Differentiation of Male Gametes in Gracilaria verrucosa (Rhodophyta, Gracilariales)

The development of male gametes (spermacia) in the red alga Gracilaria verrucosa has been studied using methods of transmission electron microscopy. Early spermatangia located along the wall of the conceptacle show an elongated shape in the thin sections. In the central part of the electron-dense cytoplasm of these cells there is a nucleus; numerous fibrous vesicles are arranged in the periphery. During the process of differentiation, the spermatangia become more rounded in shape and a large spermatangial vesicle is developed. The subsequent development of spermatium is accompanied by polarization of the spermatangium and the subsequent excretion of the spermatangial vesicle. The spermatia are oval cells containing a nucleus and fibrous vesicles. The process of differentiation of male gametes in G. verrucosa does not differ from that in five species of the genus Gracilaria, where it has already been studied. However, any conclusions about the degree of similarity between the spermatia in all the studied species can be made only after a detailed comparative analysis of the ultrastructural characteristics of these gametes.     

Cell shape in the algaPediastrum (Hydrodictyaceae; Chlorophyta)

Summary Species ofPediastrum, a genus in which the colonies assemble from aggregating zoospores, differ in the number and form of prongs on peripheral cells and the amount of space between cells of the colony; cell shape appears to be genetically based. Peripheral cells of theP. boryanum colony, for example, have two prongs per cell;P. simplex has one prong per cell. Prong extension is suppressed in the interior cells ofP. boryanum, but prong sites have been reported in scanning electron micrographs of the cell walls. A mutant unicellular strain in which cells of the colony separate after attaining typical form reveals several prong sites (6 or more) in each cell. Multiple suppressed prong sites are evident inP. simplex cells as well. Polyeders, 4- and 5-pronged unicells, occur in the life cycle ofP. simplex. Based on these observations and a recent report byMarchant (1979) of a microtubule organizing center associated with the prongs, it is suggested that several microtubule organizing centers are to be found in zoospores ofPediastrum species and may be related to species differences in cell shape.Research supported in part by Argonne Center for Educational Affairs, U.S. Department of Energy, under contract No. W-31-109-ENG-38.     

Fine-grained secretory cells in the intestine of the lancelet,Branchiostoma (Amphioxus) lanceolatum,studied by light microscopy

Summary In the posterior part of the mid-gut epithelium in the lancelet, Branchiostoma lanceolatum, fine-grained cells occur. The appearance of the these cells is conspicuous with a basal and an apical swelling with small secretory granules. At the end of the secretion cycle the granular content is released into the gut lumen. The secretion product seems to consist of proteins and probably has an enzyme function. The restricted localization, the fine granulation, and the characteristic shape are features, that make these cells distinguishable from other secretory cells in the lancelet intestinal epithelium. A possible endocrine capacity of the cells is discussed.This work was supported by grant 2124-23 from the Swedish Natural Science Research Council and by grants from the Faculty of Science, University of Stockholm, Sweden.     

Ultrastructure of the kidney of a South American caecilian,Typhlonectes compressicaudus (Amphibia,Gymnophiona)

Summary The ultrastructure of the distal nephron, the collecting duct and the Wolffian duct was studied in a South American caecilian, Typhlonectes compressicaudus (Amphibia, Gymnophiona) by transmission and scanning electron microscopy (TEM, SEM). The distal tubule (DT) is made up of one type of cell that has a well-developed membrane labyrinth established both by interdigitating processes and by interlocking ramifications. The processes contain large mitochondria, the ramifications do not. The tight junction is shallow and elongated by a meandering course. The connecting tubule (CNT) is composed of CNT cells proper and intercalated cells, both of which are cuboidal in shape. The CNT cells are characterized by many lateral interlocking folds. The intercalated cells have a dark cytoplasm densely filled with mitochondria. Their apical cell membrane is typically amplified by microplicae beneath which a layer of globular particles (studs) is found. The collecting duct (CD) is composed of principal cells and intercalated cells, again both cuboidal in shape. The CD epithelium is characterized by dilated intercellular spaces, which are often filled with lateral microfolds projecting from adjacent principal cells. The apical membrane is covered by a prominent glycocalyx. The intercalated cells in the CD are similar to those in the CNT. The Wolffian duct (WD) has a tall pseudostratified epithelium established by WD cells proper, intercalated cells and basal cells. The WD cells contain irregular-shaped dense granules located beneath the apical cell membrane. The intercalated cells of the WD have a dark cytoplasm with many mitochondria; their nuclei display a dense chromatin pattern.Research fellow of the Alexander von Humboldt Foundation     

