2, for 3 h at 4°C. The worms were cut into small pieces, rinsed in the same buffer and post-fixed in 1% OsO4 at 4°C for 2 h, followed by dehydration in graded alcohol series and embedding in Spurr's epoxy resin. A series of ultrathin sections were cut using a Leica Ultracut UCT ultramicrotome, placed on copper grids and doublestained with uranyl acetate and lead citrate. The grids were examined in a JEOL 1010 transmission electron microscope operated at 80 kV. The periodic acid-thiosemicarbazide-silver proteinate technique of Thiéry (1967) was applied in order to determine specific cytochemical localization of glycogen at the ultrastructural level.
Results Intrauterine eggs of K. sinensis are already thick-shelled and operculate (Figs. 1, 2 and 3). The operculate pole is electrondense and often slightly more pitted than the rest of the shell (Fig. 2). A conspicuous constriction with a suture
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indicates the junction separating the operculum from the remaining electrondense shell (Fig. 3). This ultrastructural feature indicates that the operculum is fully formed and able to be opened. A great variety of developmental stages, from 2 to about 24 blastomeres, was observed within the intrauterine eggs. The earliest developmental stage is represented by a fertilised oocyte which is accompanied by several (up to seven) vitellocytes (Figs. 1 and 4). The cytoplasm of the vitellocytes within the egg still contains prominent electrondense aggregations of glycogen, together with shell globules (Figs. 1 and 4). However, rapid degeneration of vitellocytes is in progress, including sporadical occurrence of lipid droplets (Fig. 5). In addition, GER-bodies (=structures originating of granular endoplasmic reticulum) are detected in the cytoplasm of degenerating vitellocytes (Figs. 2; 5 inset). The fertilised oocyte contains a large nucleus with an electrondense very small nucleolus and a few minute heterochromatin islands scattered in the nucleoplasm (Fig. 6). Numerous small mitochondria are present in the oocyte cytoplasm. The zygote stage of the embryonic development is followed by cleavage divisions, giving rise to macromeres, mesomeres and micromeres (Fig. 7). The macromeres are the largest blastomeres with large lobed nuclei and spherical nucleoli. The moderately electrondense nucleoplasm includes numerous small heterochromatin islands. Within the granular cytoplasm of the macromeres are a few mitochondria. Mesomeres and micromeres differ from macromeres by their size and the fine structure of their nuclei (Fig. 7). Medium-sized mesomeres have large nuclei whose nucleoplasm is equipped with more numerous and large islands of condensed heterochromatin, when compared with macromeres. Micromeres are characterised by a spherical, highly condensed nucleus surrounded by a very thin layer of granular cytoplasm. A rosette-like arrangement of the blastomeres (Figs. 8 and 9) was observed occasionaly. The cells of these rosettes are apparently connected to the central cytoplasmic region by narrow cytoplasmic processes. The central cytoplasm is about the same electrondensity as the adjacent blastomeres. At this stage, large osmiophilic dense bodies can be identified in the cytoplasm of degenerating vitellocytes within the egg (Fig. 9). Typical mitotic divisions of the blastomeres are readily apparent in the intrauterine eggs of K. sinensis (Figs. 10, 11, 12, 13 and 14). Dividing cells in pro- and anaphase are situated mostly at the periphery of the early embryos. Dividing blastomeres in later stages of development of the embryo are situated in close vicinity of shell or degenerating vitellocytes (Fig. 11). In addition, the shape of the nucleus of several blastomeres becomes lobed. Blastomere multiplication and differentiation takes place simultaneously with a degeneration of some of them (Figs. 10,
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Fig. 1–5 1 Intrauterine eggs of K. sinensis. Fertilised oocyte (O) and vitellocytes (VC) enclosed in a thick electrondense shell (ES) with an operculum (Op). Note numerous shell globule clusters (SGC) within the cytoplasm of vitellocytes. g glycogen. Bar=10 μm. 2 A detail of the operculate region (Op) of the two intrauterine eggs. Both opercula have a pitted appearance. VC vitellocyte, GB GER body. Bar=5 μm. 3 A conspicuous constriction with a suture (arrow) indicates the junction that separates the operculum (Op) from the remaining
