A comparative study of the scoleces of monozoic tapeworms (Cestoda: Caryophyllidea), parasites of catostomid and cyprinid fishes (Teleostei: Cypriniformes) in the Nearctic Region, was carried out using light and scanning electron microscopy. Scoleces of 22 genera of North American caryophyllideans were characterised and their importance for taxonomy, classification and phylogenetic studies was critically reviewed. Nearctic genera exhibit a much higher variation in the shape and form of scoleces compared with taxa in other biogeographical regions. The following basic scolex types can be recognised in Nearctic caryophyllideans: monobothriate (Promonobothrium Mackiewicz, 1968), loculotruncate (Promonobothrium, Dieffluvium Williams, 1978), bothrioloculodiscate (Archigetes Leuckart, 1878, Janiszewskella Mackiewicz et Deutsch, 1976, Penarchigetes Mackiewicz, 1969, Pseudoglaridacris Oros, Uhrovič et Scholz, 2018), fixomegabothriate (Capingens Hunter, 1927), bulbate and bulboacuminate (Atractolytocestus Anthony, 1958), cuneiloculate (Hypocaryophyllaeus Hunter, 1927, Rowardleus Mackiewicz et Deutsch, 1976, Spartoides Hunter, 1929), biacetabulate, bulboloculate, bothrioloculodiscate (Biacetabulum Hunter, 1927), tholate (Hunterella Mackiewicz et McCrae, 1962), cuneifimbriate (Khawia Hsü, 1935), cuneiform (Calentinella Mackiewicz, 1974, Caryophyllaeides Nybelin, 1922, Edlintonia Mackiewicz, 1970), hastate (Pseudolytocestus Hunter, 1929), loculotholate (Bialovarium Fischthal, 1953, Pliovitellaria Fischthal, 1951), and cuneiformoloculate (Glaridacris Cooper, 1920, Isoglaridacris Mackiewicz, 1965). The same type of scolex may be shared by species of different genera or families and species of the same genus can have a scolex of conspicuously different morphology, e.g. in Promonobothrium. Scolex morphology may be therefore of limited use in generic designation.

Spermiogenesis in progenetic and adult stages of Archigetes sieboldi Leuckart, 1878, a tapeworm parasitic in oligochaetes and fish respectively, has been examined using transmission electron microscopy and cytochemical staining for glycogen. General pattern of spermiogenesis is essentially like that of other caryophyllideans, i.e., apical dense material in the zone of differentiation in the early stages of spermiogenesis, rotation of free flagellum and a flagellar bud, and proximo-distal fusion. Interestingly, rotation of a free flagellum and flagellar bud to the median cytoplasmic process (MCP) has been observed unconventionally at > 90° only in progenetic stages. Typical striated roots associated with the centrioles occur rarely in A. sieboldi, and only in form of faint structures in advanced stages of spermiogenesis. In contrast to most caryophyllideans studied to date, penetration of the nucleus into the spermatid body has started before the fusion of the free flagellum with the MCP. This feature has been reported rarely but exclusively in the family Caryophyllaeidae. The unipartite mature spermatozoon of A. sieboldi is composed of one axoneme of the 9 + '1' trepaxonematan pattern with its centriole, parallel nucleus, and parallel cortical microtubules which are situated in a moderately electron-dense cytoplasm with glycogen particles. An unusual arrangement of cortical microtubules in the two parallel rows in region I of the spermatozoon is described here for the first time in the Caryophyllidea. Ultrastructural data on spermiogenesis and the spermatozoon in A. sieboldi from tubuficids and carp are compared and discussed with those in other caryophyllideans and/or Neodermata.

