Ultrastructure of spermiogenesis in the gastropod Calliotropis glyptus Watson (Prosobranchia: Trochidae)with special reference to the embedded acrosome

Testicular spermatozoa and sperm development in the archaeogastropod Calliotropis glyptus Watson (Trochoidae: Trochidae) are examined using transmission electron microscopy and formalin-fixed tissues. During spermiogenesis, the acrosome, formed evidently through fusion of Golgi-derived proacrosomal vesicles, becomes deeply embedded in the condensing spermatid nucleus. Two centrioles (proximal and distal), both showing triplet microtubular substructure, are present in spermatids—the distal centriole giving rise to the sperm tail and its associated rootlet. During formation of the basal invagination in the spermatid nucleus, centrioles, and rootlet move towards the nucleus and come to lie totally within the basal invagination. Mitochondria are initially positioned near the base of the nucleus but subsequently become laterally displaced. Morphology of the mature spermatozoon is modified from that of the classic primitive or ect-aquasperm type by having 1) the acrosome embedded in the nucleus (the only known example within the Mollusca), 2) a deep basai invagination in the nucleus containing proximal and distal centrioles and an enveloping matrix (derived from the rootlet), 3) laterally displaced periaxonemal mitochondria, and 4) a tail extending from the basal invagination of the nucleus. Implantation of the acrosomal complex and centrioles within imaginations of the nucleus and lateral displacement of mitochondria effectively minimize the length of the sperm head and midpiece. Such modifications may be associated with motility demands, but this remains to be established. The unusual features of C. glyptus spermatozoa, though easily derivable from ‘typical’ trochoid sperm architecture, may prove useful in delineating the genus Calliotropis or tracing its relationship to other genera within the trochid subfamily Margaritinae.     

The fine structure of motile cells in the generaUlvaria andMonostroma,with special reference to the taxonomic position ofMonostroma oxyspermum (Ulvophyceae,Chlorophyta)

The zoospores and isogametes ofUlvaria obscura var.blyttii, the isogametes ofMonostroma bullosum, and the anisogametes ofM. grevillei have a flagellar apparatus with counterclockwise absolute orientation and terminal caps, and therefore belong to theUlvophyceae. On the basis of the absence or presence of body scales and the morphologies of certain flagellar apparatus components,Ulvaria obscura var.blyttii is retained in theUlvales, whileM. bullosum, M. grevillei andM. oxyspermum are referred to theUlotrichales. Differences in scale morphology, certain flagellar apparatus components, and early thallus ontogeny support the transfer ofM. oxyspermum to the genusGayralia. Mating structures and their positional relationships within the cell are described from the gametes examined. A plasmalemma-associated plaque that may be a degenerate mating structure occurs in someG. oxysperma motile cells.     

Fine structure of spermiogenesis with special reference to the spermatid morulae of the freshwater mussel Prisodon alatus (Bivalvia,Unionoidea)

Within the testicular cysts of the mussel Prisodon alatus are numerous somatic host cells described as Sertoli cells (SC), each containing a variable number of young spermatid morulae. Among them, several free spermatid morulae, spermatids, and spermatozoa were observed. Each free spermatid morula is surrounded by an external membrane. The early spermatids enclosed within the morulae have dense and homogeneous chromatin, and the cytoplasm occupies little space around the nucleus. Later, during spermiogenesis, the SC show lysis and disrupt to liberate the spermatid morulae. The membrane of the free morula is then disrupted, releasing the young spermatids. The SC disappear just after the appearance in the testis of a large number of free young spermatids. The nucleus of each free spermatid becomes gradually smaller and denser by the appearance of a granular pattern of condensed chromatin. During the maturation phase of the spermatids, the cytoplasm becomes more voluminous, and mitochondria and centrioles are more evident. Then, flagellogenesis occurs, and the nucleus gradually condenses into thicker strands. In the mature sperm, the apical zone has a disc-shaped acrosomal vesicle and the midpiece contains five mitochondria and two centrioles located at the same level. The flagellum has the common 9+2 microtubular pattern. The results are discussed with particular reference to Sertoli cells and clusters of spermatid morulae with those of species of closely related taxa in the bivalves. J. Morphol. 238:63–70, 1998. © 1998 Wiley-Liss, Inc.     