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electrondense shell (ES). VC vitellocyte. Bar=5 μm. 4 Vitellocytes (VC) within intrauterine eggs are rich in glycogen (g). Thiéry method. O fertilised oocyte, N nucleus. Bar=10 μm. 5 Lipid droplets (L) can be found occasionally in the degrading vitellocytes (VC) within the intrauterine eggs. Thiéry method. g glycogen, ES eggshell. Bar=2.5 μm. Inset A detail of GER-bodies (GB) within the cytoplasm of the degrading vitellocytes from intrauterine eggs. Bar=0.65 μm
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Fig. 6–9 6 A fertilised oocyte has a large nucleus (N) with prominent nucleolus (Nu) and a minute heterochromatin islands (Hc). The cytoplasm is rich in mitochondria (M). Bar=2 μm. 7 Early cleavage division results in formation of three types of blastomeres: macromeres (Ma), mesomeres (Me) and micromeres (Mi). Hc heterochromatin, M mitochondrion, N nucleus, Nu nucleolus, VC vitellocyte. Bar=5 μm. 8 A portion of a rosette like arrangement of several blastomeres (B)
linked by cytoplasmic bridges to a central cytoplasm mass (CP). Note the lobed nuclei (N) of some of the blastomeres. DBo dense bodies of degenerating vitellocytes. Bar=5 μm. 9 Rosette arrangement of blastomeres (B) at more advanced stage of embryo development. CP central cytoplasm mass, ES electrondense shell, Op operculum, VC vitelline cell, DBo dense bodies of degenerating vitellocytes. Bar=10 μm
12 and 13). Degenerating blastomeres resembling areas of focal cytoplasmic degeneration increase in number. They are localised either at the periphery or in the centre of the embryo. Lobed nuclei of degenerating blastomeres increase in number (Fig. 12). The lobed nuclei and degeneration of blastomeres may be directly associated with each other (Fig. 13). The remnants of degenerating vitellocytes have never been observed to fuse with the cytoplasm of blastomeres. The late cleavage embryo is surrounded by a
thin membraneous layer, which may contain flattened nuclei (Figs. 12 and 14).
Discussion Results of the present study provide direct evidence for the first time that embryonic development of K. sinensis already starts in utero. Contrary to previous light microscopy
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Fig. 10–13 10 Early embryo is composed of several blastomeres. Note nuclei of dividing cells in metaphase (me) and anaphase (an). DM degenerating micromere. Bar=5 μm. 11 More advanced embryo contains dividing blastomeres in anaphase (an), which are close either to the remnants of vitellocytes (VC) or the shell (ES). Note lobed nucleus (N) of blastomere. Bar=5 μm. 12 Degeneration of some
micromeres (DM). Note that peripheral blastomeres (DB) seem to be continuous with a thin membraneous layer (ML) which includes also nucleus of a blastomere (NML). Bar=5 μm. 13 Part of the embryo showing four degenerating micromeres (DM) and cell division of blastomere in anaphase (an). Note lobed nucleus (N) and its close association with DM. ML a thin membraneous layer. Bar=2 μm
observations that reported a zygote and several (five to eight) vitellocytes within freshly released eggs of caryophyllideans (Demshin and Dvoryadkin 1980; Protasova et al. 1990; Scholz 1991, 1993), our observations revealed early stages of embryonic development within the intrauterine eggs of K. sinensis. Until now, typical mitotic divisions had never been detected at the ultrastructural level in caryophyllidean eggs. The only evidence for cleavage divisions was the increasing number of blastomeres in advanced stages of embryonic development of W. virilis (Młocicki et al. 2010b). Earlier, Motomura (1929) had pictured mitotic divisions and
cleavage in Archigetes; however, his observations were at the light microscope level. K. sinensis has a type of egg, characteristic of the Caryophyllidea, that also occurs in the monozoic Gyrocotylidea and Amphilinidea as well as in some lower polyzoic groups, e.g. Spathebothriidea, Diphyllobothriidea or Trypanorhyncha (Świderski and Xylander 2000; Conn and Świderski 2008). Their egg is polylecithal and has a thick, hardened shell, and in several orders, there may be an operculum and a small, sometimes inconspicuous, terminal knob or boss at the opposite end. The occurrence of an
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Fig. 14 14 A portion of the embryo surrounded by a thin membraneous layer (ML) with a nucleus (NML). Note nucleus of blastomere undergoing mitotic division in anaphase (an). ES electrondense shell, VC vitelline cell. Bar=5 μm
