Two sperm types in the spermatozeugmata of Tubifex tubifex (annelida,oligochaeta)

The spermatozeugmata (sperm bundles lacking a distinct wall) from the spermathecae of Tubifex tubifex are composed of two different zones: an internal axial cylinder containing conventional spermatozoa and an external cortex composed of modified spermatozoa, tightly packed together. The conventional spermatozoa conform to the classical clitellate scheme: very long and thin with a complex acrosome, a filiform nucleus, small mitochondria, and a flagellum with Y links and β glycogen granules as accessory structures. The modified spermatozoa show “empty” acrosomes, degenerating nuclei, and tails which contain γ glycogen granules. The tails are helically wound around the spermatozeugma and are connected to each other by junctional complexes. The tips of the cortical tails are free and move with a metachronal wave. The presence of two sperm types in tubificids is discussed and a protective function for the modified cortical spermatozoa is proposed.     

The ultrastructure and histochemistry of the spermathecae of Tubifex tubifex (Annelida: Oligochaeta)

The wall of the spermathecal ampulla in Tubifex tubifex consists of epithelial, muscular and peritoneal layers. The epithelial surface contains closely microvilli while lateral and basal plasma membranes are extensively convoluted. Epithelial cytoplasm exhibits a vertical zonation of subcellular components. The distal zone contains filiform secretory particles which are orientated perpendicular to the apical surface; extrusion occurs by their fusion with the plasma membrane between the bases of neighbouring microvilli. Mitochondiral and Golgi zones, the latter containing the nucleus, subtend the distal zone. The basal zone, composed of vertical compartments formed by the folded plasma membrane, is rich in α-glycogen rosettes. The distal epithelium and lumen material contain neutral mucopolysaccharides and carboxylated acid mucopolysaccharides in conjunction with neutral protein. The ultrastructure of the spermathecal duct wall is comparable with that of the ampulla but is characterized by extremely long microvilli and a prominent musculature.     

The influence of anaerobiosis on the levels of adenosine nucleotides and some glycolytic metabolites in tubifex sp. (annelida,oligochaeta)

• 1.1. In Tubifex sp. the amounts of ATP, ADP and AMP, and of glucose, glucose-1-P, glucose-1-P, glucose-6-P, fructose-6-P and fructose-1, 6-P were measured after experimental anaerobiosis.
• 2.2. The energy charge decreased from 0.84 to 0.07/0.69 within 6–9 hr of anaerobiosis.
• 3.3. During long term anaerobiosis there was no change from 0.70/0.69.
• 4.4. The concentrations of glucose, glucose-6-P and fructose-1,6-P increased somewhat during an initial phase of anaerobiosis.
• 5.5. The data are discussed with respect to the regulation of energy metabolism, especially during the transition of aerobic to anaerobic metabolism.
• 6.6. It is concluded that this transition is accomplished within 6–12 hours.

     

The leukocytic organ of the megascolecid earthworm,Amynthas diffringens (annelida,oligochaeta)

Leukocytic organs of Amynthas diffringens are aggregations of leukocytes contained within a smooth muscle and stromal cell framework suspended in the coelom. Elongate processes of stromal cells subdivide each organ into numerous cell-filled compartments and are perforated by 130-nm pores that may permit the exchange of humoral substances between compartments, or between the organ and the surrounding coelomic fluid. We divide leukocytes within the organs into four morphotypes. Phagocytic leukocytes have many lysosomelike vesicles and may possess phagosomes. Mature types I, II, and III granulocytic leukocytes share certain features but are readily distinguished by cell shape and by the size, shape, and electron density of the cytoplasmic inclusions. Immature as well as mature phagocytes and granulocytes occur within these organs, suggesting that they are sites of leukocyte maturation and storage. Concentrations of leukocytes within the organs result in extensive cell to cell contact, especially within islets and tightly packed cords. Phagocytosis of cell debris occurs throughout the organs. Immature stages of the four morphotypes are difficult to distinguish even at high magnification, raising the possibility that they may originate from a common precursor. Our inability to observe mitoses or to detect lymphocytelike stem cells suggests that immature leukocytes migrate to the organs via coelomic fluid from as yet unidentified primary sites of production.     