Structural organization of ovarian follicle cells in the cotton bug (Dysdercus intermedius) and the honeybee (Apis mellifera)

Summary The somatic epithelia of Dysdercus and Apis follicles were analyzed by electron microscopy, and the patterns of F-actin and microtubules were studied by fluorescence microscopy. The epithelia in both species differ considerably in shape and in the organization of the cytoskeleton. During previtellogenic stages, the epithelium consists of columnar-shaped cells with small (Dysdercus) or no (Apis) lateral intercellular spaces. During vitellogenesis, the follicle cells round up; the intercellular spaces increase in size in Dysdercus follicles, whereas in Apis follicles they remain small. Along the basal surface of the follicle cells, there are conspicuous parallel bundles of microfilaments perpendicular to the anteroposterior axis of the follicles. In the honeybee, these microfilament bundles are present in long filopodia, most of which are embedded in thickenings of the basement membrane and extend over the surfaces of neighbouring cells. In the cotton bug, the basal surface of the follicle cells is thrown into parallel folds. The microfilament bundles are located just underneath the cell membrane where the folds contact the basement membrane. In the polar regions of the Dysdercus follicle, the epithelial cells become flat and adhere to each other without forming intercellular spaces. The basement membrane is particularly thick in the polar areas; this has also been observed in Apis follicles around the intercellular bridge connecting oocyte and nurse cells.     

Leaf morphology of a facultative rheophyte,Farfugium japonicum var.luchuense (Compositae)

The gross morphology and anatomy of leaves in a facultative rheophyte,Farfugium japonicum var.luchuense, were examined in order to clarify how the two characters are correlated with one another and how the facultative rheophyte differs from obligate rheophytes in leaf morphology and anatomy. Most rheophytes of the variety have narrowly cuneate leaf base, while most inland plants usually have truncate to cordate one, although the habitat-morphology correlation is not so clear. The leaf shape or the divergence angle of leaf base is strongly correlated with the number of primary veins and intervein-distance dependent on the number of cells intervening between veins. This makes a marked contrast to many reported cases of obligate rheophytes in which the leaf shape is strongly correlated with cell size. There is a rough tendency that narrower leaves of rheophytes have a thicker cuticular layer. However, the cell size and the volume (area) of intercellular space differ only slightly with the leaf shape.     

Taxonomic study of the genusMyagropsis (Cystoseiraceae,Phaeophyta)

The generic names of the brown algaeMyagropsis, Cystoseira andCystophyllum have been used in Japan, Korea and China for a small group of seaweeds whose limits have not been clearly understood. Studies on the development of the eggs and subsequent germlings show that substantial differences occur betweenCystoseira andMyagropsis. Myagropsis Kützing is distinguished fromCystoseira C. Agardh by the following characteristics: (1) the tongue cell is undivided during development of the conceptacle; (2) paraphyses are projected from the conceptacle ostiole and become entangled; (3) during development, oospore germlings are mixed among paraphyses projecting from the ostiole; (4) oospores are large, with eight nuclei at maturity; (5) thirty-two primary rhizoids are produced on the germlings; and (6) the thallus is bilateral in organization. The shape and size of vesicles, their formation, and the presence of cryptostomata have been used as specific characters, but their use cannot be continued. It is concluded that the genusMyagropsis is monotypic, with a single species,M. myagroides (Turner) Fensholt. The status of this species is also discussed.     

Notes onLaboulbenia coneglanensis (Ascomycetes, Laboulbeniales) in Japan

Laboulbenia coneglanensis isolated from Japanese harpaline carabids is described and photographed. It is compared morphologically withL. flagellata from Japan and Europe, which is similar in appearance. The most important difference between the two species is in antheridial character and host range. Other characters such as coloration, perithecial shape, especially the shape of the perithecial apex, and size of ascospores are also useful for distinction.Laboulbenia ophoni var.dilatata described by Maire (1920) is regarded as a synonym ofL. coneglanensis.     

