Ultrastructure and cytochemistry of the tegument of Atriaster heterodus (Platyhelminthes: Monogenea)

The tegument of the polyopisthocotylean monogenean Atriaster heterodus Lebedev & Parukhin, 1969 was studied using transmission electron microscopy. The outer syncytial layer of the tegument is connected to the internal cell bodies by cytoplasmic extensions which interweave between the muscular fibres. The free surface of the syncytium has projections of the external membrane which are similar to microvilli. The undulating basal membrane, with numerous narrow elongate projections, is associated with the basal lamina situated between the syncytial and muscular layers. The cell bodies and syncytial layer of the tegument exhibit two types of vesicles, one with fibrous contents and one with electron-dense contents; these were analysed using two cytochemical tests, the E-PTA and alcian blue methods, used for the first time on monogeneans.     

Phylogenetic relationships between the families Capsalidae and Dionchidae (Platyhelminthes, Monogenea, Monopisthocotylea) indicated by the comparative ultrastructural study of spermiogenesis

Comparative ultrastructural observations were carried out on the spermiogenesis of the capsalid Caballerocotyla manteri Price and the dionchid Dionchus remorae MacCallum. At the beginning of spermiogenesis the zones of differentiation (ZD) jut out in all directions. A large mitochondrion shaped like a perforated bead, and through which the elongated nucleus passes, is found facing each ZD. Later the ZD become parallel and are embedded within the common cytoplasmic mass. Cortical longitudinal microtubules are present in the ZD at the outset of spermiogenesis, but they later disappear. The spermatozoon is long and filiform. It shows two parallel axonemes of the 9 +"1" flatworm pattern, the nucleus and mitochondrion, and no cortical microtubule. The ultrastructure of spermiogenesis and spermatozoon is remarkably similar in the two species studied, as in other capsalids previously described. Two characteristics, the perforated bead shape of the spermatid mitochondrion and the progressive disappearance of the microtubules of the ZD, may be considered as synapomorphies which indicate close phylogenetic relationships between the families Dionchidae and Capsalidae. This interpretation coincides with Llewellyn's (1971) scheme of the evolution of the monogeneans.     

The aflagellate spermatozoon of Diplozoon (Platyhelminthes: Monogenea: Polyopisthocotylea): a demonstrative case of relationship between sperm ultrastructure and biology of reproduction

Diplozoon is known to display an exceptional biology of reproduction: the hermaphroditic adults are permanently fused together and their genital ducts communicate. In contrast to all other polyopisthocotylean monogeneans in which the spermatozoa show an homogeneous biflagellate structure, the spermatozoon of Diplozoon is aflagellate. It is filiform, and composed of a cytoplasmic region and a nuclear region. The cytoplasmic region exhibits mitochondria, a well-developed smooth endoplasmic reticulum, and up to 450 longitudinal singlet microtubules. The microtubules show links between them; seen in cross section, they are arranged as rows or polygons. The spermatozoon nuclear region contains the nucleus surrounded by cortical longitudinal microtubules. The spermiogenesis shows no zone of differentiation, a typical structure found in all other parasitic Platyhelminthes. Diplozoon is the first case of aflagellate spermatozoon found in the parasitic Platyhelminthes. The atypical sperm structure is not linked with phylogeny, but is well correlated with the atypical biology of reproduction.     

