Unusual model of lumbriculids' helical muscles: comparison with body wall muscles in other microdriles

Longitudinal body wall muscles of lumbriculids are characterized by unique peculiarities; they are ribbonshaped, with regularly distributed Z-elements and sarcotubules crossing the fibres from one side to another. These act as a sequence of pivots for mechanical and functional control during contraction. Myosin filaments are equally ribbon-shaped, and in the XZ plane they appear sigmoid. All these characteristics can be deduced from a comparison between theoretical computerized images and corresponding electron micrographs. The muscles of lumbriculids are only apparently similar to those of enchytraeids and tubificids, and are completely different from the muscles of haplotaxids and branchiobdellids. A comparison between body wall muscles of these microdriles suggests the opportunity of using the muscle organization and ultrastructure as a taxonomic character.     

Peripheral vascular apparatus in some aquatic oligochaetes with special references to haplotaxids

The organization of the peripheral vascular apparatus in two haplotaxids has been studied and compared with that of other microdriles. Considerable differences in the circulatory systems of Pelodrilus leruthi and Haplotaxis gordioides, especially in relationships to the body wall muscle fibers, separate and distinguish the two animals. Different organizations of the peripheral apparatus that can be observed in these microdriles are: in the first species, capillary vessels have no contact with the body wall; in the second species, capillaries extend between the longitudinal muscle fibers until they reach the body surface, thus approaching the situation in megadriles where circulation can become intraepithelial.Generally, vessels hanging in the coelom are of a large diameter. When a capillary network related to the body wall muscle develops, vessels are small in diameter and their walls have variable numbers of contractile elements, ensuring the forced circulation of the blood.     

Utility and relevance of aquatic oligochaetes in Ecological Risk Assessment

Ecological risk assessment (EcoRA) provides both a process and a framework to evaluate the potential for adverse ecological effects occurring as a result of exposure to contaminants or other stressors. EcoRA begins with problem formulation/hazard identification, progresses to effects and exposure assessment, and culminates with risk characterization (an estimate of the incidence and severity of any adverse effects likely to occur). Key components of EcoRA include determining: stressors/contaminants of concern; sensitive, exposed biota; and, appropriate tests and organisms for evaluating effects. Aquatic oligochaetes are not generally used directly in EcoRA because of three major perceptions. First, EcoRA personnel are generally not familiar with or comfortable using this group of organisms. Second, there is believed to be a paucity of widely accepted toxicity tests with these organisms. Third, their taxonomy is considered difficult and uncertain. In fact, aquatic oligochaetes potentially have great utility and relevance to EcoRAs because of factors including: their importance in the aquatic food chain (e.g. prey to fauna including fish and waterfowl; as a vector for contaminant movement through the food chain from bacteria); many species are widely distributed and well studied; representatives include fresh, estuarine and marine species; as a group, they range from sensitive to insensitive over a wide range of environmental insults; they have a long history of use in pollution monitoring and assessment; and, relevant toxicity and biaccumulation tests exist. Toxicity testing under defined conditions is appropriate for problem formulation while more realistic testing for effects assessment (e.g. microcosms) is logistically easier with this group of organisms than with others due to their relatively small size. The importance of aquatic oligochaetes for EcoRA, in particular of sediments, is particularly compelling.     

Inter-species variability in the consumption of algae by oligochaetes

The importance of algae in the diet of the oligochaetesArcteonais lomondi, Uncinais uncinata andLimnodrilus claparedeianus was determined from May 1978 to April 1979 in two lakes located in northern Canada. The lakes were small (130–157 ha), shallow, (<15 m) and mesotrophic. During summer, algae accounted for up to 57–75% by volume of ingested matter inA. lomondi andU. uncinata depending on lake whereas in winter the corresponding range was 10–22%. Dominant algae found in the gut included the diatomsSurirella robusta, Diploneis puella, Amphora ovalis, Stephanodiscus astraea, Fragilaria construens andAchnanthes minutissima. Although the same taxa were ingested byL. claparedeianus, algae always represented <5% by volume of the gut contents. This possibly reflects subsurface feeding in an area where algae were rare. The length distribution of ingested diatoms, ranging from 9 to 250 m, was similar regardless of species in both lakes. Hence, there was no partitioning of algal food resources among oligochaetes.     