Cohort cultures of Tubifex tubifex forms

By means of cohort cultures at different temperatures, the life cycles of two sympatric forms of T. tubifex have been compared: the normal T. tubifex tubifex and the blanchardi forms. Although the two forms have certain basic similarities, the blanchardi form tolerated low temperatures less well, requiring a longer time to develop to maturity and producing fewer ova. The threshold temperature for development appeared to be around 8 °C, notably higher than for the normal form around 0 °C. Moreover, for the blanchardi form, resistance was lower and mortality higher for embryos and throughout the life cycle. Cross-breeding tests were carried out, along with cultures of individuals serving as controls for partheno-genetic activity. In cross-breeding, pairs produced progeny similar to the normal form only, most likely derived not from eggs fertilized by the partner, but from parthenogenetic eggs. As a matter of fact, only the normal form was able to reproduce through parthenogenesis. Thus, the two forms have remarkable differences, indicating genetic differences, and they may be considered not as forms, but rather as distinct species.     

The histochemistry and ultrastructure of the clitellum of the enchytraeid Lumbricittus rivalis (Oligochaeta: Annelida)

The monostratified clitellar epidermis of Lumbricillus rivalis consists of supporting cells, granular secretory cells, and globular secretory cells, together with the acid mucous cells typical of normal skin in the anterior and posterior transition zones. The secretion of the granular cells is a neutral glycoprotein with low levels of bound lipid, and that of the globular cells is a sulphated acid mucopolysaccharide lacking detectable protein or lipid.
Ultrastructurally the granular cells possess 1 μm, membrane-bound granules of variable electron density suggestive of maturation changes. The formative granules arise from Golgi vesicles and are moderately electron translucent. They contain parallel-aligned, tubule-like inclusions of 14 nm diameter, observed also in the mature regions of the Golgi. Granules in the mid or apical part of the cell show increased electron density, the formative pattern being wholly or partially obscured and the subunit alignment, when discernable, no longer uniform. Moiré fringe patterns are evident in some granules. The patterns and electron density are lost after pronase digestion. The globular cells contain electron translucent, membrane-bound globules of 2–3 μm diameter with finely fibrous contents. They arise from mature Golgi vesicles and are unaffected by pronase treatment.
The results suggest that the granular cells secrete the cocoon wall and the globular cells the material that surrounds the developing embryos, and are compared with published accounts of other microdrile clitella and with those of the clitellum of lumbricid earthworms.     

The Tubifex tubifex assay for the determination of acute toxicity

An express (3-minute) test for acute toxicity determination by using the oligochaete annelid, Tubifex tubifex, is described. The EC50(Tubifex tubifex) [EC50(Tt)] for movement inhibition was calculated by using a concentration-response dependence. The reproducibility of the test was checked over several years and by several workers. Its applicability is limited to compounds which are soluble in water. The calculated EC50(Tt) indices correlate with LC50 values determined by using the fish, Pimephales promelas (96-hour assay), and with ICG50 values determined by using the ciliate, Tetrahymena pyriformis (48-hour assay) with high statistical significance (r = 0.822, n = 35, and r = 0.927, n = 80, respectively). The correlation between the EC50(Tt) indices and rat oral LD50 values (48-hour assay) was r = 0.519 (n = 67). The correlation within organic compounds was closer (r = 0.635, n = 60) than with the heterogeneous series of chemicals. A similar trend was noticed for the correlation with mouse oral LD50 values (r = 0.479, n = 56) with the heterogeneous series of chemicals, as compared that with the series without inorganic salts (r = 0.605, n = 42), and similarly with mouse intraperitoneal LD50 values, where r = 0.543 (n = 50) with the heterogeneous series of chemicals and r = 0.893 (n = 33) with the series of organic chemicals.     

Ultrastructural aspects of mechano- and chemoreceptors in Branchiobdella pentodonta (annelida,oligochaeta)

The surface receptors in Branchiobdella pentodonta consist of “sense buttons” prevalent on the prostomium, isolated sense cells all along the body of the animal, and free nerve endings. The “sense buttons” are uni- and multiciliated neurosensitive elements and supporting cells together with mucus glandular processes and muscle fibers. In the neurosensitive elements the cilia are always surrounded by cytoplasmic extroversion. The cytoplasm of the apical zone has abundant small dense granules, mitochondria, bands of tonofilaments, and microtubules. The cilium of uniciliated elements originates from three short roots. The highly vacuolated support cells surround the neurosensitive elements, separating them from each other. The “sense buttons” appear to be mechanoreceptors and chemoreceptors, and the isolated sense cells tactile mechanoreceptors, as are the free nerve endings. The surface receptors are compared with those of other Oligochaeta and Hirudinea.     

