Organization and ultrastructure of the nervous system in Catenulida (Turbellaria)

Summary The fine structure of the nervous system of lower fresh-water Turbellaria was investigated. This system consists of a brain, short nerve trunks and a network of subepithelial nerve cells. The brain structure shows ganglion cells and their proccesses, forming a neuropil. The ganglion cells are most probably unipolar. The perikaryon contains numerous ribosomes, few mitochondria, and golgi complexes. Thus it corresponds structurally to neuroblasts of higher animals. The neurites contain mitochondria, neurotubules, and empty or dense core vesicles. All (inStenostomum sp.) or some of the nerve cells (inCatenula sp.) have neurosecretory vesicles.     

Multiple ciliary stuctures in developing spermatozoa of marine Catenulida (Turbellaria)

Summary Numerous short ciliary structures are described in immature spermatozoa of a marine catenulid,Retronectes atypica (Doe and Rieger, 1977). These ciliary structures are associated with spherical bodies consisting of concentric flat vesicles. Since such spherical bodies have been described for several other species of Retronectidae (Sterrer and Rieger, 1974), it is assumed that the multiple ciliary structures may be a characteristic of the whole family. Nuclear morphology and other cytological structures are described for mature and immature stages of spermatogenesis. The finding of these ciliary structures is thought to underline the unique and isolated position of the Catenulida within the Platyhelminthes and the lower worms as a whole.     

The nervous system of Microstomum lineare (Turbellaria,Macrostomida)

Summary The ultrastructure of release sites of neurochemical messenger substances in the microturbellarian Microstomum lineare was examined. Aminergic neurites form conventional synapses and synapse-like structures (SLS). Variants of true synapses include: single synapses with symmetric pre- and postsynaptic densities, shared synapses, i.e., contacts between 1 pre- and 2 postsynaptic fibres, en passant synapses between parallel axonal membranes, and synapses without thickenings having only clustered vesicles in the presynaptic terminal. SLS on a nerve cell soma or facing an intercellular stromal channel near muscles are described. Peptidergic neurites containing large granular vesicles (LGV) form synaptoids and signs of putative neurosecretory release. Synaptoids between neurites and between neurite and muscle have lucent vacuoles (about 100nm) and dense material at the contact site. In en passage synaptoids dense-core vesicles are embedded in electron-dense material at the contact site. Putative signs of release of neurosecretory material other than typical exocytosis have been observed.     

Ultrastructure and potential significance of cerebral light-refracting bodies of Stenostomum virginianum (Turbellaria,Catenulida)

Summary Light-refracting bodies, possibly photoreceptors, occurring in the posterior lobes of the brain are considered characteristic for most species of catenulid turbellarians of the freshwater genus Stenostomum. In S. virginianum, each of two light-refracting bodies consists of a single cup-shaped granule (3–4 m) situated in the perikaryon of a single nerve cell (the clear vesicle of earlier papers). TEM reveals each granule as an enlarged and folded mitochondrion with a dense matrix inclusion of undetermined composition. Cristae are well-developed and there is a dense granular extramito-chondrial layer of uniform thickness (100 nm) along the posteromedial surface of the mitochondrion. The perikaryon is packed with ribosomes, -glycogen granules and 60–100 nm dense-cored vesicles. A neurite extends from the perikaryon into the neuropile of the brain. Experimental data indicate an absence of phototaxis and photokinesis and an absence of ultrastructural modifications with light- and dark-adaptation. An ultrastructural comparison is made of the light-refracting bodies of S. virginianum with those of a second species. Hypotheses regarding the role of light-refracting bodies as photoperiodic receptors and/or specialized neurosecretory cells are advanced.This study was supported in part by a National Science Foundation grant DEB-7823395 and a Clemson University Faculty Research Grant to E. Ruppert     

Comparative characterization of the nervous system of the Turbellaria

Initial stages of the centralization of the nervous apparatus in the Turbellaria can be traced through a comparison of the structure of the nervous system in various representatives of the class. The most primitive state, found in the Acoela, is predominantly plexiform with a varying number of longitudinal trunks. Three, and in some cases four, longitudinal trunks are found in the Proseriata and Temnocephalida. Commissures appear in the Macrostomida and all higher orders and form an orthogon. Brain shape varies from ring-shaped in the Acoela to bilobed in the Neorhabdocoela. While the nervous system of the Polycladida is peculiar, having numerous lateral trunks and separation of dorsal and ventral parts of the nervous system, the development of the nervous system in Müller's larvae of polyclads shows it is of an orthogonal type comparable to other platyhelminths. Transition to parasitism is accompanied by some progressive transformations in the structure of the nervous system.     