Vitellogenesis and vitellocytes of Cainocreadium labracis were studied by transmission electron microscopy (TEM) and TEM cytochemistry. Four developmental stages were distinguished during vitellogenesis: (I) stem cell of high nucleo-cytoplasmic ratio; (II) early differentiation with chief activity focused on the beginning of protein synthesis and shell globule formation; (III) advanced differentiation with rapid intensification of protein synthesis, progressive fusion of single shell globules into large globule clusters, and formation of unsaturated lipid droplets surrounded by β-glycogen particles; and (IV) mature vitellocyte. Early vitellogenesis with vitellocyte maturation consists of: (1) increase in cell volume; (2) increased development of large, parallel cisternae of GER with production of proteinaceous granules; (3) development of small Golgi complexes that package granules; and (4) within vacuoles, progressive enlargement of proteinaceous granules into shell globule clusters formed during vitellogenesis. Three types of inclusions accumulate in large amounts in mature vitelline cells: (1) shell globule clusters, important component in the formation of egg shell; (2) numerous unsaturated lipid droplets. Though fewer, there are also diphasic droplets consisting of saturated and unsaturated lipids in the same droplet, and (3) a relatively small amount of β-glycogen particles, usually surround a few groups of lipid droplets. The β-glycogen and lipid droplets are nutritive reserves for embryogenesis. General pattern and functional ultrastructure of vitellogenesis greatly resemble those observed in some lower cestodes, such as bothriocephalideans and diphyllobothrideans. Variations and differences in the amount of lipids and of glycogen during vitellogenesis in lower cestodes and other trematodes are compared and discussed.

Spermatozoon formation in Caryophyllaeides fennica (Schneider, 1902) is characterised by the following: (1) apical electron-dense material in the zone of differentiation, (2) typical striated roots situated unconventionally in opposite directions in early stages of spermiogenesis, (3) intercentriolar body composed of three electron-dense and two electron-lucent plates, (4) free flagellum and a flagellar bud that correspond to a greatly reduced flagellum and (5) rotation of free flagellum and a flagellar bud to the median cytoplasmic process at 90°. The development of two flagella of significantly unequal length clearly supports a derived form of spermiogenesis in the Caryophyllidea. New for cestodes is a finding of two additional striated roots situated opposite each other, in conjunction with both the flagellar bud and free flagellum. Mutual position of additional striated roots and typical striated roots is parallel in early stages and perpendicular in advanced stages of spermiogenesis. A complete proximodistal fusion gives rise to a mature spermatozoon consisting of one axoneme, parallel cortical microtubules, a nucleus and a moderately electron-dense cytoplasm with glycogen particles, detected by a technique of Thiéry (J Microsc 6:987–1018, 1967), in the principal regions (II, III, IV). Electron tomography analysis of the free flagellum and one axoneme of a mature spermatozoon of C. fennica provides clear evidence, for the first time, that two tubular structures are present in the central axonemal electron-dense core. Phylogenetically important aspects of spermiogenesis of the Caryophyllidea with one axoneme, and other cestodes with one or two axonemes, are briefly reviewed and discussed.

Spermatological characters of Dictyocotyle coeliaca Nybelin, a unique endoparasitic monogenean from the body cavity of the ray Amblyraja radiata (Elasmobranchii: Rajidae), was investigated by means of scanning and transmission electron microscopy for the first time. The process of the spermatozoon formation begins with the appearance of the differentiation zone which contains two centrioles. Subsequently developed two free flagella rotate to lie parallel before their fusing. After fusion, both the mitochondrion and nucleus migrate alongside the axonemes. Spermatids are formed within parallel cytoplasmic canals. During late spermiogenesis, an electron-dense spiral end-piece is formed proximally to the centriolar region of some spermatids. At the end of spermiogenesis, this end-piece is separated by a plasma membrane from the late spermatid and remains in the residual cytoplasm when spermatozoa are released into the testis lumen. The mature spermatozoon of D. coeliaca contains two parallel axonemes with the 9 + “1” trepaxonematan pattern, mitochondrion, nucleus, parallel cortical microtubules, and electron-dense granules. Especially the presence of electron-dense granules, occurring frequenly in the spermatozoa of endoparasitic flatworms, may indicate an adaptation to endoparasitic lifestyle in D. coeliaca . The anterior extremity of the male gamete contains one centriolar derivative, a small component of the second centriolar derivative and anterior extremity of the mitochondrion. The posterior extremity of the mature spematozoon exhibits tubular elements of the disorganized axoneme. Variations of the spermatozoon ultrastructural characters within monocotylid monogeneans and possible evolutionary significance of glycogen in sperm to the endoparasitic habit are discussed.

