Unique patterns of longitudinal body-wall musculature in the Acoela (Plathelminthes): the ventral musculature of Convolutriloba longifissura

The ventral musculature of Convolutriloba longifissura (Acoela) has been studied using electron microscopy and fluorescently labeled whole mounts to demonstrate filamentous actin. Attention was directed to the reorganization and renewal of musculature during asexual reproduction and the adaptation of muscle sets for special predatory behavior. Three ventral subepidermal muscle layers could be distinguished in adult C. longifissura: (1) outer circular muscles that encircle the body, (2) intermediate modified longitudinal muscles with concentric pattern around the mouth and V-shaped orientation in the posterior part of the animal, and (3) inner special pore muscles with radial alignment fanning out from the mouth. Additionally, a few very fragile muscles were found at the anterior margin of the animal. The anterior ventral muscle system built a funnel with the mouth opening as organizing center. The special radial muscles and the antagonistically concentric muscles are perfectly adapted to catch prey in such a way that the funnel is put over the prey to press it through the mouth into the digestive syncytium. Convolutriloba longifissura shows a unique way of asexual reproduction by a two-step fission which results in three individuals. Immediately after separation from the mother animal, daughter individuals are missing the concentric and the radial muscle sets around the mouth completely, but within 30 h these sets are renewed for the most part. Two to three days after separation, the mouth opening is visible and the animals move for capturing prey. The peculiar course of longitudinal muscles in C. longifissura with concentric rings anteriorly and a V-shape muscle layer posteriorly shows that the pattern of body-wall musculature in such basal Plathelminthes as the Acoela may be highly modified from the original pattern of longitudinal and circular muscles.     

Egg capsules of a parasitic turbellarian flatworm: ultrastructure of hatching sutures

Egg capsules of Syndisyrinx franciscanus, an intestinal parasite of sea urchins (Strongylocentrotus spp.), consist of a bulb, which contains the embryos, and a stalk-like filament. The wall of the bulb is about 12 microns thick and is composed of sclerotized proteins. The end of the bulb opposite the attachment of the filament bears a reticulum of hatching sutures. Transmission electron microscopy discloses that hatching sutures traverse the entire thickness of the capsule wall. The inner 9-10 microns of sutures are a uniform 20 nm in width and contain a trilaminar cementum. The outer 2-3 microns of sutures are 15 nm to more than 500 nm in width and contain an electron-lucent cementum. The latter may contain an irregular, median, electron-dense layer or, more commonly, electron-dense granules. The outside of some capsules is partially covered by a thin, electron-dense material. A previous study showed that sutures in intact capsules of Syndisyrinx franciscanus are not affected by host digestive fluids, but are severely weakened immediately prior to hatching owing to activities of the embryos. The hypothesis that the embryos secrete a hatching enzyme is supported by findings that sutures of intact capsules are not affected by externally applied trypsin, but become weakened when capsules are cut open and then incubated in trypsin. Scanning electron microscopy reveals that the outer parts of sutures often remain intact after hatching. We hypothesize that the ability of sutures to resist enzymatic attack from the outside, but not the inside, results from differences in the chemical properties of the cementums in outer and inner parts of sutures.     

Lipid biosynthesis in the marine flatworm Convoluta roscoffensis and its algal symbiont Platymonas convoluta.

As a part of an investigations on the lipid metabolism in Platyhelminthes, the acoel Convoluta roscoffensis, which harbors the green alga Platymonas convoluta as a symbiont, was studied. Isotopic tracer experiments established that the acoel lacks the ability to synthesize de novo long-chain saturated and unsaturated fatty acids and depends on its algal symbiont for these compounds. The acoel's fatty acid composition closely resembles that of the alga but differs from those of other animals; the acoel's polyunsaturated fatty acids are of the plant type (omega 3 family) rather than of the animal type (omega 6 family). The acoel also lacks the ability to synthesize sterols de novo. It contains 24-methylenecholesterol synthesized by the algae and, in addition, significant amounts of cholesterol, which is probably a host modification product of the algal sterol. With fatty acids provided by the symbiont, the acoel has the ability to synthesize its own complex lipids. The acoel contains relatively large amounts of triglyceride, phosphatidylcholine, and ethanolamine plasmalogen. These compounds are either not present at all or present only in minute amounts in the symbiotic alga. Since acoels belong to the most primitive forms of the present-day flatworms, the observed metabolic defects in this organism suggest that mechanisms for the biosynthesis of fatty acids and sterols were lost early during the evolution of the Platyhelminthes, and that this phenomenon is widespread within the phylum.     