Interactions among two strains of Tubifex tubifex (Oligochaeta: Tubificidae) and Myxobolus cerebralis (Myxozoa)

Host-parasite interactions influence host population growth, host evolution and parasite success. We examined the interactions among Myxobolus cerebralis, the parasite that causes salmonid whirling disease, and resistant and susceptible strains of the oligochaete host Tubifex tubifex. Strains of T. tubifex with diverse genotypes often coexist in nature and have variable susceptibilities to M. cerebralis infection. Further, parasite proliferation differs by several orders of magnitude among T. tubifex strains. We examined total biomass produced by individual T. tubifex, including progeny production and adult growth, parasite proliferation and prevalence of infection using 2 strains of T. tubifex at 2 myxospore doses in a response-surface experimental design. Total biomass production per individual oligochaete and progeny biomass produced by an individual adult oligochaete were density-dependent for both resistant and susceptible individuals and the effects did not change with the addition of myxospores. However, both resistant and susceptible adults had highest growth when exposed to M. cerebralis. The presence of resistant oligochaetes in mixed cultures did not reduce the infection prevalence or parasite proliferation in susceptible individuals. In natural aquatic communities, resistant strains of T. tubifex may not reduce the effects of M. cerebralis on the salmonid host, particularly if sufficient numbers of susceptible T. tubifex are present.     

Caudal regeneration in Tubifex tubifex (Oligochaeta, Tubificidae) following copper exposure

Abstract. The oligochaete, Tubifex tubifex (Oligochaeta, Tubificidae), is capable of the auto-tomization and regeneration of missing body parts. The posterior end of the worm is subject to autotomy (e.g., after predation or after exposure to toxic substances) and can be regenerated thereafter. Despite the ecological importance of T. tubifex , processes of autotomy and regeneration have been little studied. This work describes daily morphological and histological observations of caudal regeneration of this worm. We also compared regeneration processes when autotomy was induced by artificial transsection of the worms (control worms) and by exposure to copper ion, a frequently encountered environmental contaminant. The worms regenerated a functional posterior end (defecation possible) in 7 d as well as a prepygidial zone from which new segments could be regenerated. In T. tubifex , regeneration involved the presence of activated mesoblastocytes in the worm, increased number of neoblasts, and the increased migration of these cells. However, Cu²⁺ did not affect these processes, since no difference could be detected between regeneration of control and Cu-autotomized worms.     

Subunits of the extracellular hemoglobin of Tubifex tubifex.

The molecular weight of the extracellular hemoglobin of Tubifex tubifex determined by equilibrium sedimentation is 3.0 +/- 0.2 . 10(6). Polyacrylamide gel electrophoresis in sodium dodecyl sulfate showed that the hemoglobin dissociated into four subunits: 13 000 (subunit 1), 21 000 (subunit 2), 23 000 (subunit 3) and 47 000 (subunit 4); in the presence of mercaptoethanol two subunits were observed, 13 000 +/- 1000 (subunit I) accounting for 70--80% of the whole molecule, and 26 000 (subunit II). Electrophoresis of the subunits obtained in the absence of mercaptoethanol showed that subunit I originated from subunits 1 and 4, while subunit II originated from subunits 2 and 3. These relationships were supported by N-terminal group determinations. Gel filtration in 6 M guanidine hydrochloride showed that the molecular weight of subunit I is 17 500 and that of subunit II, 36 000. Tubifex hemoglobin appears to consist of at least seven polypeptide chains.     