Professor Zbigniew (Bob) Kabata, renowned, highly respected Polish and Canadian parasitologist died on 4th July 2014 in Nanaimo, British Columbia, Canada, at the age of 90. He is best known as one of the distinguished pioneers in the fields of fish parasitology and fish diseases. Like the rest of the parasitological community, we too grieve at his passing and will miss his wise counsel on the Editorial Board of Acta Parasitologica, where he served for many years. When reviewing manuscripts for publication, his expertise in parasitology was legendary and his guidance, constructive comments, meticulous attention to detail and his goodwill were always greatly appreciated by authors and our Editorial Board. As few before him, he was a scholar extraordinaire with a rich, multifaceted personal history: Polish war hero, outstanding intellectual, famous poet, writer, translator, scientific administrator – and above all – eminent parasitologist. Prof. Kabata was born March 17, 1924 in the Carpathian town of Jaremcze (Yaramche), previously in Poland, now in Western Ukraine since World War II. With the invasion of Poland by Germany in 1939, he left school, the Marshal Józef Piłsudski Military Academy in Lwów (Lvov) and joined the Armia Krajowa, the Polish underground resistance (guerrilla) army. He fought the Nazis (1940–1945), became in his own words “an accomplished machine-gunner”, led raids, was cited for bravery several times and wrote patriotic poems and partisan songs. Years later (1964) in Aberdeen, Scotland, he was to write his most famous poem “Paying Tribute to the Underground Army”; it can be found engraved on memorials and plaques throughout Poland. Poland’s highest decoration, Grand Commander (with star) of the Order of Polonia Restituta was presented to him (1996) for his heroism and distinguished war record that included: Partisan Cross, War Order of Virtuti Militari (ClassV), Home (Underground) Army Cross, Cross of Valour (twice), Polish Army 1939–1945 War Medal (two bars), Gold Medal for Contributions to the Defensivness of the Country, Medal Pro Memoria and Polish Armed Forces Gold Medal. After the Soviet invasion of Poland, he escaped to Italy, rejoined the Free Polish Force with the British 8th army and after the war moved to England (1946). After 6 months of vocational training in marine fisheries he became a deck-hand on a North Sea trawler out of Aberdeen. As a deep-sea fisherman he became fascinated with the science of marine fisheries, an area of study that he would pursue the rest of his life. He subsequently enrolled in the University of Aberdeen, Department of Zoology (1951) and graduated (1955) with 1-st Class Honours BSc in Zoology. Shortly thereafter in Aberdeen he joined Scotland’s Marine Laboratory (Scottish Department of Agriculture and Fisheries) as parasitologist and founded the Parasitology Unit. He was awarded the Ph.D from IN MEMORIAM

The vitellarium of the invasive caryophyllidean tapeworm Khawia sinensis Hsü, 1935 from carp Cyprinus carpio L. was examined by means of transmission electron microscopy and cytochemical staining for glycogen with periodic acid–thiosemicarbazide–silver proteinate (PA-TSC-SP). A vitellarium consists of numerous follicles of irregular size that are interconnected by a net of vitelline ducts. Vitelline follicles are composed of vitelline cells at various stages of development that are interconnected by interstitial tissue. Vitelline follicles are surrounded by a cytoplasmic sheath associated with an intercellular matrix. Extensive development of the granular endoplasmic reticulum and Golgi complexes are both involved in the production of shell globules/shell globule clusters and characterise cytodifferentiation of vitellocytes. Nuclear and nucleolar transformation lead to the formation and storage of intranuclear glycogen, a feature specific for the Caryophyllidea. Newly observed within the mature vitellocytes of Khawia sp. is the presence of lamellar bodies and a few lipid droplets. These cytoplasmic inclusions first occur in the mature cells within the follicles and persist in the vitelline cells within vitelloducts and intrauterine eggs. Two types of lamellar bodies are detected: regular lamellar-structured body and irregular lamellar-structured body. None of the lamellar bodies are membrane bound. Results of the present study indicate that the formation of lamellar bodies may be closely related to the endoplasmic reticulum or shell globule clusters. Some of the shell globule clusters are transformed into lamellar body clusters. Ultrastructural features of vitellocytes in K. sinensis are compared with those of other monopleuroid, polypleuroid, and strobilated cestodes.