Morphology of the jaw apparatus in 8 species of Patellogastropoda (Mollusca, Gastropoda) with special reference to Testudinalia tesulata (Lottiidae)

The fine structure of the jaw apparatus was studied by scanning electron microscopy in eight species of Patellogastropoda. The jaw apparatus is an unpaired two-layered dorsolateral structure with anterior and posterior wings attached to the odontophore by muscles. The jaw of Testudinalia tesulata (O.F. Müller, 1776) is a derivative of the cuticle typical for the foregut. The tissue forming the jaw is a specialized foregut epithelium (gnathoepithelium), consisting of a special type of cells called gnathoblasts. The jaw grows in areas of the epithelium characterized by high concentration of electron-dense vesicles, ER and long microvilli that penetrate deep into the jaw plate. This indicates that the gnathoblasts take an active part in jaw growth. In most cases, these areas of the gnathoepithelium are highly folded. The main differences between the species studied are form and thickness of the frontal edge of the jaw. These differences do not correlate with the systematic position of the species studied but likely depend more on the feeding mode. The transmission electron microscopy studies yielded new morphological criteria for comparison between various gastropod species and other members of Trochozoa, in particular, Annelida. The jaws of Annelida are cuticular structures formed on the surface of specialized epithelial cells, often also called gnathoblasts. The jaw of Patellogastropoda can be attributed to the first type of annelid jaw formation characterized by an epithelium with long microvilli and continuous growth.     

An integrative taxonomic approach to infer the systematic position of Chalepotaxis Ancey, 1887 (Gastropoda: Stylommatophora: Helicarionidae)

In the absence of knowledge about its anatomy, the systematic position of the genus Chalepotaxis, which inhabits a large part of South East Asia, has been historically dubious. The genitalia, sole of the foot and the caudal region of the type species, Chalepotaxis infantilis (Gredler, V. 1881. Zur Conchylien-Fauna von China. III. Stück. Jahrbücher der Deutschen Malakozoologischen Gesellschaft 8, 110–128), are described, which place this genus into the Helicarionidae family. DNA markers (cytochrome oxidase subunit I [COI] and 28S rRNA genes) corroborate this assignment and unequivocally remove the species from the Camaenidae (=Bradybaenidae) and Ariophantidae, where it had previously been placed. Radular morphology of the type species is also re-described and illustrated.     

Ultrastructure of Stylodinium Iittorale (Dinophyceae) with special reference to the stalk and apical stalk complex

The ultrastructure of Stylodinium littorale Horiguchi et Chihara, a marine, sand-dwelling coccoid dinoflagel-late, was investigated with special emphasis on its stalk and the apical stalk complex. The dinoflagellate alternates between non-motile and motile cells in its life cycle. The non-motile cell possesses a long and distinct stalk. The stalk, consisting of a main cylindrical part and a holdfast, is firmly attached to a thecal plate (the apical pore plate). A part of its proximal portion is hollow and V-shaped in section. The V-shaped hollow space is underlain by a projection from the apical pore plate. An apical stalk complex is present in the motile cells and consists of a large apical pore plate and mucilaginous material. The apical pore plate is depressed into the cell, but has a narrow central tubular projection. The mucilaginous stalk-building material is stored between this plate and the outer plate membrane. The tubular projection of the apical pore plate corresponds to the apical pore of other dinoflagellates and its lumen is filled with electron-dense material. The structure of the apical stalk complex is compared with the homologous structure in Bysmatrum arenicola, the only other example of an apical stalk complex that has been investigated. A general ultrastructural survey revealed that S. littorale possesses a typical dinoflagellate cellular structure.     

Ultrastructure of the crocodile kidney (Crocodylus acutus) with special reference to electrolyte and fluid transport

The study of the ultrastructure of the kidney tubules of the crocodile was made to compare the cellular structure with the capacity for electrolyte resorption and the ability to create an osmotic gradient across the tubular wall. The crocodile tubular cells were found to differ from the mammalian tubular cells in that they do not have basal infoldings, but instead have open lateral spaces between the cells, similar in many aspects to those found in the mammalian gallbladder. The physiological role of these lateral spaces in solute and fluid transfer is discussed.     

Ultrastructure of Octodon degus spermatozoon with special reference to the acrosome

The ultrastructure of spermatozoa from the cauda epididymidis and vas deferens of Octodon degus-a Chilean hystricomorph rodent-is presented. The head of spermatozoa measured 7.7 micrometer long by 5.9 micrometer wide and the tail was 41 micrometer long. The head was flattened dorso-ventrally and ovate in outline. The acrosome was the most distinctive feature of O. degus spermatozoa. In a frontal view of the head, the rim of the acrosome surrounding the nucleus had the shape of an inverted U. The acrosomal region covering the plane of the flattened head exhibited dome-shaped protrusions. Transverse or sagittal sections of acrosomal protrusions showed that the plasma membrane and outer acrosomal membrane were evaginated, while the inner acrosomal membrane followed the contour of the nucleus. The protrusions were not distributed at random and they were absent in the equatorial segment and in the rim of the acrosome. In frontal views, near the boundary between the acrosome and post-acrosomal region, fine rods about 170 nm long ran obliquely on the caudal part of the equatorial segment. Behind the same boundary, the post-acrosomal region showed a serrated border. Phosphotungstic acid treatment at pH 0.3 produced staining at the surface of the sperm as well as within a superficial layer of the marginal thickening of the acrosome and on the acrosomal protuberances.     

