The fine structure of Schistosoma mansoni sperm (Trematoda: Digenea).

The sperm of the blood fluke Schistosoma mansoni consist of a bulbous head 8 by 2 mum, with a rounded anterior tip and tapering posterior region, followed by a relatively short flagellum ca. 20 mum long. Electron microscopic observations revealed that these sperm are devoid of an acrosome, while a few undifferentiated mitochondria accumulate at the anterior part of the head. The nucleus appears dense, except for some electron-lucent patches. The flagellum starts at the basal body, posterior and slightly lateral to the nucleus, and the axial complex is of the 9 + 0 type. A layer of microtubules runs longitudinally, just beneath the plasmalemma, from the anterior part of the head to the initial part of the flagellum, where they overlap with the axial complex. It is suggested that this relatively rudimentary type of the S. mansoni sperm is probably related to the low activity required for fertilization.     

The cytology and ultrastructure of zoospores of Hydrurus foetidus (Chrysophyceae)

The unusual tetrahedral shape of Hydrurus foetidus (Vill.) Trev. zoospores is associated with a complex skeletal system of microtubules extending from a broad flagellar root (up to 19 microtubules) into each of three, pointed anterior processes. The posterior end, also pointed and supported by a separate set of microtubules, contains a single large chloroplast with a prominent posterior furrow containing mitochondrial elements. A large immersed pyrenoid is penetrated by paired thylakoids. There is no eyespot. Numerous large Golgi bodies occur immediately anterior to the nucleus and up to 5–6 contractile vacuoles lie near the cell surface at the anterior end. Two terminally inserted flagella extend from the cell surface, a long one serving for cell locomotion, and the other vestigial with an axonemal pattern of 9+0. The flagellar root system consists of: (1) a thin, striated rhizoplast extending from the basal body of the long flagellum and ramifying over the surface of a conspicuous, anteriorly directed, conical projection of the nucleus; (2) a broad microtubular root which emanates from near the basal body of the long flagellum and appears to function as a MTOC; (3) a compound root, consisting of a striated fiber and two associated microtubules, which runs alongside the basal body of the stubby flagellum before terminating at the cell surface; and (4) a short two-membered microtubular root, also associated with the basal body of the stubby flagellum. Other components of the flagellar apparatus include a large dense body near the proximal end of the basal body of the short flagellum, and a small, dense, core-like structure closely associated with one of its triplet fibers. The flagellar apparatus of H. foetidus is remarkably similar in ultrastructure to that of Chrysonebula holmesii Lund.     

The Spermatozoon of Brachionus plicatilis(Rotifera,Monogononta) With Some Notes on Sperm Ultrastructure in Rotifera

The spermatozoon of B. plicatilisis a thread–like cell with an anterior flagellar portion and a posterior cell body. The flagellum has a lateral ‘undulating membrane’, containing a folded longitudinal cisterna and an axoneme. The basal body of the axoneme is at the anterior tip. The axoneme lacks outer dynein arms and extends through the entire flagellar region and most of the cell body. The main portion of the flagellum and of the cell body contains a series of vesicles with tightly packed tubules that may serve as a cytoskeleton. The cell body contains a partly condensed nucleus, several mitochondria and some cytoplasm. Some elongated mitochondria are arranged in the postnuclear region. When the spermatozoon moves, the undulations propagate from the basal body at the flagellar tip. Late spermatids can be recognized by the nucleus and the flagellum being coiled and enclosed within a common cell membrane. As in other rotifers, there are cigar–like cell products (‘rods’) in the testes. The general organization of the cell, including the absence of an evident acrosome, resembles that of the other known monogonont sperm types.     