Reinvestigation of vitellogenesis in the caryophyllidean cestode Caryophyllaeus laticeps (Pallas, 1781) has been performed using light microscope (LM) and transmission electron microscopy (TEM), and cytochemical staining with periodic acid-thiosemicarbazide-silver proteinate (PA-TSC-SP) for glycogen. Vitellogenesis is generally similar to that reported in the past, however, some new observations were made. The present study reveals the first evidence of: (i) interstitial tissue in the vitelline follicles, (ii) lipid droplets in maturing and mature vitellocytes from vitelline follicles, and (iii) lamellar bodies in vitellocytes from the vitelloduct in C. laticeps. Projections of interstitial tissue surround each vitellocyte and the follicle periphery. The perinuclear cytoplasm of the interstitial tissue contains granular endoplasmic reticulum and vesicles of various size and density. Cytoplasmic osmiophobic lipid droplets and lamellar bodies, previously believed to be absent in most caryophyllid cestodes, are readily apparent in vitellocytes of C. laticeps. The origin and presumed function of these inclusions are discussed. On the other hand, the formation and storage of massive amounts of glycogen in the nucleus and large amounts in the cytoplasm of mature vitelline cells are similar to the condition found in other caryophyllids. Results are compared and contrasted with previous studies on vitellogenesis in other monopleuroid cestodes (Amphilinidea and Gyrocotylidea) as well as polypleuroid cestodes (Spathebothriidea) and the remaining strobilated Eucestoda.

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 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.

Vitellogenesis in the caryophyllidean tapeworm Archigetes sieboldi Leuckart, 1878, from carp Cyprinus carpio L. in Slovakia, has been examined using transmission electron microscopy and cytochemical staining with periodic acid-thiosemicarbazide-silver proteinate (PA-TSC-SP) for glycogen. Vitelline follicles extend in two lateral bands in the medullary parenchyma along both sides of the monozoic body. They are surrounded by an external basal lamina and contain vitellocytes and an interstitial tissue. The general pattern of vitellogenesis is essentially like that of other caryophyllideans. It involves four stages: immature, early maturing, advanced maturing cells and mature vitellocytes. During vitellogenesis, a continuous increase in cell volume is accompanied by an extensive development of cell components engaged in shell globule formation, e. g. granular endoplasmic reticulum and Golgi. Shell globule clusters are membrane-bound. Nuclear and nucleolar transformation are associated with formation and storage of large amounts of intranuclear glycogen, a very specific feature of the Caryophyllidea. For the first time, (a) additional vitelline material in Archigetes is represented by lamellar bodies and (b) lipid droplets are described in the mature vitellocytes from vitelline follicles and vitelloduct of the Caryophyllidea. Our results indicate that there may be a double origin of lamellar bodies: either from the endoplasmic reticulum or through transformation of shell globule/shell globule clusters. Lamellar body clusters and some single lamellar bodies appear to have a membrane. Other ultrastructural features of vitellogenesis and/or vitellocyte in A. sieboldi from its vertebrate (fish) and invertebrate (oligochaete) hosts are briefly compared and contrasted with those in other caryophyllideans and/or Neodermata.

