Ultrastructure of the area of procerebrum cell bodies in snails and slugs

Ultrastructure of the main neural elements in the cell body area of procerebrums, the higher olfactory centers of terrestrial snails and slugs, was studied. It has been shown that nearly every neuron of the procerebrums contains several types of agranular and granular vesicles used in various interneuronal connections. Several types of classic and non-classic synaptic junctions between granular cell bodies and their main processes as well as between granular cells and various neural fibers coming to this area from other brain regions are described. About 70% of the synapses and synaptic-like junctions are symmetric. Complex synaptic complexes of both divergent and convergent types are observed. It has been established that the coming fibers form numerous, spatially separated, parallel, divergent and partially overlapping, synaptic complexes with the procerebrum neurons clustered in columns. Due to the high degree of convergence of afferent inputs in the procerebrums and the huge amount of symmetric and unidirectional links, procerebrums may represent an integral, highly differentiated, integrative system of the molluscan brain.     

The darting game in snails and slugs

Love darts are hard 'needles' that many snails and slugs use to pierce their partner during mating. In a few species, darts have been shown to play a role in sperm competition. Two new papers, by Davison et al., and Koene and Schulenburg, might further pique researchers' interest, because they show how the full potential of darts can be tapped for studies of sexual selection in hermaphrodites.     

Ultrastructure of the different zones of the tectorial membrane

The tectorial membrane (t.m.) of mammals, which lies over the organ of Corti, is made up of an agglomerate of protofibrils of varying degrees of hydration. Two types of protofibrils are clearly distinguishable in the mouse t.m. While type-A protofibrils are straight and unbranched (thickness: 110A) demonstrating a periodic structure (period = 70 A), type-B protofibrils are branched and coiled (thickness: 150-200 A). These protofibrils could be systematically ordered according to the different t.m. zones. Type-A protofibrils predominate in the basal layer and in the entire middle zone, where they are interlaced with strongly hydrated type-B protofibrils. Weakly hydrated type-B protofibrils essentially make up the marginal zone (with the marginal net), the covering net, Hensen's stripe and the immediate contact layer with the limbus.     

Patterns of introduction of non-indigenous non-marine snails and slugs in the Hawaiian Islands

The native snails of the Hawaiian Islands are disappearing. One cause is predation by introduced carnivorous snails. Habitat destruction/modification is also important, facilitating the spread of other non-indigenous snails and slugs. Eighty-one species of snails and slugs are recorded as having been introduced. Thirty-three are established: 12 freshwater, 21 terrestrial. Two or three species arrived before western discovery of the islands (1778). During the nineteenth century about one species per decade, on average, was introduced. The rate rose to about four per decade during the twentieth century, with the exception of an especially large number introduced in the 1950s as putative biocontrol agents against the giant African snail, Achatina fulica. The geographical origins of these introductions reflect changing patterns of commerce and travel. Early arrivals were generally Pacific or Pacific rim species. Increasing trade and tourism with the USA, following its annexation of Hawaii, led to an increasing proportion of American species. More general facilitation of travel and commerce later in the twentieth century led to a significant number of European species being introduced. African species dominated the 1950s biological control introductions. The process continues and is just part of the homogenization of the unique faunas of tropical Pacific islands.     

Behavioural avoidance by slugs and snails of the parasitic nematode Phasmarhabditis hermaphrodita

The nematode Phasmarhabditis hermaphrodita has been developed as a biological control agent for slugs and snails. Slugs avoid areas where P. hermaphrodita is present. We investigated whether behavioural avoidance of P. hermaphrodita is a common feature of slugs and snails by exposing eight species to P. hermaphrodita. We showed that slugs generally avoided P. hermaphrodita, whereas snails did not. We also showed that slugs specifically avoided the commercial strain and a natural isolate of P. hermaphrodita and were not deterred by other nematodes such as Steinernema kraussei or Turbatrix aceti. We also showed that slugs avoided the dauer stage of P. hermaphrodita and not mixed-stage cultures. Furthermore, slugs do not avoid dead P. hermaphrodita or exudates from live nematodes. Taken together, we have unravelled further factors that are essential for slugs to avoid P. hermaphrodita in soil, which could have important implications for the biological control of slugs and snails.     