An ultrastructural investigation of Hrabeiella Pizl & Chalupský, 1984 (Annelida). II. The spermatozoon

The mature spermatozoa of the terrestrial non-clitellate annelid Hrabeiella periglandulata Pizl & Chalupsky, 1984 s.l. were examined using light and electron microscopy. They are about 150 mum long, filiform and extremely slender (maximum diameter, 450-475 nm). The acrosome is very elongate (about 25 mum), tapering and conical. Its transverse section is circular apically but shows an evident six-rayed symmetry in its basal region. The nucleus appears convex at both ends; apically, it extends laterally into the acrosome, and basally, it plugs into the centriolar region. The nucleus is about 23 mum long and has a rounded, tri- to pentalobed, slightly helical profile. The midpiece contains one elongate, free (paraxonemal) mitochondrion, 27 accessory tubules, which are slightly larger and more opaque than the axonemal microtubules; and seven electron-dense, non-membrane-bounded rods distributed around the axoneme. The flagellum tapers rapidly posteriorly. None of the observed similarities to the sperm (introsperm) of questids, protodrilids or other polychaetes seems to represent an immediate synapomorphy. None of the spermatozoal autapomorphies of the Euclitellata is shared by Hrabeiella.     

Transformation of the flagella and associated flagellar components during cell division in the coccolithophoridPleurochrysis carterae

Summary Immunofluorescence microscopy, conventional and high voltage transmission electron microscopy were used to describe changes in the flagellar apparatus during cell division in the motile, coccolithbearing cells ofPleurochrysis carterae (Braarud and Fagerlund) Christensen. New basal bodies appear alongside the parental basal bodies before mitosis and at prophase the large microtubular (crystalline) roots disassemble as their component microtubules migrate to the future spindle poles. By prometaphase the crystalline roots have disappeared; the flagellar axonemes shorten and the two pairs of basal bodies (each consisting of one parental and one daughter basal body) separate so that each pair is distal to a spindle pole. By late prometaphase the pairs of basal bodies bear diminutive flagellar roots for the future daughter cells. The long flagellum of each daughter cell is derived from the parental basal bodies; thus, the basal body that produces a short flagellum in the parent produces a long flagellum in the daughter cell. We conclude that each basal body in these cells is inherently identical but that a first generation basal body generates a short flagellum and in succeeding generations it produces a long flagellum. At metaphase a fibrous band connecting the basal bodies appears and the roots and basal bodies reorient to their interphase configuration. By telophase the crystalline roots have begun to reform and the rootlet microtubules have assumed their interphase appearance by early cytokinesis.Abbreviations CR1, CR2 crystalline roots 1 and 2 - CT cytoplasmic tongue microtubules - DIC differential interference contrast light microscopy - H haptonema - HVEM high voltage transmission electron microscopy - IMF immunofluorescence microscopy - L left flagellum/basal body - M metaphase plate - MT microtubule - N nucleus - R right flagellum/basal body - R1, R2, R3 roots 1, 2, and 3 - TEM transmission electron microscopy     

Morphology of testicular and post-testicular spermatozoa in Microstigmus arlei Richards, 1972 and M. nigrophthalmus Melo, 1992 (Hymenoptera: Apoidea: Pemphredoninae) with phylogenetic consideration

The sperm of Microstigmus arlei and Microstigmus nigrophthalmus are twisted in a spiral and consist of two regions: the head, formed by an acrosome and a nucleus, and the flagellum, formed by two asymmetric mitochondrial derivatives, a long centriolar adjunct, an axoneme (9+9+2) and two accessory bodies. The head shows a characteristic morphology. The acrosome is very long and is basically made up of a paracrystalline structure. In the central head region, the acrosome is inserted into the nucleus, which is observed coiling laterally around the paracrystalline structure. In the subsequent part of the spermatozoon the nucleus appears round in transverse sections, and over some length it is still penetrated by the acrosome until shortly distal to the flagellar insertion. At this point the nucleus forms an inverted cone-shaped projection. These morphological characteristics of acrosome and nucleus of the Microstigmus wasp have not been previously described in Apoidea and are useful for phylogenetic evaluation of this superfamily.     

