Spermiogenesis produces the spermatozoa with 9 + '1' and 9 + 0 axonemal pattern in progenetic cestode Diplocotyle olrikii Krabbe, 1874 (Spathebothriidea: Acrobothriidae).

Spermiogenesis in the progenetic spathebothriidean cestode Diplocotyle olrikii has been examined using transmission electron microscopy (TEM) for the first time. Along with the typical features of spermatozoon cytodifferentiation (e.g., the electron-dense material in the apical region of the differentiation zone in the early stage of spermiogenesis, the intercentriolar body which is composed of three electron-dense plates and two electron-lucent zones, the orthogonal development of the two flagella, a flagellar rotation, proximo-distal fusion, the presence of two pairs of electron-dense attachment zones), new for the Eucestoda is detection of the formation of two types of free flagella during spermiogenesis in progenetic D. olrikii, exhibiting either standard 9 + '1' trepaxonematan pattern, or atypical 9 + 0 structure. Various combinations of these two types of flagella resulted in the production of three types of male gametes during spermiogenesis in this spathebothriidean cestode. The first type is represented with the two axonemes of the 9 + '1' structure; the second type exhibits two different axonemes, i.e., one with 9 + '1' and the other of 9 + 0 pattern; and the third type has two axonemes with atypical 9 + 0 structure. The occurrence of three sperm types in progenetic D. olrikii is associated with typical spermiogenesis and has never been described previously in the Platyhelminthes. We suppose that heteromorphism of male gametes in D. olrikii might be linked to progenesis, i.e., the programmed sexual maturation detected during the larval/developmental stage of an organism.

Interrelationships of vitelline and muscle cells within the vitelline follicles of the blood fluke Aporocotyle simplex (Digenea, Aporocotylidae) and morphological evidence for the modification of vitelline material for eggshell formation.

This study of the fish blood fluke Aporocotyle simplex represents the first detailed transmission electron microscopical (TEM) investigation of the vitellarium of an aporocotylid digenean blood fluke. It revealed some unusual characteristics in the cytoarchitecture of the vitelline follicles and demonstrated modifications of the vitelline granules for eggshell formation. The vitelline follicles consist of vitellocytes at different developmental stages surrounded by sarcoplasmic processes of myocytes which occur throughout each follicle. Sites of intimate contact occur between the vitellocytes and the myocytes. Individual vitelline globules (0.1-0.2 µm in diameter) accumulate in quite small clusters of 10-20 and have a dense, heterogeneous matrix possessing central and peripheral regions with a greater density. Modifications of the vitelline globules take place within the clusters and are first apparent when the vitellocytes reach the lumen of the vitelline duct and vitelline reservoir. Globules within the clusters become confluent, and, when the vitellocytes reach the lumen of the oviduct and proximal ootype, these consolidated clusters contain a shapeless, loosely packed, dense material which is released from the vitellocytes by exocytosis. This investigation has provided morphological evidence for shell formation from modified vitelline globules in the form of a discontinuous, thin layer (~ 0.07 µm in thickness) of electron-dense shell material around the fertilized ovum and associated vitellocytes in the proximal ootype. The eggshell of intra-uterine eggs acquires an additional thin, heterogeneous outer layer, increasing its thickness to ~ 0.1 µm. The cytoarchitecture of the vitellarium, modifications of the vitelline globules within the clusters and the structure of the eggshell of A. simplex may prove to be of value in studies examining relationships between the three distinct lineages of aporocotylid digeneans.

Heteromorphism of sperm axonemes in a parasitic flatworm, progenetic Diplocotyle olrikii Krabbe, 1874 (Cestoda, Spathebothriidea).