Selective feeding by the aquatic oligochaete Tubifex tubifex (Tubificidae,Clitellata)

The particle size distribution of faecal pellets produced by the tubificid worm Tubifex tubifex in laboratory culture, was measured with a Coulter® Multisizer. The faecal material from worms cultured in a range of sediments was composed of particles with a mean diameter of less than 63 m, and only a few isolated larger particles were found by microscopic analysis. This suggests that this species actively selects the silt-clay fraction, avoiding larger sand particles. A more detailed analysis of faeces revealed that about 75%, by volume, was composed of particles with a mean diameter < 25m, and the mode was < 10m. T. tubifex fed selectively on the organic rich particles of the sediment, and this feeding was independent of particle size. Measurement of the organic content of faeces (measured as % loss on ignition) showed that they had a consistently higher organic content than the sediment, considered as whole sediments or the <63 m sieved fraction. On the basis of these results, we hypothesise that this species exhibits two levels of selectivity in its feeding behaviour. Thus selection is primarily based on particle size, avoiding the ingestion of sand particles and also, on the preferential selection of particles associated with organic material, within the fine (silt-clay) fraction of the sediment.     

Nuclear fragmentation characterises paraspermiogenesis in Tubifex tubifex (Annelida, Oligochaeta)

It is known that tubificine oligochaetes produce two types of spermatozoa: eusperm, fertilizing sperm with regular haploid DNA content; and parasperm, with a much lower DNA content, protecting and carrying the eusperm. Whereas mature spermatozoa and spermatids of the two lines are easily recognized by their morphology and DNA content, little is known about the first steps of differentiation of the two lines. This subject is addressed here in two ways: we have measured DNA content by a new method based on confocal laser microscopy and found that the total DNA content of parasperm cysts is extremely variable and equal or lower than total DNA content of eusperm cysts. Then we focused on the spermatocytes, and we found that the cells which will form paraspermatids undergo a peculiar kind of nuclear fragmentation which differ greatly from a regular cell division. During fragmentation DNA is distributed unevenly among the spermatids and this gives rise to a great and variable number of parasperm with variable DNA content. Immunocytochemical assays revealed that a proper meiotic spindle is never formed during fragmentation and that actin may play an important role in the chromatin division. Electron micrographs showed that the centrioles undergo a phenomenon of mass reproduction similar to that found in ciliated epithelia which supplies each of the numerous paraspermatids of its basal body. Mol. Reprod. Dev. 59: 442-450, 2001.     

The effect of cohabitation of Tubifex tubifex (Oligochaeta: Tubificidae) populations on infections to Myxobolus cerebralis (Myxozoa: Myxobolidae)

The competitive interactions between susceptible and resistant Tubifex tubifex (Oligochaeta: Tubificidae) exposed to Myxobolus cerebralis (Myxozoa: Myxobolidae) infections were investigated in two laboratory trials. Competition was assessed by the total parasite production over the course of the trials in mixed and pure cultures of M. cerebralis exposed worms, and by the genetic analyses of worms from the control and experimental groups at the beginning and end of the experiments. Mixed cultures of resistant and susceptible worms showed a 70% reduction in production of parasites released when compared with pure cultures of susceptible worms. In studies with laboratory and field-collected oligochaetes the mixed cultures at the end of the cohabitation experiments were dominated by resistant Tubifex from lineage V (HB strain) this strain of Tubifex has a competitive advantage over worms from other lineages. The results of this study suggest that certain species of Tubifex may be dead-end hosts to M. cerebralis by absorbing or inactivating the parasite and may also show greater survival compared to susceptible oligochaetes in certain whirling disease enzootic habitats.     

Population analysis in mass cultures of Tubifex tubifex

Mass cultures of Tubifex tubifex from Lake Orta were kept in the lab at 20 °C starting with different initial densities (10, 45, 86, 161 ind · jar^–1), with the aim of evaluating the effect of density on population numbers and on population parameters. The results show that density mainly controls fecundity, growth, maturation and ovigeration rates. Growth rates and mean number of eggs laid/ovigerous (R₀) are inversely related to density, but generation time appears to be directly related. Very low or very high initial densities display, at different times of the culture history, efficient density controls. Intermediate N₀ seem to bring about situations of bad control, easily leading to numerical overshoots. A possible implementation of a population dynamics model (Bonomi & Di Cola, 1980), originally used for laboratory observations on T. tubifex cohorts was considered, including some density control functions derived from our observations on cohort and mass cultures in some transfer rates and in fecundity rate.     

Investigations of the blood capillary system of Tubifex tubifex

The blood capillary system of Tubifex tubifex has been investigated using various methods of killing and fixation. When the worm was killed slowly and in a relaxed state capillary systems to both the intestine and the body wall showed clearly and have been described.