Fine structure of the spermatozoa of Crassostrea gigas (Mollusca,Bivalvia)

We describe sperm ultrastructure and acrosome differentiation during spermiogenesis in Crassostrea gigas (Mollusca Bivalvia). The sperm cell is a uniflagellated cell of the primitive type. The head region contains a rounded or conical nucleus surmounted by small acrosome. This organelle consists of a membrane-bound acrosomal granule, the contents of which have a homogeneous density, except in the anterior region, which is positive for PTA. The acrosome also surrounds the perforatorium, which includes oriented fibrillar elements: this is the axial body. The middle piece contains four mitochondria encircling two perpendicular centrioles. The distal centriole is provided with a system of mechanical fixation to the plasma membrane, consisting of nine fibers in radial arrangement. The tail flagellum, about 50 m?m long, contains the usual microtubular axoneme. © 1993 Wiley-Liss, Inc.     

The spermatozoa of three species of Xenotrichulidae (Gastrotricha,Chaetonotida): the two “dünne Nebengeisseln” of spermatozoa in Heteroxenotrichula squamosa are peculiar para-acrosomal bodies

The spermatozoa of xenotrichulid gastrotrichs have been studied with the aim of supplying further characters for the phylogenetic analysis of Gastrotricha and to assess the reported biflagellarity of Heteroxenotrichula squamosa. Three species have been examined, belonging to the two hermaphroditic genera of xenotrichulids. The spermatozoa are filiform cells characterized by a scarcely condensed nucleus followed by a single mitochondrion and a flagellum with large accessory fibers. These show an obliquely striated cortex and a core containing some dense material. In Heteroxenotrichula squamosa and Xenotrichula punctata there is also a simple acrosome flanked by two para-acrosomal bodies which are curious long extracellular structures formed by a pile of electron-dense disks connected by thin threads. Xenotrichula intermedia lacks both acrosome and paraacrosomal bodies. The sperm model of xenotrichulids is very different from that of the Macrodasyida and Chaetonotida so far studied, thus supporting an isolated position of the family. The oblique striation of the tail's accessory fibers is similar in to the one period and inclination of the strated cylinder of macrodasyid gastrotrichs, thus being the only spermatological character shared by the two gastrotrich taxa.     

Fine structure of the spermatozoon of the viviparous teleost, Cymatogaster aggregata

The approximately 50 μm long sperm of Cymatoguster aggregata is composed of an elongate head (4 μm), an elongate mitochondria1 midpiece (3.5 μm) and a tail flagellum (roughly 40 μm). The sperm lacks an acrosome. Contained within depressions on one surface of the compressed head are a proximal centriole and a distal centriole separated by an electron dense, intercentriolar body. The anterior portion of the tail flagellum originates at the basal body (distal centriole) and is contained within an extracellular, flagellar tunnel within the mitochondria1 midpiece. The morphological similarity of C. uggregutu sperm to sperm of other internally fertilizing fishes supports the hypothesis that spermatozoan morphology is related to the mode of fertilization and that an elongate head and midpiece are specializations for internal fertilization.     

Ultrastructure of the spermatozoon and spermiogenesis in the interstitial annelid Potamodrilus fluviatilis

The ultrastructure of spermatozoa and its genesis (spermiogenesis) have been investigated in the interstitial annelid Potamodrilus fluviatilis. The mature spermatozoa are threadlike cells which are bent at the base of the flagellum, giving the cell a hairpinlike appearance. The acrosome consists of an unusual, long, flasklike vesicle with a granum in its basal part. The cylindrical nuclear region is characterized by a monolayer of vesicles enwrapping the posterior half of the nucleus. This region is endowed with a number of altered rodlike mitochondria. No middlepiece is present. The basal body of the flagellum is obliquely arranged with respect to the long axis, giving rise to a curved flagellum, which, along most of its length, exhibits a thick layer of vacuolized cytoplasm around the axoneme. During spermiogenesis, which occurs in the body fluid, spermatids develop at the surface of syncytial masses which have been formed during meiotic divisions. The acrosome protrudes in the distal part of the cell, while the basal body of the flagellum is shifted toward the proximal region, which connects the cell with the cytophore. These are unusual features in annelid spermiogenesis. As indicated in Discussion, the phylogenetic implications of these findings include the assumption that Potamodrilus is not related to any oligochaete or even any other clitellate group or species and, hence, has to be excluded from these taxa.     