On the histology and ultrastructure of the Harderian gland in rabbits

Summary The Harderian gland of rabbits has been studied with light and electron microscopes. The red part contains relatively wide alveoli with an irregular cuboidal epithelium. The stainability of the cytoplasm is poor. The white part has smaller alveoli with a low columnar epithelium. The cells show cytoplasmic basophilia removable with ribonuclease. The cytoplasm of both kinds of cells is very dense when examined in the electron microscope. The mitochondria show branched, closely packed cristae and a dense matrix. The Golgi apparatus displays few lamellae and rows of vacuoles. The endoplasmic reticulum is very finemeshed and partly associated with ribonucleoprotein particles. Both kinds of cells contain numerous lipid droplets, leaving vacuoles in the sections prepared for electron microscopy. They are fewer but distinctly larger in the red part. In both lobes pictures suggesting a secretion of lipid droplets have been observed. Cells showing signs of degeneration with subsequent discharge of the detritus have been observed in both lobes, but this process does not correspond to the holocrine secretion in sebaceous glands. Likewise, no apocrine secretion was observed.     

Effect of hexachlorobenzene and acetone on algal growth: physiology and ultrastructure

The effect of hexachlorobenzene (HCB) and acetone on growth and ultrastructure of the freshwater alga Chlorella pyrenoidosa was studied. The algal cells were grown for 76 h under continuous light in 10 ppm HCB with 0.33% acetone or in 0.33% acetone alone; the control cells were grown in nutrient solution only. As was deduced from determinations of dry matter, carbohydrates, chlorophyll content and total nitrogen, 0.33% acetone in nutrient solution slightly decreased the growth of the cells without having any influence on their ultrastructure while 3.33% acetone affected the ultrastructure of the cells severely. An incubation of Chlorella with 10 ppm HCB in nutrient sultion containing 0.33% acetone led to a drastic decrease of all growth parameters studied, total nitrogen and chlorophyll content being affected most strongly. These latter observations were in accord with the changes in ultrastructure showing damage to the cell membranes, disintegrated cytoplasm and sometimes even break down of cell organells leaving only starch grains, the pyrenoid and some endomembranes. In addition to these cells with severe lesions, quite normal cells were found.     

The ultrastructure of neuromuscular systems in Notoplana acticola,a free-living polyclad flatworm

Summary Neuromuscular junctions in the marine polyclad flatworm, Notoplana acticola were studied with the electron microscope. Synapses were found between nerve endings and specialized extensions of the muscle cells. Characteristically these processes contained clear cytoplasm with a basal mitochondrion and numerous microtubules aligned parallel to the long axis of the extension. Sarcoplasmic diverticuli which contained the nucleus had granular cytoplasm with an assortment of membranes and organelles. We have proposed the term sarconeural junction to describe synapses between long sarcoplasmic extensions and nerve cells in flatworms as well as other animals.Tight junctions between adjacent contractile portions of muscle cells were common. As groups of cells appeared to be connected by tight junctions or shared common nerve terminals we conjectured that these formed discrete functional motor-units.     