Studies on Fertilization in Glycine max

This work studies the whole process of fertilization in Glycine max. The results are summarized as follows: 1. The type of ripened pollen grain of soybean was two-cell type. The generative cell was divided mitotically into two spermatids within the pollen tube. 2. In the 6th hour after self-pollination, the pollen tube entered into the embryo sac and released two sperms. Before the fusion of the male and female nuclei, the cytoplasmic sheath of the spermatids falled off. The cytoplasm of the male gamete did not fuse with that of the egg cell. 3. In the 6th hour after self-pollination, one spermatid nucleus come in contact with the egg nucleus and the other with the secondary nucleus, The contact of the sperimatid nucleus with the egg nucleus was a little earlier than that with the secondary nucleus. 4. The spermatid nucleus entered into the egg nucleus; the chromatic granules of the spermatid despiralized. After the complete fusion of the spermatid nucleus with the egg nucleus, the egg nucleus was darkly stained and the chromonemata increased, afterward the male nucleus appeared. 5. In the 28th hour after self-pollination, the zygote begun the first mitotic division. It took about 20 hours to fuse the male and female gametes, and to form the zygote untile before first mitotic division. It means that the zygote dormancy stage of soybean was about twenty hours. 6. In the 7th hour after self-pollination, the spermatid nucleus fused with the secondary nucleus. The process was similar to that of the spermatid nucleus with the egg nucleus. The chromatic granules gradually despiralized within the secondary nucleus, and the male nucleoli appeared. The velocity of the fusion of the spermatid nucleus with the secondary nucleus was faster than that of the other spermatid nucleus with the egg nucleus. 7. In the 10th hour after self-pollination, the secondary nucleus begun the first mitotic division. 8. The fertilization of soybean was the premitotic type.     

Intercellular organelle traffic through cytoplasmic bridges in early spermatids of the rat: mechanisms of haploid gene product sharing

Stable cytoplasmic bridges (or ring canals) connecting the clone of spermatids are assumed to facilitate the sharing of haploid gene products and synchronous development of the cells. We have visualized these cytoplasmic bridges under phase-contrast optics and recorded the sharing of cytoplasmic material between the spermatids by a digital time-lapse imaging system ex vivo. A multitude of small (ca. 0.5 microm) granules were seen to move continuously over the bridges, but only 28% of those entering the bridge were actually transported into other cell. The average speed of the granules decreased significantly during the passage. Immunocytochemistry revealed that some of the shared granules contained haploid cell-specific gene product TRA54. We also demonstrate the novel function for the Golgi complex in acrosome system formation by showing that TRA54 is processed in Golgi complex and is transported into acrosome system of neighboring spermatid. In addition, we propose an intercellular transport function for the male germ cell-specific organelle chromatoid body. This mRNA containing organelle, ca. 1.8 microm in diameter, was demonstrated to go over the cytoplasmic bridge from one spermatid to another. Microtubule inhibitors prevented all organelle movements through the bridges and caused a disintegration of the chromatoid body. This is the first direct demonstration of an organelle traffic through cytoplasmic bridges in mammalian spermatogenesis. Golgi-derived haploid gene products are shared between spermatids, and an active involvement of the chromatoid body in intercellular material transport between round spermatids is proposed.     

Spermiogenesis in a Scutariellid (Platyhelminthes)

Spermiogenesis and spermatozoa were studied by transmission and scanning electron microscopy in Troglocaridicolasp., a scutariellid epizoic on a cavernicolous freshwater shrimp. Spermiogenesis involves elongation of the spermatid in which the nucleus elongates, but remains close to the common cytoplasmic mass. Flagella first grow in opposite direction and at a right angle to the cytoplasmic shaft, and centrioles show associate structures. Later, the two centrioles rotate and the flagella emerge parallel, but still perpendicular to the shaft. An apical process elongates at the extremity of the spermatid shaft. The spermatozoon shows active flagellar beating and undulations of the sperm body. The spermatozoon comprises an anterior ‘corkscrew’ region, the flagellar insertion region, a cytoplasmic region and a posterior nuclear region. The corkscrew contains an electron dense structure, not membrane-bound, originating from the apical process of the spermatid. The flagella show the 9+‘1’ pattern, usual in Platyhelminthes. The cytoplasmic and nuclear regions show a cortical row of about 50 twisted longitudinal microtubules surrounding a row of electron dense, and not membrane-bound, 25-nm granules. These granules are original structures and seem to be known only in a few Platyhelminthes species in which a non-flagellar movement of the spermatozoon occurs. Thus, it is hypothesised that the 25-nm granules play a role in cellular motility. Sperm ultrastructure in Troglocaridicolashows major differences to that in the temnocephalids. It is therefore concluded that the phylogenetic position of the scutariellids within the Temnocephalidea should be reinvestigated.     