A light and electron microscopical study of spermatogenesis in Hydra cauliculata

Morphological changes in the interstitial cells were studied during their differentiation into spermatozoa. Development of the spermatogonium involves an increase in nuclear and nucleolar size, and the formation of a dense mass of cytoplasmic ribosomes. The mature spermatozoon has a relatively simple structure. The head consists of a bullet shaped, homogeneous nucleus, which lacks an acrosome but bears distal membrane specializations. The middle piece is composed of four large spherical mitochondria at the base of nucleus. A single flagellum projects from one of the two centrioles lodged between the mitochondria. The flagellum appears early during development in the primary spermatocyte. During spermiogenesis microtubules associated with the basal body flagellum complex appear to define the axis of chromatin condensation.     

Flagellar apparatus duplication and partition, flagellar transformation during division in Entosiphon sulcatum.

Electron microscopic examination of serial sections of developmental stages of the flagellar apparatus during the cell cycle indicates that the basal bodies replicate in a semi-conservative manner and that there is a flagellar transformation over two cell cycles in euglenoids as in other algal flagellate groups. Two new pairs of basal bodies are formed, each pair comprising one parental and one newly developed basal body. There is a transformation of the parental dorsal flagellum containing a thin paraxonemal rod into a ventral flagellum bearing a large paraxonemal rod. Observation of the roots associated with the basal bodies shows that the dorsal root transforms into an intermediate root over two cell cycles following the transformation of the dorsal basal body/flagellum to a ventral one. Also the two ventral roots are newly formed in relation to the formation of two new phagotrophic apparatuses during the division. After the breakage of the connection between the parental basal bodies the two new pairs move apart and are guided/drawn by transverse microfibrillar bundles which connect them to opposite sides of the pellicle. The axis of the separation/migration of the pairs of basal bodies is parallel to the axis of elongation of the dividing nucleus.     

Ultrastructure of spermatids and spermatozoa in three polychaetes with modified biology of reproduction: Autolytus sp., Chitinopoma serrula,and Capitella capitata

Unlike the primitive type of spermatozoon found in most polychaetes, the spermatozoon of Autolytus has a bilateral symmetry with elongated nucleus, and the mitochondria surround the posterior part of the nucleus. A rather large disk-shaped acrosome is situated along one side of the anterior part of the nucleus. From the anterior margin of the distal centriole emerge long striated rootlets, which run along the nuclear envelope to the anterior part of the nucleus. The spermatozoon of Chitinopoma serrula has an elongated, slightly bent nucleus, a thimble-like acrosome apically on the anterior surface of the nucleus, and an elongated middle piece containing 4 rod-like mitochondria developed from spherical mitochondria surrounding the basal part of the tail flagellum. In the spermatozoon of Capitella capitata, both nucleus and middle piece are elongated compared to the primitive type. The large and conical acrosome is placed asymmetrically at the nucleus and consists of an acrosomal vesicle and subacrosomal substance. The greater part of the middle piece forms a collar around the initial part of the tail flagellum. The cytoplasm of the collar contains granular material. One or two small mitochondria lie around the 2 centrioles at the base of the nucleus.

These types of spermatozoa represent early steps in the evolution of modified spermatozoa combined with changed biology of reproduction. The modified spermatozoa are larger than the primitive ones.     