Tapeworms (Cestoda, Platyhelminthes) are a highly diversified group of parasites that can have significant veterinary importance as well as medical impact as disease agents of human alveococcosis, hydatidosis, taeniosis/cysticercosis/neurocysticercosis, hymenolepidosis or diphyllobothriasis. Because of their great diversity, there has been keen interest in their phylogenetic relationships to other obligate parasitic platyhelminthes, as well as within the group itself. Recent phylogenetic analyses of cestodes, however, have focused on morphological, molecular, life cycle, embryology and host-specificity features and conspicuously omitted inclusion of karyological data. Here we review the literature from 1907 to 2010 and the current status of knowledge of the chromosomes and cytogenetics within all of the cestode orders and place it within an evolutionary perspective. Karyological data are discussed and tabulated for 115 species from nine eucestode orders with ideograms of 46 species, and a comparison of cytogenetic patterns between acetabulate and bothriate cestode lineages is made. Attention is drawn to gaps in our knowledge for seven remaining orders and cestodarian groups Gyrocotylidea and Amphilinidea. Among the cytogenetic aspects covered are: chromosome number, triploidy, classical karyotype cytogenetics (banding patterns, karyotype asymmetry, secondary constrictions), as well as advanced karyotype techniques allowing location of genes on chromosomes by fluorescence in situ hybridization. We demonstrate that further progress in cestode karyosystematics rests with new molecular approaches and the application of advanced cytogenetic markers facilitating intimate karyotype analysis.

Ultrastructural and cytochemical characteristics of GER-bodies observed in the vitellocyte cytoplasm of the intrauterine eggs of the caryophyllidean cestode Wenyonia virilis are described. In this species GER-bodies were observed only in the cytoplasm of vitellocytes, surrounded by a newly formed egg-shell. They are composed of spherical areas of condensed, electron-dense cytoplasm which contains concentrically arranged parallel lamellae of granular endoplasmic reticulum (GER), forming characteristic balls of different sizes. Each GER-body is surrounded by numerous free ribosomes, polyribosomes, α-glycogen rosettes and large mitochondria. Results of cytochemical analysis by means of PATSC-SP test for polysaccharides indicated that glycogen is absent within the GER-bodies, however, a strongly positive reaction was observed only in large aggregations of α-glycogen rosettes and β-glycogen particles, localised usually near GER-bodies.

The first description of vitellogenesis in the Diphyllidea is presented in this paper. Though the type of vitellogenesis and mature vitellocyte in Echinobothrium euterpes appear to be unique among the Eucestoda, however, they somewhat resemble that observed in the two orders of the lower cestodes, Tetraphyllidea and Proteocephalidea. Vitellocyte maturation is characterized by: (1) an increase in cell volume; (2) extensive development of short, parallel, frequently concentric cisternae of GER that produce dense proteinaceous granules; (3) development of Golgi complexes engaged in packaging this material; (4) progressive formation of saturated lipid droplets; their continuous enlargement and fusion; (5) formation of small accumulations of glycogen particles scattered between and among lipid droplets in the cytoplasm of maturing vitellocytes; (6) concentration of dense proteinaceous granules in the peripheral layer of cytoplasm, around the cell plasma membrane; and (7) vacuolization of cytoplasm of mature vitellocytes accompanied by a rapid increase in its volume. A new, unreported type of dense proteinaceous granules, situated around the limiting plasma membranes of mature vitellocytes, is described. Vitellogenesis evidently differs from that with typical shell-globules and shell-globule clusters previously reported in other taxa of lower cestodes. Cytochemical staining with periodic acidthiosemicarbazide-silver proteinate for glycogen indicates a strongly positive reaction for glycogen particles between and around large unsaturated lipid droplets of the maturing and mature vitellocytes. Some hypotheses concerning the interrelationship between this pattern of vitellogenesis, possible mode of egg formation, embryonic development and diphyllidean life cycle, and their phylogenetic implications are drawn and discussed.