Ultrastructural observations of the spermiogenesis in the Parotoplaninae (Plathelminthes,Proseriata) with special reference to a striated appendage of the intercentriolar body

Summary The spermiogenesis of three species of the Parotoplaninae (Otoplanidae, Proseriata) is described based on electron-microscopical observations. Special reference is given to organelles which do not persist in mature male gametes. One of these organelles is a striated appendage of the intercentriolar body. This differentiation has not been reported from any other plathelminth taxa up to now. The striated appendage, which may serve as a strengthening element, is hypothesized to be an autapomorphic feature of the Parotoplaninae.     

Nuclear morphogenesis during spermiogenesis in the nudibranch molluscHypselodoris tricolor (Gastropoda,opisthobranchia)

An electron microscope study was carried out on Hypselodoris tricolor spermatids to describe the development of the nuclear morphogenesis and investigate the possible cause(s) of the change in the shape of the spermatid nucleus during spermiogenesis. Three different stages may be distinguished in the course of the nuclear morphogenesis on the basis of the morphology and inner organization of the nucleus. Stage 1 spermatid nuclei are spherical or ovoid in shape and the nucleoplasm finely granular in appearance. Stage 2 nuclei exhibit a disc- or cup-shaped morphology, and the chromatin forms short, thin filaments. During stage 3, a progressive nuclear elongation takes place, accompanied by chromatin rearrangement, first into fibers and then into lamellae, both formations helically oriented. A row of microtubules attached to the nuclear envelope completely surrounds the nucleus. Interestingly, the microtubules always lie parallel to the chromatin fibers adjacent to them. Late stage 3 spermatids show the highest degree of chromatin condensation and lack the manchette at the end of spermiogenesis. Our findings indicate the existence of a clear influence exerted on the chromatin by the manchette microtubules, which appear to be involved in determining the specific pattern of chromatin condensation in Hypselodoris tricolor.     

Spermatozoon structure and spermiogenesis in Nassarius kraussianus (Gastropoda,Prosobranchia, Nassariinae)

Summary

The testis of Nassarius kraussianus (Nassariinae) produces two types of spermatozoa, a motile euspermatozoon and a non-motile paraspermatozoon. The euspermatozoon is filiform and about 95/μm long. The elongated head (40 μm long) is comprised of a slender nucleus (about 0.5 μm diameter) which is penetrated throughout by an intranuclear canal housing the anterior portion of the axoneme. A short (about 2 μm long) conical acrosome surmounts the nucleus anteriorly. The mid-piece (23 μm in length) consists of six to seven modified mitochondria which are helically arranged around the axoneme. Posterior to the mid-piece the tail is composed of a short glycogen piece and an end piece. The paraspermatozoon is spindle-shaped (about 50 μm long) and contains multiple (16–20) axonemes the basal bodies of which fuse anteriorly. Posteriorly, numerous small mitochondria and electron-dense bodies lie between the axonemes. Structural changes during eu- and paraspermiogenesis mirror those described for other species of gastropod mollusc with dimorphic spermatozoa. However unlike other molluscs, the cytoplasmic bridges which connect developing spermatids contain well developed stacks of endoplasmic reticulum which form a continuum with that in the cytoplasm of the spermatids. These structures may in some way facilitate the synchronous development of the spermatozoa.     

Ultrastructure of the rabbit neurohypophysis with special reference to the release of hormones

Summary The ultrastructure of normal neural lobes of adult rabbits is described. The major part consists of non-myelinated fibres containing neural swellings at intervals. These enclose the neurosecretory granules, mitochondria and a few microtubules. The swellings are connected by narrow nerve fibres with parallel neurotubules but no granules. The Herring bodies resemble large neural swellings and may contain many neurotubules. They are sometimes enclosed by multilamellate sheaths. True myelinated nerve fibres full of granules also occur. The relationship between the neural swellings and pituicytes is discussed. The pituicyte cytoplasm contains many delicate fibrils but it does not resemble an active secretory cell.The blood vessels are characterised by an unusually wide perivascular space containing two condensed layers of basement membrane. These layers can be traced into channels which extend from the perivascular spaces and break up the tissue into lobules. It is suggested that these channels form a mucopolysaccharide spongework that may be important in relation to the release of hormones.The common feature of ether-treated, dehydrated and immature animals is the absence of electron-dense cores from the neurosecretory granules. Such glands are not completely depleted of hormones and much of the hormonal activity is still associated with a sedimentable fraction. Loss of electron density may be due to diffusion of the neurophysin carrier or to a change in configuration of the neurophysin molecules resulting in inaccessibility of both osmiophilic and hormone binding sites. The unbound hormone may be stored in the mucopolysaccharide sponge-work and released gradually into the blood stream.This work is offered as a tribute to Dr. Berta Scharrer on the occasion of her 60th birthday and in appreciation of her leading contribution over many years towards the understanding of the concept of neurosecretion.We are grateful to the Wellcome Trust for providing the Siemens Elmiskop 1 electron microscope used at the Dept. of Human Anatomy, Oxford, and to the D.S.I.R. for other assistance. We also acknowledge valuable discussions with our colleagues, especially Professors H. Heller and W. Bartley.     