Taxonomic and functional implications of stigma morphology in species ofCassia,Chamaecrista, andSenna (Leguminosae:Caesalpinioideae)

Two stigma forms occur inChamaecrista andSenna, but only one inCassia. In the common chambered form, a stigma pore is positioned on the reflexed style tip and is the entrance to a tapering chamber. The pore rim is fringed by hairs which vary in number, size, distribution and shape. In the alternative form the stigma is situated at the apex of the curved style and is crateriform. The crater rim is fringed by hairs of variable number and shape. The stigmatic hairs are predominantly unicellular and cutinized. Stigma and hair differences aid in the taxonomy of the genera. Their functions in pollination biology are discussed.     

Nutlet morphology in Hemigenia R.Br. and Microcorys R.Br. (Lamiaceae)

Nutlets of Hemigenia R.Br. and Microcorys R.Br. were examined using SEM. Significant variation, mainly useful at the infrageneric level, was found in nutlet shape, nature of the attachment scar, nature of surface sculpturing, exocarp cell shape and sculpturing, and nature of the indumentum. Typical nutlets are ovoidal, strongly reticulate or rugose. The exocarp cells are isodiametric and convex to papillate. Also common are cylindrical nutlets, often with longitudinal ridging and papillate exocarp cells. Surface pitting and concave exocarp cells are rare. A cladistic analysis of nutlet characters suggests both Hemigenia and Microcorys are polyphyletic, and Microcorys paraphyletic with respect to Westringia Sm. Notwithstanding that, the infrageneric classification of Hemigenia was largely supported, while in Microcorys, there was support for sect. Hemigenioides, but sects Anisandra and Microcorys were not resolved as distinct.     

An established cell line from the beetle, Xylotrechus pyrrhoderus (coleoptera: Cerambycidae)

Summary A continuous cell line has been established from larval fat body tissues of the cerambycid beetle Xylotrechus pyrrhoderus Bates. These cells were cultured in MGM-450 medium. The cell line, designated as XP-1, showed a heterogeneous population consisting of spherical and spindle-shaped cells with some capacity to adhere and a doubling time of 5 d. The chromosome number of the cell line ranged from 18 to 42 with a mode of 20. Isozyme analysis showed that the cells had patterns distinctive from those of other insect cell lines. The cells were sensitive to insect hormones, and when continuously treated with 20-hydroxyecdysone and juvenile hormone, they assumed a floating elongated-spindle shape and became strongly adherent, respectively.     

Ultrastructure of the gametes ofCoelomomyces dodgei Couch (Blastocladiales,Chytridiomycetes)

Summary As part of an investigation on the developmental biology ofCoelomomyces dodgei Couch (Blastocladiales, Chytridiomycetes), the ultrastructure of the male and female gametes was studied. The nucleus is central and conical in shape except for a basal spur that curves back towards the large plate-like mitochondrion. A nuclear cap of ribosomes sits on the flat anterior end of the nucleus. Approximately seven lipid globules are partially embedded in the mitochondrion and are interconnected by membrane cisternae. The lipid globules are covered by a single fenestrated microbody and a backing membrane lies between the microbody and the gamete plasma membrane. The kinetosome is at the base of the nucleus and is connected to a single, posterior, whiplash flagellum. A nonkinetosomal centriole is absent. In the peripheral cytoplasm of both mating types there is a paracrystalline body of unknown composition and function. No significant ultrastructural differences were found between the male and female gametes.     

Light and electron microscopical studies onHafniomonas gen. nov. (Chlorophyceae,Volvocales), a genus resemblingPyramimonas (Prasinophyceae)

Based on light and electron microscopical studies ofPyramimonas reticulata the genusPyramimonas is shown to contain a number of unrelated flagellates.P. reticulata andP. montana are transferred to the new genusHafniomonas, cells of which differ fromPyramimonas in shape, in the absence of scales and hairs on the body and flagellar surfaces, in details of the chloroplast, the position of the nucleus, the Golgi apparatus, the internal structure of the flagellar apparatus, and in cell division. The prasinophytePyramimonas contains a characteristic association of a large microbody and a rhizoplast, situated on the nuclear surface. A similar association is being found in an increasing number of prasinophycean flagellates, but is absent inHafniomonas, which is considered related to chlorophycean rather than prasinophycean flagellates. The phylogenetic position ofHafniomonas is discussed, based in particular on details of the unique flagellar apparatus.     