Ultrastructural evidence for early intraurerine embryonic development of Wenyonia virilis is presented. At the initial stage of egg formation, the fertilized oocyte or ovum is surrounded by numerous vitellocytes and newly formed eggshell. Individual vitellocytes undergo progressive fusion into a vitelline syncytium. During cleavage divisions, three types of blastomeres are formed: macromeres, mesomeres and micromeres. Two large macromeres contain a large nucleus with spherical nucleolus and numerous small heterochromatin islands dispersed in moderately electron-dense nucleoplasm. The granular cytoplasm shows a few large mitochondria. Medium-sized mesomeres contain a spherical nucleus with numerous heterochromatin islands, adjacent to the nuclear envelope, and a prominent electron-dense nucleolus. Their nuclei are embedded in granular cytoplasm with a few large and numerous small mitochondria and Golgi complexes. The small micromeres are characterized by presence of spherical nucleoli with large areas of highly condensed heterochromatin and a few islands of granular electron-lucent nucleoplasm. Their granular cytoplasm shows a few small lipid droplets and several spherical mitochondria. Majority of micromeres give rise to the hexacanth but many of them also undergo degeneration or apoptosis. Both mesomeres and macromeres are engaged in the formation of the oncospheral envelopes. The outer envelope is formed by a fusion of two macromeres whereas the inner envelope originates from a fusion of mesomeres. The intrauterine eggs of W. virilis usually contain an embryo at the early preoncopheral phase of development and possesses three primary envelopes: (1) thick eggshell; (2) thin cytoplasmic layer of the outer envelope and (3) inner envelope. Based on embryonic development, egg type and life-cycle characteristics, caryophyllideans tend to show closer affinities to spathebothriideans than to the former pseudophyllideans.

A comparative study of the scoleces of caryophyllidean tapeworms (Cestoda: Caryophyllidea), parasitic in cypriniform fishes in the Palaearctic Region, was carried out using light and scanning electron microscopy. Three-dimensional pictures of the scoleces of 18 species of caryophyllidean cestodes of the Capingentidae (1 species), Caryophyllaeidae (7) and Lytocestidae (10), and outlines of the scoleces and anterior extent of the testes and vitelline follicles of 19 Palaearctic taxa were documented. Both species of Atractolytocestus Anthony, 1957 possess a bulboacuminate scolex, whereas species of Archigetes Leuckart, 1876 have fossate scoleces of the bothrioloculodiscate type, with loculi, bothrium-like depressions and an apical disc. Breviscolex orientalis Kulakovskaya, 1962, the only member of the Capingentidae, has a cuneiform scolex, as do both taxa of the lytocestid genus Caryophyllaeides Nybelin, 1922. The scoleces of two species of Caryophyllaeus Gmelin, 1790 are flabellate, whereas that of the congeneric C. fimbriceps Annenkova-Chlopina, 1919 is cuneicrispitate. Khawia Hsü, 1935, the most specious Palaearctic genus, with seven taxa that we consider to be valid, has the highest diversity in scolex morphology: semi-bulbate, flabellate, cuneiform, cuneifimbriate, truncated cuneiform-flabellate and festoon-like. Species of Monobothrium Nybelin, 1922 have either a digitiform scolex with widened posterior part or cuneiform, with lateral auricular extensions. Paracaryophyllaeus gotoi (Motomura, 1927) is characteristic in its possessing a bulbate scolex, whereas Paraglaridacris limnodrili (Yamaguti, 1934) has a fossate scolex of the bulboloculate type with bothrium-like depressions and feebly developed lateral loculi. Anterior extent of the testes and vitelline follicles and their mutual position show a somewhat higher variability than scolex shape, with intraspecific variation in some taxa, such as Atractolytocestus sagittatus (Kulakovskaya et Akhmerov, 1965), B. orientalis, Khawia armeniaca (Cholodkovsky, 1915) and K. sinensis Hsii, 1935. Based on scolex morphology and relative position of the anterior testes and vitelline follicles, a key is provided to facilitate the routine identification of 20 Palaearctic caryophyllidean taxa.