Toxoplasma gondii and mast cell interactions in vivo and in vitro: experimental infection approaches in Calomys callosus (Rodentia, Cricetidae)

In the present work, we studied some qualitative and quantitative characteristics of mast cells located in the peritoneal cavity, submandibular and dorsal lymph nodes and ileum of Calomys callosus experimentally infected by Toxoplasma gondii. In uninfected animals, the majority of mast cells had similar ultra-structural characteristics, including several cytoplasmic granules with homogeneous and electron dense contents. However, after 1 h of infection, a significant influx of mast cells into peritoneal cavity was observed. The number of mast cells in this compartment decreased progressively in infected animals, and was significantly lower than the number of mast cells in control animals after 48 h of infection. Mast cells from infected animals or from purified suspensions that were infected in vitro presented significant morphological modifications, suggesting a degranulation process: cytoplasmic granules with electron dense content, fusion of the cytoplasmic granules, intracytoplasmic channels, cytoplasmic granules with flocculent material, plasma membrane rupture and granule contents in the extracellular environment. A remarkable increase in the influx of neutrophils toward the peritoneal cavity of the infected animals was observed after 12 h of infection. Moreover, this event occurred after the mast cell degranulation process took place. The relative increase in the number of mast cells and neutrophils was also followed by an increase in the number of macrophages, but there was a significant decrease in lymphocyte influx. After 48 h of infection, the parasite had spread from the peritoneal cavity to all organs examined. Also, mast cells from these organs showed evident morphological alterations, indicating the presence of the degranulation process. These results suggest that mast cells are deeply involved with the acute phase of the inflammatory response in this experimental model.     

Ultrastructural study of spermiogenesis and the spermatozoon of the proteocephalidean cestode Barsonella lafoni de Chambrier et al., 2009, a parasite of the catfish Clarias gariepinus (Burchell, 1822) (Siluriformes, Clariidae)

Spermiogenesis in the proteocephalidean cestode Barsonella lafoni de Chambrier et al., 2009 shows typical characteristics of the type I spermiogenesis. These include the formation of distal cytoplasmic protrusions forming the differentiation zones, lined by cortical microtubules and containing two centrioles. An electron-dense material is present in the apical region of the differentiation zone during the early stages of spermiogenesis. Each centriole is associated to a striated rootlet, being separated by an intercentriolar body. Two free and unequal flagella originate from the centrioles and develop on the lateral sides of the differentiation zone. A median cytoplasmic process is formed between the flagella. Later these flagella rotate, become parallel to the median cytoplasmic process and finally fuse proximodistally with the latter. It is interesting to note that both flagellar growth and rotation are asynchronous. Later, the nucleus enlarges and penetrates into the spermatid body. Finally, the ring of arching membranes is strangled and the young spermatozoon is detached from the residual cytoplasm.The mature spermatozoon presents two axonemes of the 9 + ‘1’ trepaxonematan pattern, crested body, parallel nucleus and cortical microtubules, and glycogen granules. Thus, it corresponds to the type II spermatozoon, described in almost all Proteocephalidea. The anterior extremity of the gamete is characterized by the presence of an apical cone surrounded by the lateral projections of the crested body. An arc formed by some thick and parallel cortical microtubules appears at the level of the centriole. They surround the centriole and later the first axoneme. This arc of electron-dense microtubules disorganizes when the second axoneme appears, and then two parallel rows of thin cortical microtubules are observed. The posterior extremity of the male gamete exhibits some cortical microtubules. This type of posterior extremity has never been described in proteocephalidean cestodes. The ultrastructural features of the spermatozoon/spermiogenesis of the Proteocephalidea species are analyzed and compared.     