The spermatozoon ultrastructure of the progenetic cestode Diplocotyle olrikii (Spathebothriidea) has been examined using transmission electron microscopy and cytochemical staining with periodic acid-thiosemicarbazide-silver proteinate (PA-TSC-SP) for glycogen. The spermatozoon is a filiform cell, tapered at both extremities. Its moderately electron-dense cytoplasm possesses two parallel axonemes of unequal lengths. New for the Cestoda is a finding of three types of the mature spermatozoa with respect to different axonemal structure. The first type has both axonemes with standard 9 + '1' trepaxonematan pattern. The second type is represented by a spermatozoon having one axoneme with 9 + '1' structure and the second one with 9 + 0 pattern. The third type includes the two axonemes with 9 + 0 pattern. Microtubule doublets of the 9 + 0 axonemes contain either inner dynein arms or no dynein arms. In addition to the two axonemes, all three types of the mature sperm cells contain parallel nucleus, parallel cortical microtubules, four electron-dense plaques/attachment zones, and glycogen. The anterior extremity of the gamete exhibits a centriole surrounded by a semiarc of up to five electron-dense tubular structures. The distal end of the first type spermatozoa exhibits two morphological variants, represented either by (i) nucleus or (ii) remnants of the disorganized axoneme. Distal extremity of the spermatozoa of the second and third types contains doublets and singlets of disorganized axoneme. The ultrastructural characters of the spermatozoon of progenetic D. olrikii support the basal position of the Spathebothriidea within the Eucestoda.

New data on spermiogenesis and trepaxonematan axoneme in basal tapeworms (Cestoda, Caryophyllidea, Lytocestidae) parasitizing cyprinid fishes.

Monozoic caryophyllidean cestodes, intestinal parasites of cyprinid fishes, represent a group of tapeworms with an unclear evolutionary history. As spermatology may provide phylogenetically important data, the spermiogenesis and ultrastructure of the mature spermatozoon have been investigated using an integrative approach combining transmission electron microscopy, cytochemistry and electron tomography in Khawia rossittensis (Szidat, 1937). The process of spermatid formation is accompanied by the presence of ultrastructural characters not described in traditional models of spermiogenesis, e.g., apical electron-dense material, the two striated roots situated unusually opposite each other, branching of typical striated roots, an intercentriolar body comprising five electron-dense and four electron-lucent layers, rotation of both free flagella and flagellar buds to the median cytoplasmic process at 90°, and a complete proximodistal fusion. The synchronous rotation of both flagellar buds and growing free flagella is an evolutionarily linked pattern favouring the hypothesis that the Caryophyllidea are not ancestral but are secondarily derived from polyzoic forms. Electron tomography analysis has revealed a unique feature of two helicoidal tubular structures in the central electron-dense core of the axoneme of mature spermatozoon. These data provide new insights into the architecture of the 9 + '1' axoneme, which is shared by male gametes of all trepaxonematan Platyhelminthes.

First ultrastructural and cytochemical data on the spermatozoon and its differentiation in progenetic and adult Archigetes sieboldi Leuckart, 1878 (Cestoda, Caryophyllidea, Caryophyllaeidae).

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.

Ultrastructural, cytochemistry and electron tomography analysis of Caryophyllaeides fennica (Schneider, 1902) (Cestoda: Lytocestidae) reveals novel spermatology characteristics in the Eucestoda.

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.

Ultrastructural characteristics of the male ducts and terminal genitalia of an endoparasitic monogenean, Calicotyle affinis Scott, 1911 (Monopisthocotylea: Monocotylidae), with the first detailed description of a copulatory stylet in a monogenean.