Localization of monoamine-containing neurones in the nervous system ofStrophocheilus oblongus (Gastropoda)

Summary The histochemical fluorescence method of Falck and Hillarp was used to locate monoamine-containing neurones in the nervous system ofStrophocheilus, a Brazilian land snail. Green-fluorescing (catecholamines) cell bodies were found only in cerebral ganglia. Neuropiles of all ganglia contained many green-fluorescing fibers most of which appeared to enter from the periphery. Giant (up to 500 ) non-fluorescing cells were seen in most ganglia of the suboesophageal mass. Green-fluorescing fibers surrounded, and apparently ended on, their axon hillocks and proximal segments of axons. Green-fluorescing sensory cells were seen in the eyeless tentacles. Cells fluorescing yellow (5-hydroxytryptamine) or yellow fading to green on exposure to ultraviolet light were found in cerebral, visceral and right palliai ganglia. Ligature of the cardiac nerve for 24 hrs resulted in an accumulation of yellow or yellow green-fluorescing masses in axons proximal to the constriction. The distribution of monoamine-containing neurones inStrophocheilus is rather similar to that found in other pulmonate molluscs such asHelix.The authors are eager to acknowledge the constant interest of Dr. Sonia Rude while the experiments were taking place. This work was jointly supported by OAS, Capes (Brazil), U. F. R. G. S. (Brazil), and Grant No. NB 00623 (USPHS).     

Substance P immunoreactivity in sensory structures and the central and pharyngeal nervous system of Stenostomum leucops (Catenulida) and Microstomum lineare (Macrostomida)

Immunoreactivity (IR) obtained by monoclonal antibodies to substance P (SP) was studied in the asexually reproducing microturbellarians Stenostomum leucops and Microstomum lineare. The IR pattern was studied by confocal and ordinary fluorescence microscopy. In both species, IR occurs in the brain in peripheral cells, neuropilar fibres, in longitudinal cords and in the pharyngeal nervous system. The IR patterns reveal neuroanatomical details not observed with other neuroactive substances. In both species, immunopositive cells send fibers to the ciliary pits. In M. lineare, additional fibres run to more frontally located sensory structures. In S. leucops, two pharyngeal nerve rings are visualized. The pharyngeal nerve ring close to the surface associated with symmetrical immunopositive cell pairs is demonstrated for the first time, while the deeper-lying pharyngeal nerve ring has been previously demonstrated by antibodies to the molluscan cardioactive peptide FMRF-amide. Two cells with strong IR are connected by short fibres to the pharyngeal nerve ring in M. lineare. In the developing new individuals, i.e., the zooids of M. lineare, IR to SP is first revealed in nerve fibres growing out from parental lateral nerve cords towards the centre of the worm where the new brain commissure will appear. Immunopositive cells in the brain periphery and close to the developing ciliary pits appear later. Simultaneous staining by antibodies to SP and 5-HT shows that IR to SP appears later than IR to 5-HT.     

Morphodynamics of the nervous system in the regenerative processes of Convoluta convoluta (Turbellaria, Acoela)]

By means of the method for revealing cholinesterases the alterations in the nervous system of Convoluta convoluta after mechanical lesion were studied. After a transversal transection of the animal into two pieces the anterior part of the body acquired the normal form within 3-4 days; the nervous system underwent inconsiderable transformations associated with a formation of a plexus in the injured area. The posterior parts of the body regenerated slowly. During the first days disintegration of the resting parts of the nervous system was observed. Later on the diffuse cholinesterase activity suggesting the beginning of the brain formation was manifested in the wound field. Plexus strands "grow" in the caudal direction from the brain in parallel with its development. Within three weeks the nervous system of the animals which had restored their mouth opening, body shape and normal behaviour consists of the brain and plexus not arranged in nervous trunks. The reaction of the nervous system to the ablation of a part of the brain and to a continuous mechanical injury were studied. The data obtained show a high morphological lability of the nervous system of Convoluta convoluta, its ability to radical structural rearrangements.     

Geschlechtliche organisation,fortpflanzungsverhalten und ursachen der sexuellen vermehrung von Stenostomum sthenum nov. spec. (Turbellaria,Catenulida)

Certain temperatures and H-Ion concentrations are necessary for the development of male and female reproductive organs. The differentiation of the reproductive system from undifferentiated cells conforms precisely with data on other species of Stenostomum.