Ultrastructure of spermiogenesis in Plagioscion squamosissimus (Teleostei, Perciformes, Sciaenidae)

Spermiogenesis in Plagioscion squamosissimus occurs in cysts. It involves a gradual differentiation process of spermatids that is characterized mainly by chromatin compaction in the nucleus and formation of the flagellum, resulting in the spermatozoa, the smallest germ cells. At the end of spermiogenesis, the cysts open and release the newly formed spermatozoa into the lumen of the seminiferous tubules. The spermatozoa do not have an acrosome and are divided into head, midpiece, and tail or flagellum. The spermatozoa of P. squamosissimus are of perciform type with the flagellum parallel to the nucleus and the centrioles located outside the nuclear notch.     

Palynological characters of Glycyrrhiza,Glycyrrhizopsis, and Meristotropis (Leguminosae), with special reference to their taxonomic significance

Abstract The pollen morphology of 11 species of the genus Glycyrrhiza L. with one from each of the genera Glycyrrhizopsis Boiss. & Bal. and Meristotropis Fisch. & C. A. Mey. was investigated by scanning electron microscopy. In pollen morphology, the main differences between Glycyrrhizopsis and Glycyrrhiza are: Glycyrrhizopsis—pollen grains 36.63 × 40.42 μm in size, oblate spheroidal in shape; and Glycyrrhiza—pollen grains 24.47–33.18 × 23.82–31.83 μm in size, prolate spheroidal in shape. Glycyrrhizopsis and Glycyrrhiza should be recognized as two distinct genera based on palynological and morphological characters. Meristotropis and Glycyrrhiza are similar in many important palynological and morphological characters, suggesting that the two should be merged. In Glycyrrhiza, two types of pollen grains, 3‐lobed‐circular or subtriangular in polar view, are found in different species, in accordance with morphological differences in the two groups, shedding light on the classification and evolution of the genus.     

Palynological characters of Glycyrrhiza,Glycyrrhizopsis,and Meristotropis(Leguminosae),with special reference to their taxonomic significance

Li X-Y.1992.Studies on germplasm of Glycyrrhiza by using different taxonomic methods.Advances in Plant Taxonomy in Northwest China 1:7-24.

Li X-Y.1993.A study of the system and new taxa of genus Glycyrrhiza L.Bulletin of Botanical Research 13(1):14-43.

Turrill WB.1937.Glycyrrhizopsis syriaca Turrill.Bulletin of Miscellaneous Information 2:79.

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Molecular phylogeny of small brown algae,with special reference to the systematic position of Caepidium antarcticum (adenocystaceae,ectocarpales)

Nuclear ribosomal DNA (3′-SSU, ITS, 5′-LSU) and plastid-encoded (rbcL and Rubisco spacer) sequences were determined in Caepidium antarcticum and compared to homologous sequences of relatives from Ectocarpales, Scytothamnales, and other brown algae. Plastidial sequences confirmed a previous conclusions from nuclear ribosomal sequences that some taxa with stellate plastids (Asterocladon and relatives) form the closest outgroup to the Ectocarpales as yet identified. To reconcile nomenclature with the clades resolved in recent molecular studies, we propose a subdivision of the Ectocarpales in five families. Plastidial sequences support the recent proposal of Adenocystaceae, and all sequences suggest that Caepidium should be included in this family. As a further result, Geminocarpus was shown to belong to the same clade as Pylaiella and a number of other brown algae with an isomorphic life history and discoid plastids. We recognise this clade, whose correct name is Acinetosporaceae, as another family in the Ectocarpales. We also propose to unite a number of genetically related taxa, which were formely classified in different families, in an extended Chordariaceae. The remaining species of the Ectocarpales belong to Scytosiphonaceae and to Ectocarpaceae, the latter containing only Ectocarpus and Kuckuckia.