This investigation of Calicotyle affinis is the first ultrastructural description of the male reproductive system of a monocotylid monogenean. It has revealed numerous characteristics which are either new or clarify those determined from previous light microscopical observations on the morphology of Calicotyle spp. These include numerous individual testes, each surrounded by its own basal lamina; an ejaculatory bulb delimited by a basal lamina surrounded by two independent internal and external bands of muscles; a bipartite, but not fully divided, muscular chamber (an internal seminal vesicle) in the proximal region of the ejaculatory bulb; well-developed unicellular prostatic glands localised outside the ejaculatory bulb, the cytoplasmic extensions of which pass into the ejaculatory bulb, to form the ducts which open into the lumen of ejaculatory duct; and a male copulatory organ in the form of a coiled penis tube containing throughout its lumen a long, hollow stylet. The penis tube appears to be a modified prolongation of the ejaculatory duct and is supported by a basal lamina and muscle layers. The stylet wall consists of a homogenous, dense material with a narrow, denser inner lining; it is funnel-shaped proximally but narrows imperceptibly towards the distal end of the penis tube, and appears to be a derivative of the basal laminae of the ejaculatory bulb and distal ejaculatory duct. A comparative analysis of the nature of the stylet in relation to those found in free-living platyhelminths forms part of a search for characters useful for understanding monocotylid origins and relationships.

Spermatological characteristics of the enigmatic monogenean Dictyocotyle coeliaca Nybelin, 1941 (Monopisthocotylea: Monocotylidae) reveal possible adaptation to endoparasitism.

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.

Nippotaenia mogurndae Yamaguti et Myiata, 1940 (Cestoda, Nippotaeniidea): first data on spermiogenesis and sperm ultrastructure.

Spermiogenesis and the spermatozoon ultrastructure of the cestode Nippotaenia mogurndae Yamaguti et Myiata, 1940 (Nippotaeniidea), a parasite of Perccottus glenii Dubowski, 1877 (Perciformes: Odontobutidae), have been investigated by means of transmission electron microscopy, cytochemical staining with periodic acid-thiosemicarbazide-silver proteinate (PA-TSC-SP) for glycogen, and electron tomography. The process of spermatozoon formation is characterised by the presence of (1) two centrioles without typical striated rootlets, (2) a single intercentriolar body, (3) a flagellar rotation (free flagellum plus flagellar bud), and (4) a complete proximodistal fusion. The mature spermatozoon of N. mogurndae contains a single helicoidal crested body, one axoneme of the 9 + "1" trepaxonematan structure, parallel cortical microtubules arranged in a ring in the anterior region of the cell, and a spiraled nucleus encircling the axoneme. Intracellular components are situated in a moderately electron-dense cytoplasm, containing glycogen in the principal regions (II, III, IV) of the spermatozoon. Application of electron tomography has revealed a helicoidal nature of the central electron-dense core in the central cylinder of the axoneme in parasitic cestodes for the first time. The patterns of spermiogenesis and spermatozoon ultrastructure resemble most closely those in mesocestoidids and may reflect the relationships between Nippotaeniidea and Mesocestoididae.

Vitellogenesis of diphyllobothriidean cestodes (Platyhelminthes).

The recently erected cestode order Diphyllobothriidea is unique among all tapeworm orders in that its species infect all major groups of tetrapods, including man. In the present paper, the vitellogenesis of representatives of all three currently recognized families of this order was evaluated, based on ultrastructural (transmission electron microscopy) and cytochemical (detection of glycogen) observations. Vitelline follicles of all taxa studied, i.e. Cephalochlamys namaquensis from clawed frogs (Xenopus), Duthiersia expansa from monitors (Varanus) and Schistocephalus solidus that matures in fish-eating birds, contain vitelline cells at various stages of development and interstitial cells. Developing vitellocytes are characterized by the presence of mitochondria, granular endoplasmic reticulum and Golgi complexes involved in the synthesis of shell globules and formation of shell globule clusters. Mature vitellocytes contain lipids and glycogen in different proportions. The most significant differences among the three diphyllobothriidean families were found in the presence or absence of lamellar bodies. Variations of vitelline clusters morphology and types of lipid droplets are described and discussed in relation to the presumed evolutionary history of diphyllobothriideans, which belong to the most basal cestode groups.

Ultrastructural features of the spermatozoon and its differentiation in Brandesia turgida (Brandes, 1888) (Digenea, Microphalloidea, Pleurogenidae).