The role of oligochaetes in the management of waters

To better understand the role of an aquatic oligochaete in the management of water quality, it was determined if oligochaetes were representative of water quality, if indices based on oligochaetes were widely applicable to access water quality, and if oligochaete assemblages were related to environmental factors other than organic pollution. It was found that if only one monitoring sample a year was taken in December, about 73% of the more common species were collected. Seasonality did not seem to affect the taxa collected except for forms in low presence, e.g., Nais. Several indices we used were not applicable to regulated streams. Oligochaete ordination procedures revealed only a partial picture of the environmental conditions of regulated streams.     

Body wall organization in enchytraeids

The muscle organization of the body wall in some species of oligochaetes belonging to the Enchytraeus genus is described. No differences have been detected in their circular muscles, whereas longitudinal muscles show significant differences, allowing an easy identification of the various worm species. In particular, differences are noticeable in the external longitudinal layer. These observations suggest that structural and ultrastructural muscle fiber organizations can be used as a taxonomic tool.     

Species composition,distribution, and abundance of oligochaetes in the Kanawha River,West Virginia

Species composition, distribution, and abundance of oligochaetes in the Kanawha River, West Virginia, were investigated. Eighteen taxa of oligochaetes including 7 tubificids, 8 naidids, and representatives of the families Enchytraeidae, Lumbriculidae, and Aelosomatidae were collected. While most of the species collected are cosmopolitan, Pristina synclites and Stephensoniana sp. previously reported only from Asia and Africa were collected in the Kanawha. Other peculiarities of the Kanawha oligochaete fauna included the common occurrence of specimens of Limnodrilus cervix and Limnodrilus hoffmeisteri with atypical penis sheaths. The dominant and most widely distributed of the Kanawha River oligochaetes were immature tubificids lacking capilliform chaetae, Branchiura sowerbyi, Dero cf. obtusa, Limnodrilus hoffmeisteri, and Aulodrilus pigueti.Oligochaete densities ranged from 401–2403 individuals/m² in areas presumed to be nonpolluted, to 1–671 individual/m² at sites with suspected toxicity. The highest density of oligochaetes (2835 individuals/m²) occurred at a site of organic enrichment.     

Depth distribution of oligochaetes in Lake Baikal (Siberia - Russia)

In the course of a preliminary sampling program, oligochaetes were collected along two transects in soft sediments in Lake Baikal. The number of oligochaetes present in the samples was counted, without distinguishing between species. The results suggest an exponential decrease in number of individuals (N) relative to depth (11,165 N m^–2 at 21 m, 265 N m^–2 at 1200 m). Most oligochaetes were found in the top 7 cm of sediment. The orange colour of the sediments suggests a high oxygen availability, even at the greatest water depths.

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Résumé Au cours d'un programme d'échantillonnage préliminaire, les oligochètes du lac Baïkal ont été récoltés dans le sédiment mou prélevé le long de deux transects. Les oligochètes présents dans les échantillons ont simplement été dénombrés, sans identification déspèces. Les résultats suggèrent une diminution exponentielle du nombre d'individus en fonction de la profondeur du lac (11165 N m^–2 à 21 m, 265 N m^–2 à 1200 m). La plupart des oligochètes ont été trouvés dans les 7 premeirs cm de la couche supérieure du sédiment. La couleur orangée du sédiment suggère une grande disponibilité en oxygène, même aux profondeurs les plus grandes.