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Abkürzungen in den Abbildungen b Bindegewebszelle - c Cilien - cy Cytoplasma - d Darm - de Ductus ejaculatorius - dl Darmlumen - do Dotter - dr Drüsenzellen - lr Lÿckenraum - m Mundöffnung - n Nucleolus - np Nephroporus - o Ovar - p männlicher Genitalporus - pa parenchymatischer Raum - pf periembryonale Flüssigkeit - dse dorsale Epidermis - e dorsolaterale Epidermis - ed extraembryonaler Dotter - ee Epidermiseinstülpung - eh Epidermis +Hautmuskelschlauch - em Embryo - ex Exkretvakuole - f Freßzelle - g Gehirn - ga Gehirnanlagen - gr Granula - h Hautmuskelschlauch - hz Hüzllzelle - kl Versehlußkegel/Klebkegel - in indifferente Zelle - k Kern - kdr Klebdrüsenzelle(n) - kk kollabierter Kanal - kö Körnerkolbenzelle - kp Kopulationsorgan - ku Kufen - kw Körperwand - l Lichtsinnesorgan - li Linsenkörper - lk lichtbrechende Konkremente im Darmgewebe - ph Pharynx - phr Pharynxregion - pr Zentralkanal des Protonephridialsystems - ps Präspermatide - pu Punktfeld - q Zellquartett - r Riechgruben - rh Rhombuszellenband - rhb Rhabditen - rm Radiärmuskelzelle - rhs Rhabditenschleim - rs resorbierende Darmzelle(n) - s Schale - sc Spermatocyten - se Sekretgang - t Tastborste - ta Auflösungsprodukte des Hodens - te Hoden - to Terminalorgane(e) - tz Teilungszone - v Vakuole - w vermutliches Rudiment des weiblichen Genitalporus     

Immunoreactivity to a specific echinoderm neuropeptide in the nervous system of the flatworm Macrostomum hystricinum marinum (Turbellaria,Macrostomida)

Immunocytochemical characterization of the neuropeptides FMRF-amide and serotonin (5-HT) is a well-known method successfully applied to demonstrate nervous-system morphology in several platyhelminths (see Wikgren & Reuter, 1985, and Reuter, 1988, for review). We have immunolabeled whole-mount preparations of Macrostomum hystricinum marinum Rieger from cultures (see Rieger et al., 1988) with anti-SALMF-amide, an antibody specific for the C-terminal pentapeptide sequence of the neuropeptide GNFSALMF-amide recently isolated from echinoderms (source M. Thorndyke, England). Immunoreactivity to SALMF-amide gave a more detailed picture of the nervous system of M. hystricinum than FMRF-amide. Conventional light microscopy (Luther, 1905) shows this nervous system to consist of a bilobed brain, a pharyngeal nerve-ring system, a posterior commissure, and two main ventrolateral nerve cords. Immunostaining reveals, in addition, two thin paired longitudinal nerve strands and fine subepithelial and submuscular nerve nets. Anti-SALMF-amide labels a distinct class of neurons, causing the main lateral longitudinal cords and pharyngeal nerve-ring system to appear more filamentous than with other techniques. Recent fine-structural investigations on the nervous system of Macrostomum hystricinum marinum revealed several axon types with characteristic vesicles and neurotubules (D. R. pers. obs.). Partly supported by FWF grant P7816.     

Localization of cholecystokinin-like immunoreactivity in the central nervous system of Triatoma infestans (Insecta: Heteroptera)

The distribution of cholecystokinin-like immunoreactivity was studied in the central nervous system of the heteropteran insect Triatoma infestans using high-sensitivity immunocytochemistry. In the protocerebrum, CCK-IR somata were observed in the anteromedial, anterolateral and posterior cell-body layers. The neuropils displayed different densities of immunoreactive neurites. Few immunoreactive somata were found in the optic lobe in both the medial and lateral soma rinds, as well as in the proximal optic lobe. Immunoreactive fibers were present in the medulla and lobula neuropils. The sensory deutocerebrum contained a higher number of immunopositive perikarya than the antennal mechanosensory and motor center. The antennal lobe glomeruli displayed a moderate density of immunoreactive fibers. With regard to the subesophageal ganglion, numerous CCK-IR somata were found close to the root of the mandibular nerve; others were present in the soma rind of the remaining neuromeres. CCK-IR perikarya were present in both thoracic ganglia, with the abdominal neuromeres containing the highest number of positive somata. The neuropils of both ganglia showed moderate densities of immunopositive processes. The distribution of CCK-LI in somata and neuropils of central nervous system of T. infestans is widespread suggesting that a CCK-like peptide may act mainly as a neuromodulator in the integration of information from distinct sensory receptors.     