Spermatological characters of the digenean Brandesia turgida (Brandes, 1888), an intestinal parasite of the frog Pelophylax ridibundus (Pallas, 1771), have been investigated by means of transmission electron microscopy for the first time. The process of the spermatozoon formation begins with the appearance of the differentiation zone bordered by cortical microtubules and containing two centrioles associated with striated rootlets and with an intercentriolar body. The intercentriolar body is made up of seven distinct electron-dense plates, two less electron-dense, and four electron-lucent zones. The orthogonal development of the two flagella is followed by a flagellar rotation and their proximodistal fusion with the median cytoplasmic process. This process is accompanied by an extension of both the mitochondrion and nucleus into the median cytoplasmic process. The mature spermatozoon of B. turgida contains two parallel axonemes of unequal lengths with the 9 + "1" trepaxonematan pattern, mitochondrion, nucleus, parallel cortical microtubules, four electron-dense attachment zones, an external ornamentation of the plasma membrane, and electron-dense glycogen granules. The anterior extremity of the male gamete contains one complete centriole, a small component of the central element of the second centriole, and peripheral cortical microtubules (up to 45). The posterior extremity of the mature spematozoon exhibits tubular elements of the disorganized axoneme. The present study provides the first data on spermiogenesis within the family Pleurogenidae. Variations of the spermatozoa ultrastructural characters within Digenea, in particular, between different families of the superfamily Microphalloidea, are discussed.

Cytocomposition of the vitellarium in Khawia sinensis Hsü, 1935 (Cestoda, Caryophyllidea, Lytocestidae): another caryophyllidean species with lamellar bodies and lipids.

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.

A reinvestigation of spermiogenesis in Amphilina foliacea (Platyhelminthes: Amphilinidea).

Spermiogenesis in the amphilinidean cestode Amphilina foliacea (Rudolphi, 1819) was examined using transmission electron microscopy. The orthogonal development of the two flagella is followed by a flagellar rotation and their proximodistal fusion with the median cytoplasmic process. This process is accompanied by extension of both the mitochondrion and nucleus into the median cytoplasmic process. The two pairs of electron-dense attachment zones mark the lines where the proximodistal fusion of the median cytoplasmic process with the two flagella takes place. The intercentriolar body, previously undetermined in A.foliacea, is composed of three electron-dense and two electron-lucent plates. Also new for this species is the finding of electron-dense material in the apical region of the differentiation zone at the early stage of spermiogenesis, and the fact that two arching membranes appear at the base of the differentiation zone only when the two flagella rotate towards the median cytoplasmic process. The present data add more evidence for a close relationship between the Amphilinidea and the Eucestoda.

Ultrastructure of the vitellarium of Ancyrocephalus paradoxus (Monogenea: Monopisthocotylea), with comments on the nature of the vitellarium in the Monogenea and related platyhelminth groups.

Fine structural features of the vitelline follicles of the monopisthocotylean monogenean Ancyrocephalus paradoxus are revealed and compared with those of other monogenean species. As in other monogeneans, each vitelline follicle of A. paradoxus is composed of a single cell type, i.e. vitellocytes at various stages of development, with no sign of any interstitial cells. There is no special isolation of the vitelline follicles from the surrounding tissue, and both heterologous (between adjacent membranes of the vitelline and surrounding parenchymal cells) and homologous (between adjacent membranes of the vitelline cells) cell junctions (zonulae occludentes) are present. Non-membrane-bound vitelline clusters of A. paradoxus contain 50-100 vitelline globules, moderately electron-dense lipid droplets and glycogen particles present in the mature cell cytoplasm. In a search for phylogenetically informative characters of the fine structure of the vitellarium, the new findings are compared with those known for trematodes, and, to enable this, additional observations were made on the structure of the vitellarium of the aspidogastrean Aspidogaster limacoides. Some new discriminatory traits are revealed in A. limacoides; these include the presence of a single type of cellular component within the vitellarium, sarcoplasmic processes filling the space between and around the vitellocytes and zonulae occludentes between adjacent membranes of vitelline and muscle cells. On the basis of ultrastructural features of the vitellarium, a relationship between the Monogenea and the Aspidogastrea is indicated.