     

The skeletal muscles of rotifers and their innervation

The skeletal muscles of rotifers are monocellular or occasionally bicellular. They display great diversity of cytological features correlated to their functional differentiation. The cross-striated fibers of some retractors are fast contracting and relaxing, with A-band lengths of 0.7 µm to 1.6 µm, abundant sarcoplasmic reticulum and dyads. Other retractors and the circular muscles are tonic fibers (A band > 3 µm), stronger (large volume of myoplasm) or with greater endurance (superior volume of mitochondria/ myoplasm). All of these retractor muscles are coupled by gap junctions and are innervated at two symmetrical points; they constitute two motor units implicated in withdrawal behaviour.The muscles inserted on the ciliary roots of the cingulum control swimming. They are multi-innervated and each of them constitute one motor unit. They have characteristics of very fast fibers; the shortest A-band length is 0.5 µm in Asplanchna.All the skeletal muscles of bdelloids are smooth or obliquely striated as are some skeletal muscles of monogononts. These muscles are well suited for maximum shortening and are either phasic or tonic fibers.All rotifer skeletal muscles originate from ectoderm and contain thin and thick myofilaments whose diameters are identical to those of actin and myosin filaments in vertebrate fast muscles or in insect flight muscles. There are no paramyosinic features in the thick myofilaments. The insertion, innervation, coupling by gap junctions and other cytological differentiations of rotifer skeletal muscles are reviewed and their phylogeny discussed.     

Vertical distribution and abundance of benthic invertebrates in profundal sediments of Mondsee,with special reference to oligochaetes

Two profundal sediment sites at the same depth (MO₁ and MO₇) in Lake Mondsee differed considerably in their trophic conditions. Based on organic carbon (weight loss on ignition) and redox values, MO₁ sediments could be classified as eutrophic, MO₇ sediment as oligo- to mesotrophic. Investigations on abundance, diversity and vertical distribution of meio- and macrofauna exhibited distinct differences between the two sampling sites. MO₇ showed a much higher diversity than MO₁. Seven species of ostracods and oligochaetes respectively, were found at MO₇, but only two species of oligocheates at MO₁. The vertical distribution of meiofauna at MO₇ corresponded to redox values. Chironomids were found in the uppermost 4 cm of sediments. Oligochaetes penetrated 15 to 20 cm into the sediment. Nearly 100% of the adult oligochaetes and cocoons occurred only below the first three centimeters of sediment. Their distribution patterns are discussed.     

Comparative body wall musculature and muscle fibre ultrastructure in branchiobdellidans (Annelida: Clitellata), and their phylogenetic significance

The body wall muscles in five species of branchiobdellidans are all arranged in the oligochaete pattern and the muscle fibres are obliquely striated. The structure of the circular muscle fibres do vary to some degree. The longitudinal muscle fibres in Ankyrodrilus legaeus, Branchiobdella kozarovi, and Xironogiton instabilis all are round circomyarian and thus double-obliquely striated. These species represent three of the four genera composing the family Branchiobdellidae. Although Bdellodrilus illuminatus and Cambarincola fallax, from the families Bdellodrilidae and Cambarincolidae, respectively, also possess a few round circomyarian fibres, most are polyplatymyarian comparable to single-obliquely striated fibres. A similar division of branchiobdellidan families is obtained based on the number of anterior nephridial pores. The muscular structure in the branchiobdellidans shows both similarities and differences with the leeches and the lumbriculid oligochaetes. One phylogenetic explanation for this is that the branchiobdellidans separated from the common clitellate ancestor before the oligochaetes and leeches became recognizable taxa.     