Fine structure of the spermatozoon of Marthasterias glacialis (Linnaeus) (Echinodermata; Asteroidea), with special reference to acrosomal morphology

The sperm of Marthasterias glacialis (Linnaeus) was studied by light and electron microscopy. It is a long uniflagellated cell of the “primitive” type. The head has a spherical shape and contains a nucleus with a spheroid acrosome lying in a cup-shaped anterior fossa. The acrosome is formed by an acrosomal vesicle surrounded by the periacrosomal material. The basal specializations of the acrosomal vesicle show a clear differentiation of its constituents resembling the structure of membrane. The midpiece contains a very large annular mitochondrion which encircles two perpendicular centrioles. The distal centriole is in close association with a pericentriolar radial complex. The tail, containing a common microtubular axoneme, is projected to a variable position.     

Ultrastructure of spermatogenesis in the sea star,Asterina minor

The ultrastructural features of spermatogenesis were investigated in the hermaphroditic sea star Asterina minor. The primordial germ cells in the genital rachis contain small clusters of electron-dense material (nuage material) and a stack of annulate lamellae. They also have a flagellum and basal body complex situated close to the Golgi complex. After the development of the genital rachis into the ovotestis, spermatogenic cells increase in number and differentiation begins. Nuage material is observed in spermatogonia, but it gradually disappears in spermatocytes. The annulate lamellae do not exist beyond the early spermatogonial stage. By contrast, a flagellum and basal body complex are found throughout spermatogenesis. The Golgi-derived proacrosomal vesicles appear in the spermatocyte and coalesce to form an acrosomal vesicle in the early spermatid. The process of acrosome formation is as follows: (1) a lamella of endoplasmic reticulum (ER) continuous with the outer nuclear membrane encloses the posterior portion of the acrosomal vesicle; (2) the vesicle attaches to the cell membrane with its anterior portion; (3) periacrosomal material accumulates in the space between the acrosomal vesicle and the ER; (4) the nucleus proper changes its features to surround the acrosome; (5) amorphous, electron-dense material is deposited under the electron-dense disk; and (6) the nucleus forms a hollow opposite the electron-dense material.     

Cryopreservation of Atlantic croaker spermatozoa: evaluation of morphological changes.

The spermatozoon of the Atlantic croaker (Micropogonias undulatus) is a primitive type in that it lacks an acrosome. The kidney-shaped head has a diameter of about 1.5 microns and is occupied by a granular and electron-dense nucleus. The short midpiece contains 3 spherical mitochondria and encircles the basal body of the flagellum but is separated from it. The flagellum consists of the typical 9 + 2 axoneme and surrounding plasma membrane but lacks a lateral ridge. Spermatozoa of Atlantic croaker diluted in either NaCl or sodium citrate solutions with or without DMSO were examined with the electron microscope before freezing in liquid nitrogen and after thawing. Damage following cryopreservation appeared to be greater to the mitochondria, plasma membrane, and 9 + 2 axoneme than to the nucleus. The incidence of postthaw damage in spermatozoa diluted with NaCl solutions containing DMSO was remarkably lower than that with either pure NaCl solutions, pure sodium citrate solutions, or sodium citrate solutions containing DMSO.     

Ultrastructural and immunocytological studies on the rhizoplast in the chrysophycean alga Ochromonas danica

The rhizoplast, a striated band elongating from the flagellar basal body to the nucleus, is conspicuous in cells of Ochromonas danica Prings. In interphase cells, it runs from the basal body of the anterior flagellum to the space between the nucleus and the Golgi body. In O. danica, the rhizoplast duplicates during mitosis and the two rhizoplasts serve as mitotic poles. In the present study, we reinvestigated mitosis of O. danica using transmission electron microscopy and immunofluorescence microscopy, especially focusing on the rhizoplast. The nuclear envelope became dispersed during metaphase, and the rhizoplasts from two sets of the flagellar basal bodies functioned as the mitotic poles. Immunofluorescence microscopy using anti‐α‐tubulin, anti‐centrin and anti‐γ‐tubulin antibodies showed that centrin molecules were localized at the flagellar basal bodies, whereas γ‐tubulin molecules were detected at the rhizoplast during the whole cell cycle.     