operculum in caryophyllideans has been a subject of much confusion (see Mackiewicz 1972), largely because it is small and not readily seen when eggs are viewed in utero at the light microscope level. As shown in the present study, intrauterine eggs of K. sinensis have an electrondense shell and an operculum which may be pitted. As described and pictured by Scholz (1991), a small abopercular knob is present at the wider pole of the egg. It is best observed on whole eggs. Apart from the Caryophyllidea, operculate eggs occur also in the Gyrocotylidea, Spathebothriidea and Haplobothriidea; however, the Pseudophyllidea (= Bothriocephalidea and Diphyllobothriidea according to Kuchta et al. 2008) and Trypanorhyncha are polymorphic in this character (Hoberg et al. 1997). There is little information on the ultrastructure of the embryo and associated envelopes of caryophyllid cestodes and no studies that illustrate the embryo, its envelopes and shell in a single TEM micrograph. The structure of a preoncosphere embryo and a fully formed oncosphere of a cestode with polylecithal eggs, but lacking a ciliated embryophore (e.g. Caryophyllidea, Spathebothriidea, some Bothriocephalidea), has been illustrated by Conn and Świderski (2008) who recognized that an embryo at the end of the cleavage divisions is surrounded by outer and inner embryonic envelopes and a vitelline capsule. The hexacanth is surrounded by an oncospheral membrane, situated under an inner envelope, and shell originating from the vitelline capsule. It was not until recently that the latter pattern was described in ultrastructural studies of the intrauterine eggs of the caryophyllidean tapeworm W. virilis family Caryophyllaeidae; see Młocicki et al. (2010b). On the other hand, vitelline capsule or typical embryonic envelopes were not detected in the intrauterine eggs of K.
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sinensis (family Lytocestidae) in the present study, although various blastomere stages ranging from 2 to about 24 cells were observed. An embryo in early cleavage is surrounded by degenerating vitellocytes and an electrondense shell. Vitellocytes were never observed to take part in the formation of the outer embryonic envelope. Typically, the outer envelope of cestode eggs is formed by a fusion of macromeres with the remnants of degenerating vitellocytes (Świderski 1994a, b; Świderski et al. 2005; Młocicki et al. 2010a, b). The late cleavage embryo of K. sinensis is surrounded by a thin membraneous layer and degenerating vitellocytes, both compenents being enclosed within an electrondense shell. Nuclei and degenerating blastomeres occurring within a thin membraneous layer indicate that this surrounding structure may be related to the embryonic envelope (Świderski 1994b). In contrast, the thin membraneous layer of K. sinensis is substantially reduced compared with embryonic envelopes of bothriocephalideans (Świderski 1994b; Świderski et al. 2005). Its ultrastructure may resemble an oncospheral membrane, described between the hexacanth and the inner envelope of fully formed oncospheres (Conn and Świderski 2008). However, its origin and stage of formation is completely different. A typical oncospheral membrane is an anucleated structure and appears at the final stage of embryonic development and originates from delamination of the innermost layer of the inner envelope (Tkach and Świderski 1998; Świderski et al. 2001; Młocicki et al. 2005). Embryonic envelopes were not detected neither during the early development of the caryophyllidean Archigetes appendiculatus by Motomura (1929) and in two species of Khawia by Scholz (1991, 1993); however, these observations were at the light microscope level. The presence of outer and inner embryonic envelopes in the Caryophyllidea was reported only in the intrauterine eggs of W. virilis by Młocicki et al. (2010b). It is of interest that the intrauterine embryonated eggs of another basal tapeworm, spathebothriidean Didymobothrium rudolphii, also do not include embryonic envelopes (Świderski et al. 2010). In contrast, the operculate eggs of another spathebothriidean, Cyathocephalus truncatus, are considered to be fully embryonated already ex utero after releasing of unembryonated eggs into water (Wiśniewski 1932). Glycogen remains as the predominant nutrient within vitellocytes of all caryophyllideans so far examined (Mackiewicz 1968; Świderski and Mackiewicz 1976; Świderski and Xylander 2000; Świderski et al. 2004a, b, 2009). Lipid droplets in degenerating vitellocytes observed in the intrauterine eggs of K. sinensis (present study) were reported recently by Młocicki et al. (2010b) in another caryophyllidean, W. virilis. Both findings are at least unusual as lipid droplets have not been reported previously in mature vitellocytes of caryophyllideans (Mackiewicz 1968; Świderski and Mackiewicz 1976; Świderski et al.