A freeze-etch study of the ultrastructure of red algal pit plugs

Summary Freeze-etch studies indicate that the fully-formed pit plug ofPalmaria palmata consists of a homogeneous plug core, a pair of plug caps, and associated membranes. A single cap membrane separates the two layers of each plug cap and is the only membrane found between the cytoplasm and the plug core. Due to the apparent junction of the plasmalemma and cap membranes, the plug core, along with the adjacent plug cap layer on either face of the core, is entirely membrane-bounded and essentially extracellular. Fracture faces of the cap membrane bear large populations of particles which are inconspicuous due to their low profile. The plasmalemma lining the plug core from cell to cell has numerous, very obvious particles on its fracture faces, more even than does the cytoplasmic plasmalemma.The relationship of the rhodophycean pit plug to the fungal septal pore plug is discussed.This report represents a portion of a thesis submitted in partial fulfillment of the requirements of a Master of Science degree, Cornell University, Ithaca, N.Y.     

The histology and ultrastructure of the salivary glands of Neopanorpa longiprocessa (Mecoptera: Panorpidae)

The salivary glands of Panorpidae usually exhibit distinct sexual dimorphism and are closely related to the nuptial feeding behavior. In this study, the salivary glands of Neopanorpa longiprocessa were investigated using light microscopy and transmission electron microscopy. The salivary glands are tubular labial glands and consist of a scoop-shaped salivary pump, a common salivary duct, and a pair of salivary tubes. The male and female salivary glands are remarkably different in the bifurcation position of the common salivary duct and the length and shape of the secretory tubes. Compared with the simple female salivary glands, the male’s are more developed as their paired elongated salivary tubes can be divided into two parts, the glabrate anterior tube and the posterior tube with many secretory tubules. The ultrastructural study shows that the male salivary tubes have strong secretory function. The existence of different secretion granules indicates that there are some chemical reactions or mixing occurring in the lumen. Based on the ultrastructural characteristics, the functions of the different regions of the salivary tube have been speculated. The relationship between the salivary glands and nuptial feeding behavior of N. longiprocessa has been briefly discussed based on the structure of the salivary glands.

     

The marine algal flora of Angola: its distribution and affinities

Angola has previously received little attention from marine phycologists. Thirty known papers mention marine macro-algae and together list less than 50 species. This paper deals with the results of a survey carried out during January and February 1974: the number of reported species is now more than doubled. The species characterizing the littoral zones of rocky shores in this country are largely also to be found along the Guinea Coast, although minor variations do occur. The affinities of the Angolan marine algal flora are overwhelmingly with the Gulf of Guinea flora; there is a small but distinct transitional element, such as Plocamium beckeri, P. suhrii and Acrosorium maculatum , confined to localities in the south of Angola.     

Benthic algal biomass in an unshaded first-order lowland stream: distribution and regulation

The vertical distribution of algal biomass in the bed sediment and the seasonal development of benthic algae on stones and fine-grained sediments were studied in a small unshaded stream. In addition, field experiments were conducted on the role of irradiance and phosphorus in regulating algal biomass. We found that algal biomass was high at a sediment depth of ten centimetres. Comparison of studies on algal biomass where different depths of the sediment are used should therefore be made with caution. Substrata-dependent differences in algal biomass development were substantial. While algal biomass development on stones was controlled by macroinvertebrate grazing, that on the fine-grained sediment followed the dynamics of incident irradiance, but was attenuated by sediment rebedding. Because of the high grazing pressure on algal biomass on stony substrata, no significant response to phosphorus enrichment was attained. In contrast, algal biomass development on fine-grained sediments was phosphorus-limited. Heavy shading of the fine-grained sediments did not significantly affect algal biomass development, thus suggesting that phosphorus limitation prevents algae from fully utilizing the light resource in this stream. This revised version was published online in July 2006 with corrections to the Cover Date.     