Factors influencing the distribution of chironomids and oligochaetes in profundal areas of Spanish reservoirs

A canonical correlation analysis was performed in order to explain the distribution and abundance of the profundal macrozoobenthos in 71 Spanish reservoirs. Two sets of variables were considered: one set consisted of subgroups of benthic organisms based on their feeding strategy, and the other consisted of environmental variables related to the trophic state of the reservoir.The results showed that densities of phytophagous chironomids decreased with water depth and increased with oxygen content in the bottom waters, while Tanypodinae densities increased with rising densities of phytophagous chironomids and/or oligochaetes, revealing their strong dependence on the abundance of available prey. The abundance of oligochaetes and phytophagous chironomids showed a disjunct distribution with season and depth, suggesting the importance of food quality and sediment texture.Oxygen availability and water depth acted as governing factors for the zoobenthos. Chlorophyll-a was of secondary importance and correlated inversely with the abundance of benthic fauna, especially in summer. Autogenic production coupled with inputs of allochthonous coarse particulate organic matter and a long stratification period lead to long lasting anoxia that reduces the benthic fauna in Spanish reservoirs.Only up to 18% of the variability in the biological data could be associated with the environmental factors considered. Thus, factors other than the trophic state are much more important in reservoirs. Fluctuations of the water level and inputs of organic and inorganic materials coming from the basin are greater than in lakes and act as stressing factors for the benthic fauna.     

Top–down control of benthic heterotrophic nanoflagellates by oligochaetes and microcrustaceans in a littoral freshwater habitat

1. We investigated trophic interactions between benthic heterotrophic nanoflagellates (HNF) and oligochaetes and microcrustaceans (cladocerans and copepods) transferred from a silty, littoral freshwater habitat to laboratory microcosms. With a newly adapted experimental design we were able to compute (i) predation rates on benthic HNF by the tested metazoan organisms and (ii) growth rates of the natural benthic HNF population when losses because of this predation were excluded. 2. The experiments covered a temperature range of 4–27 °C and a fivefold variation of predator densities (September 2000–February 2002). For 60% of these experiments, significant predation of oligochaetes and microcrustaceans on benthic HNF was revealed. Predation rates on HNF ranged from 0 to 0.256 day^?1. Growth rates of the benthic HNF assemblage varied from ?0.098 to 0.353 day^?1; they were used to estimate the significance of the measured losses in comparison with possible other loss factors. 3. The data suggested that during the major part of the year a high percentage of the HNF production was consumed in the surficial sediment of the investigated system, resulting in a relatively constant and low HNF standing stock and an uncoupling of benthic bacteria and their protistan grazers. Top–down control by microcrustaceans and oligochaetes was identified as one significant, frequently prevailing regulatory factor, while other parameters responsible for the control of benthic HNF densities remain to be examined.     

An ultrastructural study of the polyp and strobila of Atorella japonica (Cnidaria,Coronatae) with respect to muscles and nerves

Atorella japonica were observed by TEM to examine the nerve plexus in the capitulum of the polyp and the cross-striated muscle cells of the strobila. The nerve plexus included a number of neuromuscular junctions and many interneural synapses. Neuromuscular junctions contained two types of synaptic vesicle: clear and small (ca 75 nm diam.), and dense cored and large (ca 120 nm diam.). The first type of vesicle always appeared near the presynaptic membrane and the second type was distributed behind the former. In interneural synapses, two types of vesicle which were similar to neuromuscular synaptic vesicles were recognized. They were distributed in a pattern similar to that of the neuromuscular synaptic vesicles, but these vesicles were found on both sides of the two synaptic membranes.     

Some aspects of the ecophysiology of Tubificoides benedii and ultrastructural observations on endocuticular bacteria