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2004a, b; Bruňanská et al. 2009a) including vitellocytes of K. sinensis (Bruňanská et al. 2009b). The only exception is Atractolytocestus huronensis, that has individual lipid droplets observed occasionaly in the cytoplasm of some of the mature vitellocytes (Bruňanská et al. 2007). The possible explanation supports a hypothesis that degenerating vitellocytes are sites of autolysis and may progressively accumulate waste metabolic products of the developing embryo (Młocicki et al. 2010a; b). However, this presumption needs futher affirmation. As we have found, there are clear signs of degeneration in some blastomeres during early and more advanced stages of the embryonic development in K. sinensis. The degeneration process or apoptosis, results in a great reduction in the number of oncospheral cells, a common characteristic for cestode embryos (Rybicka 1961; Świderski 1968). Degenerating vitellocytes in the intrauterine eggs of K. sinensis contain GER-bodies which were described previously in parasitic flatworms using various terminologies, e. g. lamellar granules, dark concentric bodies, yolk bodies, ribosomal complexes, glycan vesicles (see Młocicki et al. 2011). Such structures have been reported in the mature vitellocytes of other caryophyllideans (Bruňanská et al. 2009a) or spathebothriideans (Bruňanská et al. 2005; Poddubnaya et al. 2006). In W. virilis (Młocicki et al. 2011), GER-bodies were described only in the vitellocytes of newly formed eggs, but not in mature vitellocytes of the vitelline system. In K. sinensis, however, they occur at first in the mature vitellocytes (Bruňanská, unpublished data). GER bodies are supposed to participate in synthesis of glycoproteins or may represent remnants of GER undergoing degeneration and transformation into areas of focal cytoplasmic degradation (Młocicki et al. 2011). The origin of large osmiophilic dense bodies in the cytoplasm of degenerating vitellocytes is unknown and a matter of speculation. They may represent remnants of shell material, highly condensed vitellocyte nuclei or some kind of lysosomal structure. The functional significance of intrauterine embryogenesis in K. sinesis remains unknown. It is of interest that the occurrence of K. sinensis in carp has decreased dramatically since the early 2000s, after A. huronensis appeared in Europe (Majoros et al. 2003; Oros et al. 2004; Kappe et al. 2006; Oros et al. 2009). During the late 1980s and early 1990s, K. sinensis, also an invasive species but from Asia, was the only caryophyllidean parasite found in carp from fishponds in South Bohemia (Scholz 1991). At that time, there was no evidence of intrauterine embryogenesis or ovovivipary in K. sinensis (Demshin and Dvoryadkin 1980; Protasova et al. 1990; Scholz 1991). However, embryonation within the intrauterine eggs has now been found in specimens of K. sinensis collected in 2003 from South Bohemia. Such development may be classified as precocious when com-
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pared with earlier data. This atypical early development may reflect a response to interspecific competition between two invasive cestode species in carp. Indeed, A. huronensis, with its parthenogenetic reproduction (Jones and Mackiewicz 1969; Bruňanská et al. 2011), has been quite successful in colonizing new regions (Oros et al. 2009). It should be noted, however, that intrauterine embryonation was observed in specimens collected in November 2003, when the colder temperatures would be expected to retard rather than accelerate embryo development. It is well-known that oncosphere development is accelerated with increasing temperature in K. sinensis, Diphyllobothrium or Triaenophorus (Kuhlow 1953; Kuperman 1973; Scholz 1991). On the other hand, given that there are no experimental