Localization and distribution of catecholaminergic structures in the nervous system of Phocanema decipiens (nematoda)

The nervous system of Phocanema decipiens was examined with both the formaldeyhyde-induced and the glyoxylic acid fluorescence histochemical techniques. Green catecholaminergic structures were observed in 4 cephalic papillary nerves, 2 fibres with varicosities in the nerve ring as well as the ventral nerve cord and a pair of lateral nerves.The papillary nerves, extending from the nerve ring to the lips region, have cell bodies which are located anterior or adjacent to the nerve ring. Cell bodies of the lateral nerves are found within the lateral cord tissue posterior to the nerve ring. Each of these neurons has 3 processes—one joins with the nerve ring, the other merges with the ventral nerve cord and the third ends abruptly within the lateral cord.     

The organization of the nervous system in Plathelminthes. The neuropeptide F-immunoreactive pattern in Catenulida,Macrostomida, Proseriata

The organization of the nervous system of Archilopsis unipunctata Promonotus schultzei and Paramonotus hamatus (Monocelididae, Proseriata) and Stenostomum leucops (Catenulida) and Microstomum lineare (Macrostomida) was studied by immunocytochemistry, using antibodies to the authentic flatworm neuropeptide F (NPF) (Moniezia expansa). The organization of the nervous system of the Monocelididae was compared to that of the nervous system of Bothriomolus balticus (Otoplanidae), a previously studied species of another family of the Proseriata. The results show that the main nerve cords (MCs), independent of lateral or ventral position in the Monocelididae and the Otoplanidae, correspond to each other. The study also confirms the status of the lateral cords as main cords (MCs) in S. leucops and M. lineare. Common for MCs in the members of the investigated taxa are the following features: MCs consist of many fibres, originate from the brain and are adjoined to 5-HT-positive neurons. In Monocelididae and Otoplanidae, the MCs additionally have the same type of contact to the pharyngeal nervous system. Also common for both proseriate families is the organization of the two lateral nerve cords, with weaker connections to the brain, and the pair of dorsal cords running above the brain. The organization of the minor cords differs. The Monocelididae have a pair of thin ventral cords forming a mirror image of the dorsal pair. Furthermore, an unpaired ventral medial cord connecting medial commissural cells was observed in P. schultzei. Marginal nerve cords, observed in Otoplanidae, are absent in Monocelididae. All minor nerve cords are closely connected to the peripheral nerve plexus. The postulated trends of condensation of plexal fibres to cords and/or the flexibility of the peripheral nerve plexus are discussed. In addition, the immunoreactivity (IR) pattern of NPF was compared to the IR patterns of the neuropeptide RFamide and the indoleamine, 5-HT (serotonin). Significant differences between the distribution of IR to NPF and to 5-HT occur. 5-HT-IR dominates in the submuscular and subepidermal plexuses. In the stomatogastric plexus of M. lineare, only peptidergic IR is observed in the intestinal nerve net. The distribution of NPF-IR in fibres and cells of the intestinal wall in M. lineare indicates a regulatory function for this peptide in the gut, while a relationship with ciliary and muscular locomotion is suggested for the 5-HT-IR occurring in the subepidermal and submuscular nerve, plexuses. In M. lineare, the study revealed an NPF- and RFamide-positive cell pair, marking the finished development of new zooids. This finding indicates that constancy of these cells is maintained in this asexually reproducing and regenerating species.     

Revision of Koinocystididae (Turbellaria)

The revision deals with the anatomy and systematics of the known 38 species of Koinocystididae. The taxonomy within the family is revised, a key for the identification of live specimens is given and an attempt is made to reconstruct the phylogeny of genera and species on the basis of anatomical transformation series. New genera are Axiutelga. Brunetia, Getula. Groveia, Itaipusina, Legula ana Neoutelga. New species are Groveia unicornis, Itaipusa bispina, I. curvicirra, Neoutelga inermis, Rhinolasius dillonicus and Utelga pseudoheinckei from the N. American Pacific coast (the latter species also from European coasts) and Itaipusina graefei from the Elbe estuary. Acrumena massiliensis Brunet is transferred from Koinocystididae to Acrumenidae fam.n. Four species are considered to be species incertae sedis.