The spermatogenesis and the sperm structure of Terebrantia (Thysanoptera, Insecta)

Spermatogenesis and the sperm structure of the terebrantian Aeolothrips intermedius Bagnall are described. Spermatogenesis consists of two mitotic divisions; the second is characterized by the loss of half of the spermatids, which have pyknotic nuclei. Early spermatids have two centrioles, but when spermiogenesis starts, a third centriole is produced. The three basal bodies give rise to three flagella; later these fuse into a single flagellum which contains three 9 + 0 axonemes. The basal bodies are surrounded by a large amount of centriole adjunct material. During spermiogenesis this material contributes to the shifting of the three axonemes towards the anterior sperm region parallel to the elongating nucleus, and it is transformed into a dense cylinder. In the mature spermatids the three axonemes amalgamate to create a bundle of 27 doublet microtubules. Near the end of spermiogenesis the dense cylinder of the centriole adjunct lies parallel to the nucleus and the axonemes. It ends where the mitochondrion appears at half-sperm length. We confirm that Terebrantia testes have a single sperm cyst; their sperm are characterized by a cylindrical nucleus, three axonemes fused into one, a small mitochondrion and a short cylindrical centriole adjunct which corresponds to the dense body described in a previous work. The acrosome is lacking. At the midpoint of the anterior half of the sperm the outline of the cross-section is bilobed, with the nucleus contained in a pocket evagination of the plasma membrane. These characters are discussed in light of a comparison between Tubulifera and Terebrantia.     

The short spermatodesm of Arge pagana (Hymenoptera: symphyta)

In the seminal vesicle of the 'symphyta'Arge pagana the spermatozoa are stored in motile spermatodesm bundles, maintained by an anterior cap of extracellular material. This cap consists of a denser cortex and of an internal matrix, where part of the sperm heads are embedded. The number of spermatozoa per bundle is variable. The spermatozoa are short, only 30microm long, with a head region of about 23microm, and a very short flagellum of about 7microm. The head includes the acrosome, with a perforatorium, and the nucleus. The flagellum consists of an axoneme, with a 9+9+2 microtubule pattern, a centriolar adjunct, two mitochondrial derivatives and two accessory bodies. The mitochondrial derivatives are very slender and of different lengths. The longer begins at the base of the nucleus, while the shorter one starts just below the base of the centriolar adjunct. This latter is asymmetric and appears at the nuclear base, extending parallel to the axoneme up to the anterior end of the smaller mitochondrial derivative. The short spermatodesmata and the small mitochondrial derivatives characterize the A. pagana sperm. In addition, the centriolar adjunct asymmetry and the occurrence of spermatodesm bundles might be considered plesiomorphic states present in the basal Tenthredinoidea.     

Spermatogenesis and ultrastructure of the spermatozoa of Seison nebaliae (Syndermata)

 The spermatozoa of Seison nebaliae are characterized by an elongated sperm body, a filiform nucleus, and an anteriorly inserting external cilium with a 9×2+2 axoneme pattern. In the sperm body a frontal, middle, and hind region can be distinguished. The frontal region contains an acrosomal vesicle, a perforatorium, a basal body, and a pair of apical dense bodies; an accessory centriole is absent. The middle region is characterized by several so-called filamental plates. One large mitochondrion and one pair of accessory tubular structures are located in the middle and hind region. The hind region also contains two rows of dense bodies. Accessory tubular structures and filamental plates are autapomorphies of S. nebaliae. The shared appearance of the dense bodies in spermatozoa of species of the taxa Seison and the Acanthocephala founds their sister-group relationship, while the anterior insertion of the cilium in the spermatozoa of these taxa and in the Rotifera confirms the monophylum Syndermata Ahlrichs, 1995. Accepted: 5 August 1998