or field data on interspecific competition between K. sinensis and A. huronensis in a stable environment and that multiple cestode infections of carp are common (Oros et al. 2009), further research is required to ascertain if intrauterine embryonation in K. sinensis is related to interspecies competition or other environmental factors. However, it cannot be excluded that differences in the resolution of light and electron microscope and techniques used by previous authors (Demshin and Dvoryadkin 1980; Protasova et al. 1990; Scholz 1991) resulted in misinterpretation of the developmental stages within eggs of Khawia. In utero embryonic development of the caryophyllidean W. virilis (Młocicki et al. 2010b), K. sinensis (present study) and spathebothriidean D. rudolphii (Świderski et al. 2010) differs significantly from that in the bothriocephalideans which release largely either unembryonated operculate eggs (Świderski 1994a, b) or embryonated anoperculate eggs (Świderski et al. 2005). This pattern clearly indicates that embryonic development in the basal orders Caryophyllidea and Spathebothriidea is not identical with that of the Bothriocephalidea, although a great variation exists in embryonation stages of intrauterine eggs in different cestodes, even within the same order as examplified by Bothriocephalidea. Given that evolutionary relationships can often be ascertained from a study of conservative and fundamental structures or developmental stages, comparative embryogenesis may offer insights into the evolutionary relationships among the various cestode groups. Further ultrastructural investigations of early intrauterine development of lower cestodes are needed for a better understanding of reproductive biology and its role in evolution within the Cestoda. Acknowledgements We are grateful to Blanka Škoríková, Dr. Borislav Kostič and the staff of the Laboratory of Electron Micrscopy of the Institute of Parasitology AS CR, České Budějovice, Czech Republic for excellent technical assistance. This research was made within the framework of the joint research project supported by a bilateral agreements on scientific cooperation signed by the the Polish and Slovak Academies of Sciences. The study was supported by the the Grant Agency of the Slovak Republic VEGA (projects no. 2/0018/08 and
1016 2/0047/11). The work was realized within a frame of Centre of Excellence for Parasitology (Code ITMS: 26220120022) based on the support of the Operational Programme “Research & Development” funded from the European regional Development Fund (rate 0.2).
References Bruňanská M (2009) Spermatological characters of the caryophyllidean cestode Khawia sinensis Hsü, 1935, a carp parasite. Parasitol Res 105:1603–1610 Bruňanská M (2010) Recent insights into spermatozoa development and ultrastructure in the Eucestoda. In: Lejeune T, Delvaux P (eds) Human spermatozoa: maturation, capacitation and abnormalities. Nova Science Publishers, Inc., New York, pp 327–354 Bruňanská M, Poddubnaya LG, Dezfuli BS (2005) Vitellogenesis in two spathebothriidean cestodes. Parasitol Res 96:390–397 Bruňanská M, Drobníková P, Oros M (2007) Vitellocytes of the caryophyllidean cestode Atractolytocestus huronensis. Proceed X Int Helminth Symposium. Stará Lesná, Slovak Republic, 9–14 September 2007, p. 14 Bruňanská M, Drobníková P, Oros M (2009a) Vitellogenesis in the cestode Atractolytocestus huronensis Anthony, 1958 (Caryophyllidea: Lytocestidae). Parasitol Res 105:647–654 Bruňanská M, Drobníková P, Oros M (2009b) Vitellocytes of the caryophyllidean cestode Khawia sinensis Hsü, 1935, a carp parasite. Mikroskopia 2009. Stará Lesná, Slovak Republic, 25– 26 March, 2009, p. 17 Bruňanská M, Nebesářová J, Oros M (2011) Ultrastructural aspects of spermatogenesis, testes and vas deferens in the parthenogenetic tapeworm Atractolytocestus