Spermiogenesis in Paratomella rubra(Platyhelminthes, Acoela): Ultrastructural, Immunocytochemical, Cytochemical Studies and Phylogenetic Implications

Spermiogenesis and sperm structure of the primitive acoel Paratomella rubra from the Ligurian Sea, Italy, were investigated by several methods. During spermiogenesis, after flagellar incorporation by formation of two longitudinal lateral grooves, spermatid elongation is characterized in Paratomella by the presence of four membranes encircling each axoneme plus two membranes encircling both the axonemes and the nucleus. These structures were interpreted as being three cytoplasmic canals situated one inside the other. The filiform spermatozoon has two incorporated axonemes of 9+2 type, a nucleus almost as long as the sperm cell itself, a single elongate mitochondrion, and two types of membrane-bound granules, respectively, small and gastrula-shaped, and large. Organelles are highly ordered, the sperm is bilaterally symmetrical with a single long mitochondrion on the ventral side and a regular row of large granules, for some length embedded in the nucleus, on the dorsal side. Immunocytochemical studies and the use of fluorescent nuclear dyes reveal the spatial relationships of the axonemes with the nucleus. The granules were shown by Thiéry, PTA and enzyme digestion tests to contain glycoproteins and/or polysaccharides and very little protein. Glycogen particles were detected in the cytoplasm. Cells containing coiled spermatozoa undergoing resorption were found in the parenchyma. New apomorphies of the taxon Paratomella based on sperm structure are proposed: a very long nucleus, a highly bilaterally symmetrical pattern of organelles, a single long mitochondrion. These characters are not found in other Acoela, and particularly in Hesiolicium , sometimes considered closely related to Paratomella . © 1997 Published by Elsevier Science Ltd on behalf of The Royal Swedish Academy of Sciences.     

The behaviour of centrioles and the formation of the flagellum in rooster and drake spermatids

Summary Developmental changes in the formation of the centrioles and flagellum during spermiogenesis in the rooster and drake were studied.Changes in the length and thickness of the wall of the centrioles were observed from an early stage of spermatid development. Before the proximal centriole is attached to the nucleus microtubules were observed near the centrioles joined to them. At this stage of spermatid development changes on the nuclear membrane were observed at a place where the proximal centriole is attached to the nucleus. At the later stage of spermatid differentiation three to five dense extensions in the space of the nuclear invagination and dense bodies or granules near the distal centriole were present. The anterior part of the newly formed flagellum is covered by a cytoplasmic membrane displaying extension which is approximately 1.3 m long. Slight differences between the two species were observed.     

Microtubular system during spermiogenesis and in the spermatozoon of Convoluta saliens (platyhelminthes,acoela): Tubulin immunocytochemistry and electron microscopy

Spermiogenesis and the spermatozoon were studied in Convoluta saliens, an acoel platyhelminth, by transmission electron microscopy, labelling of nuclei and immunocytochemistry of tubulin with various antibodies. Spermiogenesis involves formation of a long spermatid shaft containing two axonemes. It is established that the nucleus, after a stage of elongation, does not migrate up to the distal extremity of the spermatid, and that the centriolar derivatives are located at the distal extremity of the shaft. This contrasts with the parasitic Platyhelminthes. The mature spermatozoon, 180 μm in length, comprises a nuclear region, 50 μm in length, and a cytoplasmic region, with a short region of overlap. The cytoplasmic region contains two lateral axonemes with a 9 + 2 pattern of microtubules, granules of two different sizes, and two rows of longitudinal microtubules in the center. Each row consists of 5–6 singlet microtubules, with links between them. Whereas the two axonemes are labelled by antibodies against alpha, acetylated‐alpha, and beta tubulin, the microtubule rows are labelled only by the anti‐beta‐tubulin antibody. This suggests that acetylation does not occur in this part of the cytoskeleton, and that the epitope recognized by the anti‐alpha‐tubulin antibody (DM1A) is different in these units. Mol. Reprod. Dev. 52:74–85, 1999. © 1999 Wiley‐Liss, Inc.     