Turning snails into slugs: induced body plan changes and formation of an internal shell

The archetypal body plan of conchiferan molluscs is characterized by an external calcareous shell, though internalization of shells has evolved independently in a number of molluscan clades, including gastropod families. In gastropods, the developmental process of torsion is regarded as a hallmark that is associated with a new anatomical configuration. This configuration is present in extant prosobranch gastropod species, which predominantly bear external shells. Here, we show that short-term exposure to platinum during development uncouples at least two of the processes associated with torsion of the freshwater snail Marisa cornuarietis. That is, the anus of the treated snails is located anteriorly, but the gill and the designated mantle tissue remains in a posterior location, thus preventing the formation of an external shell. In contrast to the prosobranchian archetype, platinum treatment results in the formation of a posterior gill and a cone-shaped internal shell, which persists across the lifetime. This first finding of artificially induced snail-slug conversion was also seen in the pulmonate snail Planorbarius corneus and demonstrates that selective alteration of embryonic key processes can result in fundamental changes of an existing body plan and-if altered regulation is inherited-may give rise to a new one.     

Assimilation efficiencies of slugs on different food materials

Summary The relative assimilation efficiencies of two common British species of slug, Limax flavus (L.) and Arion hortensis (Fér.), were studied in the laboratory using a gravimetric method. Results are given for adult slugs feeding on carrot root and potato tuber at 5°, 10°, 15°, and 20° C, and for L. flavus juveniles of known age feeding on potato at 10° and 15° C. A few results are also provided for Agriolimax reticulatus (Müller) feeding on both potato and carrot at 15° C.High mean assimilation efficiencies of 76.94 and 76.87% were obtained for L. flavus feeding on carrot and potato respectively. The equivalent results for A. hortensis were 88.60 and 89.42%. For A. reticulatus at 15° C the figures were 76.1 and 71.9%. Ingestion rates and assimilation rates are given for the first two species at all temperatures. Assimilation efficiency was found to be independent of temperature for L. flavus but not for A. hortensis. Ingestion rate and assimilation rate were temperature dependent in all cases except for A. hortensis feeding on potato.A. hortensis was more efficient at consuming both carrot and potato per gram live weight. All species consumed more potato than carrot per gram live weight.Juvenile L. flavus were found to have higher assimilation efficiencies and ingestion rates than the adults per gram live weight.Linear regression equations were determined from the relationship between dry weight of food consumed, and dry weight of faeces produced from that food for L. flavus.It is concluded that food quality and age of slug may be the factors most strongly influencing assimilation efficiency in this group.     

Serotonin-stimulated biochemical events in the procerebrum ofLimax

1. The procerebrum (PC) of the terrestrial slug Limax maximus is of interest as a potential site of olfactory information processing (Gelperin et al., 1989). The neuromodulator serotonin is present in the procerebrum and can elicit action potentials from cultured procerebral neurons. We have investigated the effects of serotonin on second-messenger signaling systems and protein phosphorylation as a prelude to studies on long-term synaptic plasticity in the Limax procerebral lobe. 2. We found that several biochemical changes are triggered within 20 min of adding serotonin to the isolated procerebral lobe: adenylate cyclase is activated, protein phosphorylation and synthesis are modulated, and phosphatidylinositol-metabolism is stimulated. 3. Serotonin causes a rapid synthesis of cAMP, reaching a 20- to 30-fold increase within 1 min. Serotonin affects the rate of phosphorylation of several proteins, detected after a brief (20-min) incubation of the procerebral lobe in [32P]phosphate-containing medium. The level of synthesis of several proteins is altered by serotonin, as determined by alterations in [35S]methionine incorporation during a 20-min incubation. Serotonin also causes a slow accumulation of inositoltrisphosphate. 4. Our study shows that within a short time (less than 20 min) serotonin can influence several second-messenger signaling systems and the functional state and abundance of proteins in the procerebral lobe. These serotonin-stimulated events should have direct consequences for intercellular communication in the odor-processing network of the procerebral lobe.     