huronensis Anthony, 1958 (Cestoda: Caryophyllidea), a carp parasite from Slovakia. Parasitol Res 108:61–68 Calentine RL (1984) Biology of Archigetes (Caryophyllaeidae) in Limnodrilus hoffmeisteri (Tubificidae). Proc Helminthol Soc Wash 51:109–112 Conn DB, Świderski Z (2008) A standardized terminology of the embryonic envelopes and associated developmental stages of tapeworms (Platehelminthes: Cestoda). Folia Parasitol 55:42–52 Demshin NI, Dvoryadkin VA (1980) Biology of Khawia sinensis Hsü, 1935 (Caryophyllidea, Cestoda) a parasite of Cyprinus carpio haematopterus. Hydrobiologia Zh 16:77–82 (In Russian) Hoberg EP, Mariaux J, Justine J-L, Brooks DR, Weekes PJ (1997) Phylogeny of the orders of the Eucestoda (Cercomeromorphae) based on comparative morphology: historical perspectives and a new working hypothesis. J Parasitol 83:1128–1147 Jones AW, Mackiewicz JS (1969) Naturally occurring triploidy and parthenogenesis in Atractolytocestus huronensis Anthony (Cestoidea: Caryophyllidea) from Cyprinus carpio L. in North America. J Parasitol 55:1105–1118 Kappe A, Seifert T, El-Nobi G, Bräuer G (2006) Occurrence of Atractolytocestus huronensis (Cestoda: Caryophyllaeidae), in German pond-farmed common carp Cyprinus carpio. Dis Aquat Org 70:255–259 Kennedy CR (1965) Taxonomic studies on Archigetes Leuckart, 1878 (Cestoda, Caryophyllidea). Parasitology 55:439–451 Kuchta R, Scholz T, Brabec J, Bray RA (2008) Suppression of the tapeworm order Pseudophyllidea (Platyhelminthes:Eucestoda) and the proposal of two new orders, Bothriocephalidea and Diphyllobothriidea. Int J Parasitol 38:49–55 Kuhlow F (1953) Űber die Entwicklung und Anatomie von Diphyllobothrium dendriticum Nitzsch 1824. Z Parasitenkd 16:1–35 Kuperman BI (1973) Tapeworms of the genus Triaenophorus, parasites of fishes. Leningrad, Izdateľstvo Nauka, 208 pp (In Russian,
Parasitol Res (2012) 110:1009–1017 English translation (1981)). Amerind Publishing Co. Pvt. Ltd, New Delhi, p 222 Mackiewicz JS (1968) Vitellogenesis and egg-shell formation in Caryophyllaeus laticeps (Pallas) and Caryophyllaeoides fennica (Schneider) (Cestoidea: Caryophyllidea). Z Parasitenkd 30:18–32 Mackiewicz JS (1972) Caryophyllidea (Cestoidea): a review. Exp Parasitol 31:417–512 Mackiewicz JS (2003) Caryophyllidea (Cestoidea): molecules, morphology and evolution. Acta Parasitol 48:143–154 Majoros G, Gy C, Molnár K (2003) Occurrence of Atractolytocestus huronensis Anthony, 1958 (Cestoda: Caryophyllaeidae), in Hungarian pond-farmed common carp. Bull Eur Ass Fish Pathol 23:167–175 Młocicki D, Świderski Z, Eira C, Miquel J (2005) An ultrastructural study of embryonic envelope formation in the anoplocephalid cestode Mosgovoyia ctenoides (Railliet, 1890) Beveridge, 1978. Parasitol Res 95:243–251 Młocicki D, Świderski Z, Conn DB (2010a) Ultrastructure of the early embryonic development of Corallobothrium fimbriatum (Cestoda: Proteocephalidea). J Parasitol 96:839–846 Młocicki D, Świderski Z, Mackiewicz JS, Ibraheem MH (2010b) Ultrastructure of intrauterine eggs: evidence of early ovoviviparity in the caryophyllidean cestode Wenyonia virilis Woodland, 1923. Acta Parasitol 55:349–358 Młocicki D, Świderski Z, Mackiewicz JS, Ibraheem MH (2011) Ultrastructural and cytochemical studies of GER-bodies in the intrauterine eggs of Wenyonia virilis Woodland, 1923 (Cestoda, Caryophyllidea). Acta Parasitol 56:40–47 Motomura I (1929) On the early development of monozoic cestode, Archigetes appendiculatus, including the oogenesis and fertilization. Annot Zool Jap 12:109–129 Oros M, Hanzelová V, Scholz T (2004) The cestode Atractolytocestus huronensis (Caryophyllidea) continues to spread in Europe: new data on the helminth parasite of the common carp. Dis Aquat Org 62:115–119 Oros M, Hanzelová V, Scholz T (2009) Tapeworm Khawia sinensis: review of the introduction and subsequent decline of a