02516nas a2200169   4500008004100000020001400041245011700055210006900172260000800241300001400249490000700263520197400270100001902244700001602263700002102279856004602300       2002                        eng d  a0008-430100aUltrastructure of spermatogenesis in the free-living marine nematode Pontonema vulgare (Enoplida, Oncholaimidae)0 aUltrastructure of spermatogenesis in the freeliving marine nemat  cAug  a1371-13820 v803 aSpermatogenesis in testes of the free-living marine nematode Pontonema vulgare was studied with electron microscopy. The nucleus of spermatocytes has a large nucleolus; the cytoplasm is filled with numerous ribosomes, mitochondria, cisternae of the rough endoplasmic reticulum (RER), Golgi bodies, and flattened osmiophilic cisternae, which are interpreted as the modified membranous organelles (MO) of the spermatozoa of other nematodes studied. After completion of the second meiotic telophase, the nucleus is surrounded by a newly formed nuclear envelope. Further nucleus transformation includes condensation of the chromatin and shrinkage of the nuclear envelope. The deep infoldings of the nuclear envelope give a starlike shape to the nuclei. The cytoplasm of the early spermatids contains the same organelles as in the late spermatocytes, including MO. Many of the latter assume a cuplike or pocketlike shape. During spermatogenesis the peripheral cytoplasm containing the ribosomes, RER, Golgi bodies, and transparent vesicles moves to one pole of the cell forming the residual body. The main cell body of the late spermatid includes the nucleus, mitochondria, and MO embedded in a dense filamentous matrix. The fibrous bodies (FB) of a paracrystalline structure occur in spermatids throughout their developmental transformations. The central part of the spermatozoa contains a starlike nucleus with a nuclear envelope. The filamentous cytoplasm of the spermatozoa includes mitochondria and MO. The spermatozoa extracted from the testes form numerous long filopodia. The dense filamentous cytoplasm of the spermatozoa is continuous with the content of the filipodia. The reconstitution of the nuclear envelope and separate development of MO and FB described in P. vulgare spermatogenesis are the special characters of enoplid nematodes. The reduced character of FB development and simplified structure of MO differentiate R vulgare from other nematodes studied.1 aYushin, V., V.1 aCoomans, A.1 aMalakhov, V., V.  uhttps://nematodes.myspecies.info/node/19102483nas a2200181   4500008004100000020001400041245012900055210006900184260000800253300001200261490000700273520190200280100001902182700001602201700001702217700002102234856004602255       2002                        eng d  a0168-817000aUltrastructural study of cuticle formation during embryogenesis of the free-living marine nematode Enoplus demani (Enoplida)0 aUltrastructural study of cuticle formation during embryogenesis   cDec  a189-2030 v423 aCuticle formation during embryogenesis in the free-living marine nematode Enoplus demani (Enoplida) was studied electron microscopically. Cuticle formation begins in the three-fold loop embryo where epidermal microvilli with rounded tips are associated with the filamentous primordial cuticle. This coincides with proliferation of the cisternae of RER, Golgi bodies, multivesicular bodies and numerous transparent vesicles in the epidermal cells. In the four-fold loop embryo the epidermal microvilli are associated with the primordial cuticle, which is represented by a dense filamentous layer of uniform thickness. These microvilli are arranged into regular rows; their apical tips are flattened and filled with dense material. At pretzel I stage the space between epidermal microvilli becomes transparent and the first stratification occurs in the primordial cuticle. At pretzel 2 stage the cuticle is clearly stratified. The transparent space with longitudinally orientated fibres separates the filamentous basal layer from the dense striated cortex. A thin osmiophilic layer (epicuticle) covering the cortex appears. The number of Golgi bodies, cisternae of RER and multivesicular bodies in the epidermal cells peaks at pretzel 3 stage, the cuticle becomes much thicker and its filamentous basal layer is now distinctly stratified. The epidermal microvilli are slightly shorter than at previous stages. At pretzel 4 stage (1-2 days before hatching), the epidermal microvilli disappear at the interchordal regions. The cuticle of newly hatched first stage juveniles includes an external amorphous layer, an osmiophilic epicuticle, a striated cortex, a layer of thick longitudinal fibres and a basal layer consisting from several sublayers of different structure. Cuticle formation in nematodes is discussed in the light of the hypothesis of monophyly of the moulting invertebrates (Ecdysozoa).1 aYushin, V., V.1 aCoomans, A.1 aBorgonie, G.1 aMalakhov, V., V.  uhttps://nematodes.myspecies.info/node/19202238nas a2200169   4500008004100000020001400041245011600055210006900171300001000240490000700250520169200257100001901949700001601968700001701984700002102001856004602022       2002                        eng d  a0869-691800aUltrastructural study of the tadpole stage of the primitive marine nematode Enoplus demani (Enoplia : Enoplida)0 aUltrastructural study of the tadpole stage of the primitive mari  a43-530 v103 aThe ultrastructure of the tadpole (11/2 fold) embryo of the free-living marine nematode Enoplus demani was studied. The cells of the tadpole embryo show no distinct cyto-differentiation. Cytoplasm contains mitochondria and is filled with yolk granules and lipid droplets; nuclei contain clumps of condensed chromatin. The cells at the different stages of the mitotic cycle occur frequently in all the primordial embryonic layers. The centrosomes of the mitotic spindles include centrioles. The cells of the epidermis and the intestine form distinct layers of polarized cells underlain by basal lamina and connected at the apical ends by adherent junctions. The apical membranes of epidermal cells are slightly undulated, occasional cisternae of RER and Golgi bodies occur in the apical cytoplasm. The epidermis of the head-end forms many small funnel-shaped invaginations, interpreted here as the result of morphogenetic cell movement associated with cephalic sensilla formation. There is no distinct lumen in the tadpole intestine, rare microvilli occur squeezed between the apical membranes of intestinal cells. Presumptive muscle cells have no myofilaments, but mitochondria are abundant at the future basal (contractile) part of the cells. The pair of primordial germ cells (PGC) are positioned in the blastocoel latero-ventrally to the mid-part of the intestine. These cells are about twice the diameter of other cells of the embryo. The cytoplasm of PGC does not differ from the cytoplasm of somatic cells of the embryo, and specific P-granules are absent. Data on cell structure of E. demani tadpole embryo are compared with data on cell differentiation in Caenorhabditis elegans.1 aYushin, V., V.1 aCoomans, A.1 aBorgonie, G.1 aMalakhov, V., V.  uhttps://nematodes.myspecies.info/node/193