Artichoke latent virus: characterisation, ultrastructure and geographical distribution

An isolate of artichoke latent virus (ALV-I) obtained from a symptomless artichoke plant in Southern Italy was characterised and compared with ALV isolates from other countries. ALV occurs in California and throughout the western part of the Mediterranean basin but of Mediterranean countries east of Italy, it was found only in Israel and Turkey. ALV-I was readily transmissible by inoculation of sap to a moderate range of hosts, was transmitted in a non-persistent manner by Aphis fabae, Brachicaudus cardui and Myzus persicae, but was not seed transmitted. The virus has flexuous rod-shaped particles measuring c. 12 nm × 746 nm with a sedimentation coefficient of 145 S and a buoyant density of 1·31 g/cm³. The particles contain single stranded RNA with a mol. wt of 3 × 10⁶ and protein composed of a single polypeptide species with a mol. wt of 33 000. Cylindrical cytoplasmic inclusions consisting of pinwheels and laminated aggregates were present in cells of naturally and artificially infected plants. ALV isolates from different geographical origin were indistinguishable from ALV-I biologically, morphologically, serologically and ultrastructurally. These properties place ALV in the Potyvirus group, but it was serologically unrelated to 12 other potyviruses 10 of which occur commonly in Italy.     

The histology and ultrastructure of the liver of Atlantic croaker Micropogon undulatus L.

Atlantic croaker, Micropogon undulatus L., were sampled from an estuary and selected offshore sites in the Gulf of Mexico. Liver samples were collected for light and transmission electron microscopy. Histologically, the Atlantic croaker liver parenchyma was arranged in tubular units. The tubules were similar to those of the primitive marine hagfish but contained unique features such as a central sinusoid and intercellular bile canaliculi. This liver structure may represent an evolutionary step from the primitive tubular hagfish liver to the muralium pattern of higher vertebrates. Pigments which may have occurred from disturbances in the normal oxidative pathways of hepatic lipids were also present in the liver.     

Ultrastructural study of oogenesis in the acoel turbellarian Convoluta

An ultrastructural investigation of oogenesis has been carried out on the acoel turbellarian Convoluta psammophyla. Developing female germ cells are not contained in well delimited ovaries but are freely distributed in the parenchyma and are surrounded by narrow cytoplasmic projections of accessory-follicle cells. Oogenesis can be divided into two periods, the previtellogenic and the vitellogenic phase. In the first period the oocyte undergoes a number of cell differentiations necessary for the intense biosynthetic activity of the second period. The ample development of nucleolus, ribosomes, endoplasmic reticulum and Golgi complexes along with the appearance of large lipid droplets and clusters of electron dense granules characterize the previtellogenic phase. The formation of yolk globules is the main feature of the second period of oogenesis. It occurs by an autosynthetic mechanism involving endoplasmic reticulum and Golgi complexes, since no endocytotic activity has been detected in the developing oocyte. The electron dense granules apparently move towards the cortical ooplasm during the late vitellogenic phase and take part in egg covering formation. Hypotheses on the role of follicle cells and on the phylogenetic significance of a comparative analysis of egg inclusions with homologous structures of other Turbellaria are suggested.     

A new viviparous acoel Childia vivipara sp. nov. with observations on the developing embryos, sperm ultrastructure, body wall and stylet musculatures

A free‐living viviparous acoel, Childia vivipara sp. nov., from the Gullmar fjord of the Swedish coast is described. The new species is assigned to the taxon Childia based on histological, ultrastructural and molecular sequence similarities. All available molecular markers (18S rRNA, 28S rRNA and histone H3) and several morphological characters, obtained using transmission electron microscopy and confocal scanning laser microscopy of whole mount specimen stained with TRITC‐labelled phalloidin, support the placement of C. vivipara in the taxon Childia. Childia vivipara and other Childia species share the following morphological synapomorphies: well‐developed copulatory organs built of tightly packed stylet needles, proximal part of the stylet inserted into the seminal vesicle, reversed body‐wall musculature, absence of ventral diagonal muscles, presence of dorsal diagonal muscles, and presence of ventral straight longitudinal muscles between frontal pore and mouth, 9 + 1 sperm axoneme structure, six distal sperm cytoplasmic microtubules, and extensive overlap of axonemes and nucleus. The new species can be easily distinguished from other Childia species by its viviparous mode of reproduction and single curved stylet. Observations on late embryonic development based on the oldest developing embryos are discussed.     