Tubificoides benedii is regularly found in sulphide-rich sediments with extremely low oxygen tensions and can tolerate anaerobic conditions for several days. Although the anaerobic energy production of marine invertebrates has been well studied, almost nothing is known about the anaerobic metabolism of marine oligochaetes. Preliminary results after measuring end-products during anaerobic incubation show that in contrast to all previously examined marine facultative anaerobe invertebrates T. benedii degrades malate during anaerobiosis. Also, the concentration of free amino acids is extremely low for a marine organism. Low levels of free amino acids could be concomitant with malate utilization: the utilization of the amino acid aspartate (as observed in all other examined marine invertebrates) seems to be excluded by the low concentrations of aspartate and other amino acids in T. benedii.The physiological lab studies were supplemented by ecological investigations in the field and laboratory on the vertical distribution of T. benedii. 90% of the population was always found within the first few cm below the sediment surface. Aquarium observations showed that the posterior end of the worm projects above the sediment surface, where it slowly waves back and forth. This behavior points towards an intestinal respiration. The described orientation, an intestinal respiration and anaerobic energy production could be advantageous in sulphide-rich sediments where O₂ only penetrates a few mm into the sediment. The worm can easily inhabit the first three to four cm by holding its tail in the upper oxygenated sediment and water. Here it would be able to feed on the rich quantities of bacteria at the anoxic-oxic interface and yet still keep up an aerobic metabolism. In addition, its ability to produce energy anaerobically would allow T. benedii to dwell in deeper anoxic sediments for limited periods of time or to survive complete O₂ absence that could develop during low tide.The posterior ends of T. benedii found in a sulphide-rich habitat in the German Wadden Sea were covered with filamentous epibacteria (Dubilier, 1986). Electron microscopy showed that the bacteria were anchored in the cuticle. The association is apparently not pathogenic whereas positive forms of interaction can be envisioned.     

External sense receptors in microdrile oligochaetes (Annelida,Clitellata) as revealed by scanning electron microscopy: Typology and patterns of distribution in the main taxonomic groups

This work summarizes the observations on 30 species of microdriles belonging to the families Naididae (Rhyacodrilinae, Pristininae, Naidinae, Phallodrilinae, and Tubificinae), Phreodrilidae, Lumbriculidae, and Enchytraeidae using scanning electron microscopy. The lumbricid Eiseniella tetraedra, a megadrile species common in typical microdrile habitats, was used for comparison. Microdriles display external ciliate sense structures along the entire body; even at the clitellum and in budding and regeneration zones. According to the shape of the cilia, these sense structures can be divided into receptors of blunt cilia, receptors of sharp cilia, and composed receptors. Sense receptors can be morphologically unconspicuous or clearly defined on sensory buds or papillae. All microdriles studied have receptors of blunt cilia. Enchytraeids have characteristic receptors of short cilia. Pristina (Pristininae), Chaetogaster, Ophidonais, and Stylaria (Naidinae) have receptors of long blunt cilia. Composed receptors were found only in some microdriles and E. tetraedra. Receptors of sharp cilia have been found in most microdriles. Enchytraeids might be the only exception, but sharp cilia are probably present in the amphibiotic Cognettia sphagnetorum. Sensory cells with long sharp cilia might play a rheoreceptor role, and their presence in E. tetraedra and C. sphagnetorum would imply the reappearing of an ancient character that was probably lost with the transit from aquatic to terrestrial habitats. Some lumbriculids have ciliated fields. Anatomically, these structures appear as intermediate between the typical isolate sensory structures of microdriles and the sensillae of the hirudineans. The general pattern in microdriles is that uniciliate receptors and multiciliate receptors are separated, which supports the presumed aquatic origin of the clitellates. J. Morphol., 2010. © 2010 Wiley‐Liss, Inc.     

Pattern of body-wall muscle differentiation during embryonic development of Enchytraeus coronatus (Annelida: Oligochaeta; Enchytraeidae)