Comparative study of nerve elements and their relationships with Endocrine glands and muscle retractors in Ommatophores of snails and slugs

A comparative study of the total cytoarchitectonics and structural interrelations of receptor and nerve elements at the area of receptor cell bodies, in tentacular ganglia and their digital outgrowths as well as in the lateral wall of tentacular olfactory organs of several species of terrestrial snails and slugs from different families was carried out using Golgi and Colonnier silver nitrate impregnation technique and horseradish peroxidase labeling. The presence of a peculiar cluster of intraepithelial receptor cells has been established for the first time in sensory epithelium of ommatophores. A connection of endocrine cells of the optic gland with nerve and receptor elements of tentacular ganglia was shown. Peculiarities of innervation of muscle refractors and lateral wall of ommatophores were revealed. FMRFamide-positive nerve fibers were found to participate in innervation of muscle elements of ommatophores. Neurotensin-positive and occasional serotonin-positive nerve elements also were revealed in the tentacular organs. Electron microscopic study showed the presence of complicated synaptic complexes of either convergent or divergent type and of many symmetric synaptic structures in neuropil of tentacular ganglia. Many nervous fibers and synapses contain several types of granular and agranular vesicles, which indicates possible co-localization of several bioactive substances in the same nerve elements.Translated from Zhurnal Evolyutsionnoi Biokhimii i Fiziologii, Vol. 40, No. 6, 2004, pp. 556–568.     

The growth of juvenile snails in water conditioned by snails of a different species

Summary Two species of freshwater snails, Physa acuta and Lymnaea sp. aff. columella, were collected from Asabata marsh, Shizuoka Japan. Individuals of both species inhabit the same plants. Individuals of P. acuta are more abundant than those of L. sp. aff. columella. Experiments were conducted to examine the effect of water conditioned by snails on the growth of 10-day-old juvenile P. acuta snails. Juvenile snails in water conditioned by L. sp. aff. columella grew faster than those in water conditioned by P. acuta or only lettuce. The effects of water conditioned by P. acuta differed among the litters. The results suggest that juvenile P. acuta snails experience accelated growth in the presence of L. sp. aff. columella. The freshwater snails interacted through resource competition as well as through substances disolved in the water.     

Ultrastructure of the sympathetic paravertebral ganglia in rat embryogenesis. II. The development of the neuropil and the interneuronal connections

Electron microscopy was used to study the process of ingrowth of nerve terminals in the primordia of sympathetic ganglia and the formation of specialized contacts. Nerve terminals appeared first in 12 day old embryos. In the forming ganglia of 13 day old embryos there are many preganglionic nerve terminals and processes of principal neuroblasts. The growth cones of nerve endings are usually distended and with transparent cytoplasm. The plasmalemmas of growth cones are lacking often the trilaminar structure. Synapses were observed first in 16 day old fetuses. They are axo-dendritic and axo-somatic ones. The number of synaptic contacts does not increase much during prenatal period. Presumptive afferent nerve terminals were found in the late fetuses.     

Crawling through time: Transition of snails to slugs dating back to the Paleozoic, based on mitochondrial phylogenomics

Sea slugs (Gastropoda: Opisthobranchia) are characterized by extensive morphological homoplasy. In particular, reduced or absent shells are predominant throughout the group. This trend towards shell loss has resulted in a poor fossil record. DNA-based phylogenies have been helpful in improving our understanding of the evolution of this group and major clades are emerging. We report 13 new complete opisthobranch mitochondrial genomes that provide robust support for some of these emerging nodes. We name three new clades within the Opisthobranchia, the Actopleura (Acteonoidea plus Nudipleura), Placoesophaga (Cephalaspidea plus Anaspidea), and Siphoglossa (Sacoglossa plus the Siphonaria). Finally we use molecular clock dating that suggests an earlier opisthobranch divergence than previously reported. The implications of this evolutionary scenario are discussed.     