Vitellogenesis in Wenyonia virilis was examined by transmission electron microscopy (TEM), including the cytochemical detection of glycogen at the ultrastructural level with the periodic acid-thiosemicarbazide-silver proteinate (PA-TSC-SP) technique. Mature vitelline follicles have cells in various stages of development, progressing from immature cells of gonial type near the periphery of the follicle to maturing and mature vitellocytes towards the centre. Maturation is characterized by: (1) increase in cell volume; (2) increase in nuclear surface area restoring the N/C (nucleo-cytoplasmic) ratio; (3) nucleolar transformation; (4) extensive development of parallel cisternae of GER, the shell-protein producing units; (5) development of Golgi complexes, engaged in shell-granule/shell-globule formation and packaging; (6) synthesis and storage of glycogen in the cytoplasm; (7) simultaneous, independent formation and storage of intranuclear glycogen; (8) continuous fusion of small shell-granules into larger shell-globules and fusion of these into large shell-globule clusters with a progressive increase in the number and size of the latter; and (9) disintegration of GER in the medial layer of vitellocyte cytoplasm, degenerative changes and accumulation of glycogen and shell-globule clusters within the cytoplasm. The functional significance of numerous shell-globule clusters and the relatively small amount of nuclear and cytoplasmic glycogen is analysed. Unlike vitellogenesis of other caryophyllids, the nuclear glycogen of mature vitellocytes in W. virilis is randomly dispersed in the nucleoplasm and never forms a high central accumulation, the so-called “nuclear vacuole”. The nutritive function of vitellocytes appears greatly reduced in W. virilis, a fact perhaps related to the intrauterine development of the early embryos. The ultrastructure of vitellogenesis in W. virilis is compared with that in other lower cestodes, both monozoic and polyzoic. Conclusions concerning interrelationships of the vitellogenesis pattern of the ultrastructural cytochemistry of mature vitellocytes of W. virilis to intrauterine embryonation, absence of uterine glands and an extensive uterus characteristic for this species, are drawn and discussed.

Transmission (TEM) and scanning (SEM) electron microscope methods were used to study the fine structure of the cirrus, cirrus sac, internal seminal vesicle, ejaculatory duct, prostate glands and cirrus armature of Echinophallus wageneri (Monticelli, 1890) and Paraechinophallus japonicus (Yamaguti, 1934) (Bothriocephallidea: Echinophallidae). The cirrus sac of these species has two unique ultrastructural features: a thick wall with two bands of muscles and prominent, rooted hard structures. Rare traits echinophallids share with diphyllobothriideans are microtriches on the ejaculatory duct and with spathebothriideans, well-developed unicellular prostate glands outside the cirrus sac. Because there is a similarity of cirrus armature and rostellar hooks in having a tegumental localisation and in having a heterogenous structure of the blade and root, a cortex, a central pulp region and a recurved apex, these structures are named "modified hooks" instead of spines. They also have a spiral arrangement; no base plate was observed. True spines, as found in trematodes, are between the surface and basal plasma membrane of the external syncytial layer of the tegument, rest on the basal plasma membrane of the distal epithelial cytoplasm, show a homogeneous electron-dark crystalline appearance and are covered by the surface plasma membrane. Aside from the characteristic hooks on the scolex of various cestodes, we see no evidence that would preclude the development of still other specialised structures, such as these modified hooks, from microtriches. In spite of the absence of studies on the development of modified hooks from the cirrus of echinophallids and/or its consideration as derived from microtriches, we assume that like microtriches, formation of modified hooks is from tegumental bodies and therefore they are derivative structures of the cestode tegument.