Dynein light chain 1 regulates dynamin-mediated F-actin assembly during sperm individualization in Drosophila

Toward the end of spermiogenesis, spermatid nuclei are compacted and the clonally related spermatids individualize to become mature and active sperm. Studies in Drosophila showed that caudal end-directed movement of a microfilament-rich structure, called investment cone, expels the cytoplasmic contents of individual spermatids. F-actin dynamics plays an important role in this process. Here we report that the dynein light chain 1 (DLC1) of Drosophila is involved in two separate cellular processes during sperm individualization. It is enriched around spermatid nuclei during postelongation stages and plays an important role in the dynein-dynactin-dependent rostral retention of the nuclei during this period. In addition, DDLC1 colocalizes with dynamin along investment cones and regulates F-actin assembly at this organelle by retaining dynamin along the cones. Interestingly, we found that this process does not require the other subunits of cytoplasmic dynein-dynactin complex. Altogether, these observations suggest that DLC1 could independently regulate multiple cellular functions and established a novel role of this protein in F-actin assembly in Drosophila.     

Putatively luminous tissue in the abdominal pouch of a male dalatiine shark, Euprotomicroides zantedeschia Hulley & Penrith, 1966

The putatively luminous villous tissue in an abdominal pouch of a male specimen of the oceanic midwater shark Euprotomicroides zantedeschia is described. The epithelium within the pouch is probably stratified. The most conspicuous cell type is tall columnar cells, typically containing small cytoplasmic granules and a large inclusion. Cells with similar cytoplasmic characteristics, thought to be photogenic cells, are present in the epidermal skin photophores in other selachians which are known to be luminous.     

Spermatogenesis in a monogenean, Diclidophora merlangi.

Halton D. W. &; Hardcastle A. 1976. Spermatogenesis in a monogenean, Diclidophora merlangi. International Journal for Parasitology6: 43–53. Development of the spermatozoa in the testis of a polyopisthocotylean fish-gill fluke, Diclidophora merlangi, has been examined by light and electron microscopy. Spermatogonial cells are typically undifferentiated and display numerous free ribosomes and relatively little cytoplasm. Successive mitotic divisions produce spermatocytes which are characterized by expansion of the ER and the development of Golgi complexes. Nuclear division is followed by incomplete cytokinesis so that spermatocytes and subsequent stages are joined and develop syncytially. Nuclear synaptonemal complexes mark the first division of the meiotic phase, the second giving rise to a rosette of 32 spermatids. During spermateleosis, the spermatid nucleus condenses and migrates into a conical-shaped projection of cytoplasm. A centriole-like structure and basal bodies, anchored by a pair of attached rootlets, produce axial filaments that grow out from the spermatid and eventually fuse with the nuclear projection. Spermatozoa are then released from the residual cytoplasm. Each spermatozoon is approximately 325 μm in length and 2 μm maximum diameter and in section shows a nucleus, mitochondrion, paired axial units which conform to the “9 +1” pattern described for other platylelminthes, particles of β-glycogen, and a line of micro-tubules around the inner aspect of the limiting membrane.     

Spermiogenesis and spermatozoon ultrastructure of the davaineid cestode Raillietina micracantha (Fuhrmann, 1909)

Miquel, J., Torres, J., Foronda, P. and Feliu, C. 2010. Spermiogenesis and spermatozoon ultrastructure of the davaineid cestode Raillietina micracantha. — Acta Zoologica (Stockholm) 91 : 212–221 The spermiogenesis and the ultrastructural organization of the spermatozoon of the davaineid cestode Raillietina micracantha are described by means of transmission electron microscopy. Spermiogenesis begins with the formation of a zone of differentiation containing two centrioles. One of the centrioles develops a free flagellum that later fuses with a cytoplasmic extension. The nucleus migrates along the spermatid body after the proximodistal fusion of the flagellum and the cytoplasmic extension. During advanced stages of spermiogenesis a periaxonemal sheath and intracytoplasmic walls appear in the spermatids. Spermiogenesis finishes with the appearance of two helicoidal crested bodies at the base of spermatids and, finally, the narrowing of the ring of arched membranes detaches the fully formed spermatozoon. The mature spermatozoon of R. micracantha is a long and filiform cell, tapered at both ends, which lacks mitochondria. It exhibits two crested bodies of different lengths, one axoneme of the 9 + ‘1’ pattern of trepaxonematan Platyhelminthes, twisted cortical microtubules, a periaxonemal sheath, intracytoplasmic walls, granules of glycogen and a spiralled nucleus. The anterior extremity of the spermatozoon is characterized by the presence of an electron‐dense apical cone and two spiralled crested bodies while the posterior extremity of the male gamete exhibits only the axoneme and an electron‐dense posterior tip.     