The plesiomorphic arrangement of body-wall musculature within the annelids is still under discussion. While polychaete groups show a great variety of patterns in their somatic muscles, the musculature of soil-living oligochaetes was thought to represent the characteristic pattern in annelids. Oligochaete body-wall muscles consist of an outer continuous layer of circular and an inner continuous layer of longitudinal muscles, forming a closed tube. Since designs of adult body musculature are influenced by evolutionary changes, additional patterns found during embryogenesis can give further information about possible plesiomorphic features. In oligochaetes, detailed cell-lineage analyses document the origin of the mesoderm and consequently the muscles, but later processes of muscle formation remain unclear. In the present work, body-wall muscle differentiation was monitored during embryogenesis of thesoil-living oligochaete Enchytraeus coronatus (Annelida) by phalloidin staining. Primary circular muscles form in a discrete anterior-to-posterior segmental pattern, whereas emerging longitudinal muscles are restricted to one ventral and one dorsal pair of primary strands, which continuously elongate towards posterior. These primary muscles establish an initial muscle-template. Secondary circular and longitudinal muscles subsequently differentiate in the previous spaces later in development. The prominent ventral primary longitudinal muscle strands on both sides eventually meet at the ventral midline due to neurulation, which moves the ventral nerve cord into a coelomic position, closing the muscle layers into a complete tube. This early embryonic pattern in E. coronatus resembles the adult body-wall muscle arrangements in several polychaete groups as well as muscle differentiation during embryonic development of the polychaete Capitella sp. I.     

T-system in muscles of microdriles

Ribbon-like longitudinal fibers of the body wall of enchytraeids and lumbriculids are grouped in fuctional units. The organization of subsarcolemmal cisternae, membrane foldings and extracellular spaces between fibers is described. The data seem to indicate that the spaces between fibers within each functional unit are interpretable as T-tubules of a cross-striated fiber.     

Histology and Ultrastructure of the Body Wall in the Phoronid Phoronopsis harmeri

The histology and ultrastructure of the body wall in Phoronopsis harmeriwere studied using light microscopy and TEM. The ectoderm epithelium of tentacles, anterior body region, and ampulla consists of monociliary cells. Gram-negative bacteria were found between microvilli, in the protocuticle of the anterior region, and in the ampulla. The epithelium of the posterior body region lacks both monociliary cells and bacteria. The bundles of nerve fibers run between the layer of epithelial cells and basal membrane. The musculature of the body wall comprises circular and longitudinal muscles. The circular muscle fibers are applied to the basal membrane and constitute a solid layer extending almost throughout the length of the body. This pattern is broken in the posterior body region, where there is no solid layer of circular musculature, and the latter is arranged in isolated muscle bands. In the ampullar (terminal) body region, the inversion of circular and longitudinal muscle layers takes place, so that the latter appears to be pressed against the basal membrane. The apical surfaces of longitudinal muscle cells bear cytoplasmic processes; some of the cells have a flagellum. The basal portion of the longitudinal muscle cells forms a cytoplasmic process containing bundles of tonofilaments. The processes of all cells making up the muscle bands are interwoven and anchored to the basal membrane.     

Comparative study of the cuticle in some aquatic oligochaetes (Annelida: Clitellata)

An examination of the cuticle of six aquatic oligochaete species using transmission electron microscopy revealed a larger morphological variation than previously known. Three freshwater species, Aulodrilus pluriseta, Spirosperma ferox (both Tubificidae), and Pristina breviseta (Naididae), and three marine species, Clitellio arenarius, Heterochaeta costata (both Tubificidae), and Paranais litoralis (Naididae), were investigated. The arrangement of the collagen fibers in the cuticle differs among the studied species. Only S. ferox shows an "orthogonal grid," i.e., layers of parallel fibers perpendicular to each other, as earlier described for lumbricids and enchytraeids. Clitellio arenarius and H. costata have fibers arranged in layers, while A. pluriseta and P. litoralis have irregularly distributed fibers. Pristina breviseta lacks cuticular fibers. The matrix surrounding the collagen fibers (when present) continues outside the fiber layer, making up a thin epicuticle, which has a unique banding in each of the studied species. The external surface of the epicuticle is covered with epicuticular projections. Their number, shape, and attachment to the epicuticle vary among the studied species. Furthermore, a distinctive internal substructure of the projections was observed in H. costata, A. pluriseta, S. ferox, and P. breviseta. Microvilli, extensions from the epidermal cells, penetrate the cuticle and terminate at its outer surface. In three species microvilli were observed to pinch off the epicuticular projections. The size, number, and shape of the latter vary; no typical microvilli were observed in S. ferox.