Phylogenetic relationships of all genera of the order Caryophyllidea, possibly the earliest branching group of true tapeworms (Platyhelminthes: Eucestoda) and the only one that is monozoic, have been assessed for the first time. Results of this cladistic analysis, inferred from 30 unweighted morphological characters, are only partly congruent with the existing classification, which consists of four families based on the position of the inner longitudinal muscles in relation to the internal genital organs. Whereas all but five genera of the Caryophyllaeidae form a monophyletic clade, members of the Capingentidae are split, occurring within six unrelated groups. The Lytocestidae is also paraphyletic, as some genera appear in four unrelated clades. Archigetes appears in a derived clade, indicating that its direct (monoxenous) life-cycle involving only tubificid oligochaetes is secondarily derived and not plesiomorphic among the Eucestoda, as postulated by some authors.

The ultrastructure of spermiogenesis in Wenyonia virilis Woodland, 1923, a caryophyllaeid cestode from the silurid Nile fish Synodontis schall (Bloch et Schneider, 1801), is described by means of transmission electron microscopy (TEM) for the first time. Spermiogenesis follows the characteristic caryophyllidean type and is initiated by the formation of a differentiation zone. This area, delimited at its base by a ring of arching membranes and bordered by cortical microtubules, contains two centrioles associated with typical striated rootlets with a reduced intercentriolar body between them. The apical area of the differentiation zone exhibits electron-dense material that is present only during the early stages of spermiogenesis. Only one of the centrioles develops into a free flagellum that grows at an angle of >90° in relation to the cytoplasmic extension. Spermiogenesis is also characterized by a flagellar rotation and a proximodistal fusion of the flagellum with the cytoplasmic extension. The most interesting features observed in W virilis are the presence of a reduced, very narrow intercentriolar body and the unique type of flagellar rotation >90°. Results are compared with those described in two caryophyllideans, Glaridacris catostomi Cooper, 1920 and Khawia armeniaca (Cholodkovski, 1915). Contrary to the original report of Świderski and Mackiewicz (2002), that flagellar rotation has never been observed in spermiogenesis of G. catostomi , re-assessment of their description and illustrations leads us to conclude that flagellar rotation must logically occur in that species. The value of various morphological features of sperm in phylogenetic inference is discussed.

During vitellogenesis in Parachristianella trygonis Trypanorhyncha, Eutetrarhynchidae) we distinguished four stages: (1) gonial or stem cell stage; (2) early differentiation stage concentrated on protein synthetic activity and shell-globule formation; (3) advanced differentiation stage with main cell activity concentrated on carbohydrate synthesis (glycogenesis) and massive glycogen storage in the form of α-glycogen rosettes and β-glycogen particles; and finally (4) mature vitellocyte stage. Early vitellocyte maturation is characterised by: (1) an increase in cell volume; (2) extensive development of large, parallel cisternae of GER that produce proteinaceous granules; (3) development of Golgi complexes engaged in packaging this material; (4) continuous enlargement of proteinaceous granules within vacuoles and their transformation into shell-globule clusters composed of heterogeneous material. Cytochemical staining with periodic acid-thiosemicarbazide-silver proteinate for polysaccharides indicated a strongly positive reaction for the presence of α-glycogen rosettes and β-glycogen particles in the advanced stage of vitellocyte maturation. Both protein synthesis for shell-globule formation and carbohydrate synthesis or glycogenesis, important storage of nutritive reserves for the developing embryos, observed during cytodifferentiation of P. trygonis vitellocytes overlap in time to some extent. Mature vitelline cells are very rich in three types of cell inclusions accumulated in large amounts in their cytoplasm: (1) shell-globule clusters, playing an important role in egg-shell formation; (2) numerous large lipid droplets, as well as a high accumulation of lipid and α-glycogen rosettes and β-glycogen particles that undoubtedly represent important nutritive reserves for the developing embryos. Despite the fact that the type of vitellogenesis and ultrastructure of the mature vitellocyte in P. trygonis appears to differ to some extent from those of three other trypanorhynch species, its general pattern and ultrastructure greatly resembles those observed in other lower cestodes. Factors that may have contributed to the qualitative and quantitative variation in lipids during vitellogenesis among the four species of Trypanorhyncha, are identified and discussed.