饮用水处理流程中的微藻及其去除率

为了解某市饮用水处理流程中的藻类状况,对某市饮用水源及自来水厂各主要处理过程中的水样进行藻类检测鉴定。在各水样中共检测到藻类72种,蓝藻、绿藻和硅藻为优势藻群,并检出微囊藻、颤藻和鱼腥藻等潜在产毒的种类,其中微囊藻在源水中的细胞密度为1.9×106cell·L-1。源水中藻类细胞密度为2.8×106cell·L-1,处理后自来水中藻类的细胞密度为4.6×104cell·L-1,藻类总去除率为98.3%,其中滤池对藻类的去除率为82.7%,但其对蓝藻的去除率仅为11.8%。研究结果表明,该市水源可能已受到藻毒素的污染;现有自来水处理工艺中的滤池难以对个体较小的有毒蓝藻有效去除。针对该地区水源藻类的分布情况提出了优化过滤工艺的建议。     

Epidermal ultrastructure of Anoplodium stichopi (Plathelminthes,Dalyellioida), a flatworm endosymbiotic in Stichopus tremulus (Holothurioida)

Summary The epidermal ultrastructure of Anoplodium stichopi Bock 1925 (Platyhelminthes, Dalyellioida, Umagillidae) was studied using transmission and scanning electron microscopy. The species lives in the perivisceral coelom of the aspidochirote holothurian Stichopus tremulus Gunnerus 1767. Two types of cells were observed in the epidermis of A. stichopi: ciliated cuboidal epithelial cells and nonciliated pear-shaped cells. The surface of the ciliated epidermal cells is folded into anastomosing ridges. Numerous coated vesicles are subjacent to the surface folds and mitochondria are abundant just below them. Observations indicate that A. stichopi takes up nutrients pinocytically from the coelomic fluid of the host. The ciliation of A. stichopi is sparse.     

The harderian gland of the frog, Rana esculenta, during the annual cycle: histology, histochemistry and ultrastructure

The Harderian gland in Rana esculenta has been studied during the annual cycle at the histological, histochemical and ultrastructural levels. The Harderian gland has an acinar structure and is the only orbital gland in anuran amphibia. It develops at the medial corner of the orbit from the conjunctival epithelium at the premetamorphic stage. In the adult the glandular secretion reaches a maximum during the months of July and August, drops in September and resumes slowly from October onwards. The secretion is seromucoid and the secretory granules are released into the acinar lumen, mainly by exocytosis. Porphyrins were not detected. No sexual dimorphism was observed in the glandular cells. The resumption of secretory activity in October and the enhancement of secretion in May are marked by the appearance of "blue nuclei" (Mallory stain) in a relatively high percentage of glandular cells. This unusual blue colour, using the Mallory stain (by which nuclei stain red), disappears after digestion of paraffin sections with RNAase, but not with DNAase and trypsin. The blue staining may, therefore, indicate an increased amount of nuclear RNA. The Harderian gland in the frog most probably serves to lubricate and moisten the eye in the absence of the lacrimal gland. However, the gland may also represent an immunoactive organ owing to the presence of numerous mast cells and plasma cells in the interacinar spaces.     

Analysis of the self-shading effect on algal vertical distribution in natural waters

Self-shading of light by algae growing in a column of water plays an important role in the dynamics of algal blooms. Thus without self-shading the algal concentration would increase more rapidly, making the nutrient limitation too strong. Apart from the practical importance of self-shading, its inherent nonlinearity in the growth dynamics leads to an interesting mathematical problem, which warrants detailed analytical investigation. Our mathematical model for the self-shading effect includes vertical diffusion, algal settling, gross production, and collective losses of algae. Steady-state solutions of the model equation are investigated in detail by the phase plane method, and their stability examined. Finally we discuss the vertical profile of algal concentration.Contribution No. 291 of the Marine Sciences Research Center