Ultrastructure of the vitellarium in the digeneans Phyllodistomum angulatum (Plagiorchiida, Gorgoderidae) and Azygia lucii (Strigeida, Azygiidae).

Fine structural features of the vitellarium of two digeneans, Phyllodistomum angulatum and Azygia lucii, are documented and compared with those of other digenean species. The cytodifferentiation of immature vitelline cells (vitellocytes) assumes the production and subsequent accumulation in their cytoplasm of several inclusions. Mature vitelline cells of P. angulatum are characterized by the presence of vitelline clusters (∼2.7 µm in diameter, with ∼100 vitelline globules of ∼0.35 µm in diameter) and osmiophobic, saturated lipid droplets (∼2-3 µm in diameter), and in A. lucii vitelline clusters of the same diameter include much fewer vitelline globules (∼50 globules of ∼0.5 µm in diameter), osmiophilic lipid droplets and α-glycogen. In both P. angulatum and A. lucii, interstitial cells are also present within the vitellarium. Two types of contact sites (septate and tight junctions) between adjoining interstitial cells also occur in both digenean species. Judging from the present and previous ultrastructural studies, it is suggested that there are three potential discriminatory characters of the digenean vitellarium (the number of different types of cell components within the vitellarium, the presence and type of junctional complexes between these cells, and the isolation of the vitellarium from the surrounding tissue) which may prove useful for a better understanding of the biology and evolutionary history of the different digenean groups.

Spermatozoon cytoarchitecture of Amphilina foliacea (Platyhelminthes, Amphilinidea).

The mature spermatozoon of Amphilina foliacea Rudolphi, 1819 has been examined using transmission electron microscopy. The male gamete is filiform and tapered at both extremities. Its moderately electron-dense cytoplasm possesses two parallel axonemes of unequal lengths with the 9 + "1" trepaxonematan pattern, a mitochondrion, a nucleus, parallel cortical microtubules, four electron-dense attachment zones, and electron-dense glycogen granules. A crested body is absent. The anterior extremity of the cell exhibits a single axoneme. The anteriormost cortical microtubules have been observed with the appearance of the second axoneme. The number of cortical microtubules reaches a maximum (up to 25) in the nucleated region III of the spermatozoon. A single mitochondrion extends from the middle of region II to the end of region III of the cell. Both axonemes have become disorganized in a similar way: the axonemal doublets disappear first, followed by the central core. The nucleus is surrounded by a few cortical microtubules in the proximal part of region V. In the distal extremity of the mature spermatozoon, there is only the nucleus. Differences of spermatozoon ultrastructure within Amphilinidea and other Neodermata are discussed.

Ultrastructure of the spermatozoon of the diphyllobothriidean cestode Cephalochlamys namaquensis (Cohn, 1906).

This contribution provides the first ultrastructural and cytochemical data on the mature spermatozoon of a diphyllobothriidean cestode belonging to the family Cephalochlamydidae. The mature spermatozoon of Cephalochlamys namaquensis (Cohn, 1906), a parasite of the African clawed frog, Xenopus laevis (Daudin, 1802), from southern California, USA, has been examined using transmission electron microscopy and cytochemical staining with periodic acid-thiosemicarbazide-silver proteinate for glycogen. The male gamete is a filiform cell tapered at both extremities. Its moderately electron-dense cytoplasm possesses two parallel axonemes of unequal lengths with a 9 + "1" trepaxonematan pattern, a nucleus, parallel cortical microtubules, four electron-dense plaques/attachment zones, and electron-dense granules of glycogen. The crested body is absent. The anterior extremity of the cell exhibits a centriole surrounded by a semiarc of four parallel cortical microtubules. The number of cortical microtubules reaches its maximum (up to 37) at the beginning of the anucleated two-axoneme region II of the spermatozoon. In contrast to other diphyllobothriideans, a small membranous element appears in the anucleated region II. In addition, the nucleus is surrounded by a few cortical microtubules in region V. The distal extremity of the mature spermatozoon exhibits only one nucleus. Variations of spermatozoa ultrastructural characters within diphyllobothriideans as well as other Eucestoda are discussed.