pathogen of carp, Cyprinus carpio. Vet Parasitol 164:217–222 Poddubnaya LG, Gibson DI, Świderski Z, Olson PD (2006) Vitellocyte ultrastructure in the cestode Didymobothrium rudolphi (Monticelli, 1890): possible evidence for the recognition of divergent taxa within the Spathebothriidea. Acta Parasitol 51:255–263 Protasova EN, Kuperman BI, Roytman VA, Poddubnaya LG (1990) Caryophyllids of the fauna in SSSR. Nauka, Moscow, p 238, In Russian Rybicka K (1961) Cell reduction in the embryonic development of the cestode Diorchis ransomi Schultz, 1940. Nature 192:771–772 Scholz T (1991) Early development of Khawia sinensis Hsü, 1935 (Cestoda: Caryophyllidea), a carp parasite. Folia Parasitol 38:133–142 Scholz T (1993) On the development of Khawia baltica Szidat, 1942 (Cestoda: Lytocestidae), a parasite of tench, Tinca tinca (L.). Folia Parasitol 40:99–103 Świderski Z (1968) An electron microscopic evidence of the degeneration of some micromeres during embryonic development of the cestode Catenotaenia pusilla (Goeze, 1782) (Cyclophyllidea, Catenotaeniidae). Zool Polon 18:469–474 Świderski Z (1994a) Origin, differentiation and ultrastructure of egg envelopes surrounding the coracidia of Bothriocephalus clavibothrium. Acta Parasitol 39:73–81 Świderski Z (1994b) Homology and analogy of egg enevelopes surrounding the coracidia of Bothriocephalus clavibothrium and miracidia of Schistosoma mansoni. Acta Parasitol 39:123–130 Świderski Z, Bruňanská M, Poddubnaya LG (2004a) Ultrastructural and cytochemical studies on vitellogenesis in the caryophyllidean
Parasitol Res (2012) 110:1009–1017 cestode Caryophyllaeus laticeps. Proceed. IX Eur. Multicolloq. Parasitol. Valencia, Spain, 18–23 July 2004, p. 602 Świderski Z, Mackiewicz JS (1976) Electron microscope study of vitellogenesis in Glaridacris catostomi (Cestoidea: Caryophyllidea). Int J Parasitol 6:61–73 Świderski Z, Xylander WER (2000) Vitellocytes and vitellogenesis in cestodes in relation to embryonic development, egg production and life cycle. Int J Parasitol 30:805–817 Świderski Z, Ndiaye PI, Tkach V, Miquel J, Marchand B, Chomicz L, Sereda MJ (2001) Ultrastructural study of the embryonic development of the anoplocaphalid cestode Anoplocephaloides dentata, an intestinal parasite of Arvicolidae rodents. I. Egg envelope formation. Acta Parasitol 46:171–185 Świderski Z, Bruňanská M, Poddubnaya LG, Mackiewicz JS (2004) Cytochemical and ultrastructural study on vitellogenesis in caryophyllidean cestode Khawia armeniaca (Cholodkovski, 1915). Acta Parasitol 49:16–24 Świderski Z, Bruňanská M, Młocicki D, Conn DB (2005) Ultrastructure of the oncospheral envelopes in the pseudophyllidean Eubothrium salvelini (Schrank, 1790). Acta Parasitol 50:312–318
1017 Świderski Z, Młocicki D, Mackiewicz JS, Miquel J, Ibraheem MH, Bruňanská M (2009) Ultrastructure and cytochemistry of vitellogenesis in Wenyonia virilis Woodland, 1923 (Cestoda, Caryophyllidea). Acta Parasitol 54:131–142 Świderski Z, Gibson DI, Santos MJ, Poddubnaya LG (2010) Ultrastructure of the intrauterine eggs of Didymobothrium rudolphi (Monticelli, 1890) (Cestoda, Spathebothriidea, Acrobothriidae) and its phylogenetic implications. Acta Parasitol 55:254–269 Thiéry J-P (1967) Mise en évidence des polysaccharides sur coupes fines en microscopie électronique. J Microsc 6:987–1018 Tkach VV, Świderski Z (1998) Differentiation and ultrastructure of the oncospheral envelopes in the hymenolepidid cestode Staphylocystoides stefanskii (Żarnowski, 1954). Acta Parasitol 43:222– 231 Wiśniewski LW (1930) Das Genus Archigetes R. Leuck. Eine Studie zur Anatomie, Histogenese, Systematik und Biologie. Mém Acad Pol Sci Lett Class Sci Mathém Natur Ser B Sci Nat 2:160 Wiśniewski LW (1932) Cyathocephalus truncatus Pallas. II. Allgemeine Morphologie. Bull Int Acad Pol Sci. Class Sci Mathem Natur, Ser B: Sciences Nat (II):311–327