Morphology and ultrastructure of teratological forms of the diatoms Stephanodiscus niagarae and S. parvus (Bacillariophyceae) from Hamilton Harbour (Lake Ontario,Canada)

Teratological forms of Stephanodiscus niagarae Ehrenb. and S. parvus Stoermer & Håkansson were observed during a study of diatoms preserved in a radiometrically dated core from Hamilton Harbour (Lake Ontario, Canada). Morphological features and ultrastructures of both species were studied under the light and scanning electron microscope. The valve structure of abnormal forms of S. niagarae appears to be weakly silicified, especially in the central area. The shape of satellite pores are very irregular in comparison with the round shape of the normal specimen. The central fultoportulae are characterized as small tubes extending out of the external valve. Two types of abnormal frustules are present in the population of S. parvus studied. In one type valves are underdeveloped and only the siliceous layer and ribs are present, and in the other type the valves are strongly silicified and the areolae are almost completely occluded.The teratological forms of both species appeared in the core sediments after 1911, and both became the dominant components of diatom assemblages after 1970. Their occurrence and increased abundance coincides with records of heavy metal pollution in the harbour.     

Endogenous factors,external cues,and eccentric construction inPolistes annularis (Hymenoptera: Vespidae)

This study explores the relationship between various factors and the construction of the distinctive inclined, eccentric, and curved combs of Polistes annularis.Foundation and early construction show stereotypical inclination and bilateral symmetry. Eccentric comb shape is modestly related to inclination and highly repeatable by wasps building on combs of high inclination. Later construction by the foundresses or by their worker offspring is less stereotypical. Features associated with curvature of mature nests, such as nonhexagonal cells, are peculiar to construction by workers and occur nonrandomly, suggesting functional adaptation.     

Ultrastructure of carpospores inGastroclonium clavatum (Roth)Ardissone (Rhodymeniales)

Summary Carpospores ofG. clavatum have been studied under the light and electron microscopes. They are wedge-shaped cells of 80–100 m at their longest diameters. The nucleus is an uncondensed structure provided with a regular outline and a large nucleolus. The plastids constitute heterogeneous populations of organelles differing in size and shape as well as in number and arrangement of the thylakoids. Multiplicating plastids are also present. The mitochondria are small but have well developed cristae. The Golgi apparatus consists of very numerous active dictyosomes. Starch is the main storage substance but some large lipid bodies are also present. Labyrinthine polysaccharide aggregations are present in the carposporial cytoplasm. Multilayered bodies constitute a sui generis very conspicuous cell component.     

The ultrastructure of the sinus gland of the crayfish Astacus leptodactylus (Nordmann)

Summary An ultrastructural study of the sinus gland of the crayfish Astacus leptodactylus demonstrates that this gland is mainly composed of glial cells, axons and axon terminals. On the basis of the size, shape and electron density of the neurosecretory granules, we could distinguish five different types of axon terminals.     

Achilaophonte maxima gen.n., spec.n., a new taxon of the Laophontidae (Copepoda,harpacticoida) from the high Antartic (Weddell Sea)

Male and female of a new genus and species of the family Laophontidae, Archilaophonte maxima, are described. The specimen was found in the high Antartic (Weddell Sea) and apprears to be the most primitive genus up to now within the superfamily Laophontoidea as defined by Huys (1990). Based on its setation of legs and mouth parts, however, it can be placed unequivocally into the family Laophontidae. Archilaophonte maxima gen. n. shows close affinities to the laophontid genus Esola Edwards 1891. Both genera form a monophyletic group which is interpreted here as the first and most primitive offshot in the evolution of the Laophontidae. The synapomorphies of the former lineage are the shape of the protopodite of the P1 and shape and setation of the female P5.     

Ontogenesis of monad pollen inPterostylis plumosa (Orchidaceae,Neottioideae)

Pterostylis plumosa (Neottioideae) is an orchid with monosulcate monad pollen. Tetrads may be isobilateral, decussate, tetrahedral, rhomboid or T-shaped, but all pollen grains have a similar shape. Those belonging to the same tetrads are contiguous from microspore release to opening of the anther, with the furrow oriented inwards. Sporophytic proteins are present outside the furrow. The tapetum is of the parietal type without orbicles. The increase in pollen grain size between meiosis and maturity is only three-fold. The generative cell is spherical when the pollen is mature. These features are discussed in relation to the primitive nature of the species.