Contrasting predation pressure of different ground beetles on slugs and their eggs

Slugs such as Deroceras reticulatum Müller (Pulmonata: Agriolimacidae) cause crop losses in temperate regions worldwide. Numerous species of ground beetles (Coleoptera: Carabidae) feed on slugs, but possible interactive effects are poorly known. Here, we compared predation pressure on slug eggs and slug immatures among Abax parallelepipedus Piller and Mitterpacher, Pterostichus niger Schaller, and Pterostichus melanarius Illiger. The latter was most effective against slug eggs but least effective against immature slugs compared to the other species, demonstrating some specificity of ground beetle predation on life stages. Slug egg predation of P. niger in combination with both other species was synergistic, with up to twice as many eggs consumed as for single species treatments. The effect of species combinations on immature slugs showed no differences from expectations based on single species treatments. Our results indicate that combinations of ground beetle species are favourable for the suppression of slugs in early life stages.     

Ultrastructure of the daughter sporocyst and developing cercaria of Schistosoma japonicum in experimentally infected snails, Oncomelania hupensis hupensis

Ultrastructure of daughter sporocysts and cercariae of Schistosoma japonicum were studied 2 and 4 months after infection of Oncomelania hupensis hupensis. The body walls of daughter sporocysts are similar at all infectious stages. They consist of an external syncytial tegument on a basement membrane, and an internal cellular subtegument surrounding a body cavity containing developing cercariae. The cercariae embryos develop 2 months after infection from germinal balls in the brood chamber of the daughter sporocyst. They are at first enveloped by a primitive epithelium rising from the daughter sporocyst. Four months after infection, the cercariae were almost fully developed and the primitive epithelium had degenerated. The body wall of the cercaria consists of a thin tegument covered by a surface coat of fibrous material and connected to the subtegumental cells by cytoplasmic processes. The matrix of the tegument contains numerous dense bodies, vacuoles, and spines. Two types of sensory structures - uniciliated and multiciliated - are found at the anterior tip of the cercaria. There are five pairs of penetration gland cells of two distinct types differentiated by the morphology of secretory granules. Flame cells are found in both daughter sporocysts and in cercariae. The cilia of the flame cells are characterized by the typical 9 and 2 cilium pattern.     

The role of bithyniid snails (Gastropoda: Bithyniidae) as hosts of trematodes of the family notocotylidae in ecosystems of different climatic zones of the West Siberian Plain

The results of long-term investigations (1994–2012) of an infection rate of trematodes of the family Notocotylidae Lühe, 1909 in the first intermediate hosts (Bithyniidae family) are discussed. The bithyniid snails (11348 Bithynia troscheli (Paasch, 1842) and 4347 Bithynia tentaculata (Linne, 1758) in 1994–2012 from Western Siberia have been studied. Parthenitae and cercariae of the family Notocotylidae belong to three species: Notocotylus imbricatus Looss, 1894, Szidat; N. parviovatus Yamaguti, 1934 [syn.: N. chionis Baylis, 1928] and Catatropis verrucosa (Frohl.) Odhner, 1905. The extensiveness of infection of bithyniid snails by the tre-matodes (parthenitae and cercariae) of the family Notocotylidae in rivers basin Ob, Irtich, Karacyk and Chany Lake is analysed. The level of the infection of bithyniid snails by trematodes (parthenitae and cercariae) does not exceed one percent in different reservoirs. The similar data have been obtained during long-term studies in the estuare of the Kargat river, and in the Ob river (near Novosibirsk). The percentage of infected B. tentaculata was significantly higher than of infected B. troscheli in the total (1.79 and 0.32% accordingly, χ² = 95.1, p < 0.001), and in different reservoirs, too. The infected bithyniid snails are recorded in waterbodies of all four basins only in steppe (0.52 ± 0.37%) and forest-steppe zones (0.76 ± 0.07%). Bithyniid snails from waterbodies of the forest zone of the West Siberian Plain were not infected with parthenitae and cercariae of the family Notocotylidae.