Spermiogenesis in the cestode Corallobothrium solidum Fritsch, 1886 (Proteocephalidea: Corallobothriinae)

Spermiogenesis of Corallobothrium solidum Fritsch 1886, has been investigated by transmission electron microscopy. The zone of differentiation contains the two centrioles, each with one thin root, being orientated in the same plane only when a single intercentriolar body (ICB) appears between them. A median cytoplasmic process (MCP) develops distally to the two flagella, which are of unequal length, get longer and rotate towards the MCP. The nucleus penetrates into the spermatid body after the fusion of both flagella with the MCP has started. Flagellar roots occur occasionally in some spermatids. New for the Eucestoda are the following findings: 1. cortical microtubules (CMs) are arranged in two short parallel rows in one‐axoneme region of some spermatids; 2. the crested body of spermatid consists either of electron‐dense tubular elements and interposes itself between CMs, or it is rather homogeneous and situated more peripherally above one continuous semicircle of CMs. The present results support previous data that the type of spermiogenesis in proteocephalideans resembles mostly that observed in tetraphyllideans (Onchobothriidae and Phyllobothriidae), thus supporting the view of a close phylogenetic relationship of tetraphyllidean and proteocephalidean cestodes.     

Membranous tubes in pseudoscorpion spermiogenesis

The highly complicated differentiation of the spermatid in the pseudoscorpion Diplotemnus sp. is accomplished without the presence of microtubules. Instead membranous tubes measuring approximately 50 nm in diameter and closely associated with endoplasmic reticulum are found from early to mid spermatids. The lumen of the tube is devoid of electron dense contents but a fluffy material is attached to the cytoplasmic side. They run straight or slightly bent and are in open connection with the cell membrane. First appearing near the cell bridge of the interconnected spermatids they form a bundle in the longitudinal axis during a transitory phase of elongation. When the cell rounds off again the tubules together with the endoplasmic reticulum disappear. The arrangement of the tubes and their presence during abortive elongation of the spermatid suggest a supportive function commonly attributed to microtubules. Moreover, the open connection with the cell membrane and their close association with the endoplasmic reticulum may indicate their participation also in transport.     

Spermiogenesis and sperm in Mesostoma viaregginum (Plathelminthes, Rhabdocoela): an ultrastructural study to infer sperm orientation

Spermiogenesis in Mesostoma viaregginum begins with the formation of a zone of differentiation containing striated rootlets, two centrioles, and an intercentriolar body in-between. These centrioles generate two parallel free-flagella with the 9+“1” pattern of the Trepaxonemata growing out in opposite directions. Spermatid differentiation is characterised by a 90° latero-ventral rotation of flagella and a subsequent disto-proximal centriolar rotation, with a distal cytoplasmic projection. The former rotation involves the compression of a row of cortical microtubules and allows recognising a flagellar side and an aflagellar side in the late spermatid and in the mature spermatozoon. At the end of the differentiation, centrioles and microtubules lie parallel to the spermatid axis. The disto-proximal centriolar rotation is proposed as a synapomorphy for the Rhabdocoela. The modifications of the intercentriolar body during spermiogenesis and the migration of the nucleus and the centrioles towards the cytoplasmic distal projection are also described. The mature spermatozoon of M. viaregginum is filiform and tapered at both ends and presents many features found in the Rhabdocoela gametes. The nucleus disappears before the flagellar insertion and a density gradient of mitochondria is observed along the sperm axis. The anterior end of the spermatozoon of M. viaregginum is characterised by a tapering capped by a membrane expansion. This study has enabled us to describe precisely the orientation of spermatozoa in the Rhabdocoela in general: the centriolar extremity is proposed as the anterior one for the Rhabdocoela.     