Revisiting caryophyllidean type of spermiogenesis in the Eucestoda based on spermatozoon differentiation and ultrastructure of Caryophyllaeus laticeps (Pallas, 1781).

Spermiogenesis of the monozoic cestode Caryophyllaeus laticeps (Pallas, 1781) (Caryophyllidea: Caryophyllaeidae), a parasite of Abramis brama (Pisces: Cyprinidae), has been investigated by means of transmission electron microscopy and cytochemical staining with periodic acid-thiosemicarbazide-silver proteinate for glycogen. The process of spermatozoon formation corresponds in the basic pattern to that of Khawia armeniaca as described by Brunanská and Poddubnaya (Parasitol Res 99:449-454, 2006). The dense material at the early stages of spermiogenesis, an intercentriolar body, the formation of a free flagellum and flagellar bud, the penetration of the nucleus into the spermatid body when the fusion of the free flagellum with the median cytoplasmic process has started, and a complete proximodistal fusion have been determined. In contrast to previous data on the caryophyllidean type spermiogenesis, the latter more recent observations show the presence and the rotation of a free flagellum and a flagellar bud. This pattern indicates clearly a derived stage of spermiogenesis in the Caryophyllidea, when the second shorter flagellum is greatly reduced comparing with that in the Spathebothriidea, Diphyllobothriidea, or Bothriocephalidea, thus forming a flagellar bud. The flagellar bud occurs in all stages of spermiogenesis and represents an evolved character in the Caryophyllidea. The mature spermatozoon of C. laticeps consists of one axoneme of the 9 + "1" trepaxonematan structure, parallel cortical microtubules, and a nucleus. Cell components are situated in a moderately electrondense cytoplasm, containing glycogen in the principal regions (II, III, and IV) of the spermatozoon. A crested body is absent. Similarities and differences between spermatozoa of caryophyllideans as well as other Eucestoda are discussed.

Early intrauterine embryonic development in Khawia sinensis Hsü, 1935 (Cestoda, Caryophyllidea, Lytocestidae), an invasive tapeworm of carp (Cyprinus carpio): an ultrastructural study.

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.

Ultrastructural aspects of spermatogenesis, testes, and vas deferens in the parthenogenetic tapeworm Atractolytocestus huronensis Anthony, 1958 (Cestoda: Caryophyllidea), a carp parasite from Slovakia.

Spermatogenesis, testes, and vas deferens in the parthenogenetic monozoic tapeworm Atractolytocestus huronensis Anthony, 1958 (Cestoda: Caryophyllidea) from Slovakia, parasitizing the carp Cyprinus carpio L., have been investigated by means of transmission electron microscopy for the first time. The present results show that helminths with parthenogenetic and normal reproduction may share some common spermatology features, e.g., dense cytoplasm of the peripherally localized spermatogonia or a rosette type of spermatogenesis. In contrast to tapeworms with normal reproduction, the most prominent ultrastructural characteristic of the spermatocytes of A. huronensis is fragmentation of their nuclei. This clear feature of cell degeneration might be a consequence of the aberrant first meiotic division. Peripheral cortical microtubules and a single centriole, indicators of the ongoing spermiogenesis, were observed only very rarely in the early spermatids. Characteristics of normal spermiogenesis, i.e., apical dense material in the zone of differentiation in early stages of spermiogenesis, flagellar rotation, and proximo-distal fusion, were never found in the present study. The testes follicles are surrounded by a thin cytoplasmic sheath underlined by a basal lamina. Vas deferens is lined by flat epithelium with numerous surface lamellae and cilia. Mature, functional spermatozoa were not observed in the vas deferens of A. huronensis from Slovakia.