Fine structure of the formation and fate of the residual bodies of mouse spermatozoa with evidence for the participation of lysosomes

Routine electron microscopy in combination with subcellular localization of acid phosphatase has been employed to study the formation and fate of residual cytoplasmic bodies extruded into the tubular lumen shortly before spermiation. Prior to extrusion the spermatid cytoplasm contains lipid droplets, mitochondria, ribosomes, endoplasmic reticulum, the caudally migrated Golgi apparatus, and numerous multivesicular and multigranular bodies. These membrane-limited bodies and the Golgi zone stain heavily for acid phosphatase. Following extrusion the residual bodies undergo a series of alterations: (1) disruption of multigranular bodies with release of free granules; (2) sequestration of granules, ribosomes, and reticulum inside double-membrane-limited vacuoles derived from Golgi lamellae; (3) appearance of numerous, single-membrane-bound, cytoplasmic vacuoles; (4) fragmentation; (5) peripheral migration toward the tubular wall; and (6) phagocytosis of these migrating fragments by the Sertoli cells. The demonstration of acid phosphatase activity within free granules, the sequestering Golgi lamellae, and both classes of vacuoles suggests that initial residual body degradation occurs through lysosomal cytoplasmic autophagy.     

Ultrastructure de la spermiogenèse et du spermatozoïde de Loimosina wikoni et affinités phylétiques des Loimoidae (Plathelminthes, Monogenea, Monopisthocotylea)

In Loimosina, during spermiogenesis, the zone of differentiation of the spermatid contains two centrioles continued as two 9 +‘1’axonemes. One of the axonemes lengthens and will become the principal axoneme of the spermatozoon. The other axoneme is as long as the first one at the beginning of spermiogenesis, but is shorter in the mature sperm cell. The spermatozoon consists of several regions: (a) at the anterior end, the centriolar derivative of the principal axoneme; (b) a short region which shows cortical microtubules coinciding with external ornamentations; (c) a long uniflagellate region, with mitochondrion; (d) a biflagellate region containing the anterior slender part of the nucleus; (e) the posterior part of the nucleus, with no accompanying cytoplasmic organelles. Spermiogenesis and sperm structure in Loimosina differ from what is known in all other described monogeneans, excepting the monocotylid Heterocofyle to which they show close resemblances. However, the alteration of the second axoneme is more complete in Heterocofyle than in Loimosina. Comparative study of spermiogenesis and sperm ultrastructure thus shows an interesting coincidence with classical phylogenies of the monogeneans, in which the families Loimoidae and Monocotylidae are closely related. Chez Loimosina, pendant la spermiogenèse, la zone de différenciation de la spermatide contient deux centrioles prolongés par deux axonemes de type 9 +‘1′. L'un des axonemes s'allonge et deviendra l'axonème principal du spermatozoïde mûr. Le deuxième axontme est aussi long que le premier au début de la spermiogenèse, mais il est plus court dans le spermatozoïde mûr. Le spermatozoïde comprend: (a) à l'avant, le dérivé centriolaire de l'axonème principal; (b) une courte région contenant quelques microtubules corticaw longitudinaux coincidant avec des omementations extramembranaires; (c) une longue région miflagellée avec mitochondrie; (d) une région biflagellée contenant La partie antérieure effilée du noyau; (e) la région postérieure du noyau, sans organites cytoplasmiques accompagnateurs. La spermiogenèse et la structure du spermatozoïde de Loimosina sont différentes de ce qui est connu chez tous les autres Monogènes décrits, excepté le Monocotylidae Heterocofyle auquel elles ressemblent beaucoup. Toutefois, l'altération du deuxième axonème est moins complète chez Loimosina que chez Heterocotyle. L'étude comparée des spermatozoïdes et des spermiogenèses montre une bonne coincidence avec les phylogenèses classiques, dans lesquelles les familles Loimoidae et Monocotylidae sont proches.