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PubMed1976

Exchanges of sodium and chloride at low salinities by Nereis diversicolor (Annelida, Polychaeta).

1. Experiments to compare the exchange (total influx) of sodium and chloride in the polychaete Nereis diversicolor in steady-state adaptation to very low salinities are reported. 2. The Na-uptake mechanism shows a high affinity for sodium, reaching half the maximal uptake rate at an external Na-concentration of 8-10 mM/liter (ca. 2% SW), and becomes "saturated" or reaches a plateau of uptake at concentrations of 40-50 mM/liter (ca. 10% SW) up to ca. 350 mM/liter (75% SW), above which Na-exchange is proportional to the external concentration. 3. The Cl-uptake curve differs from the Na-uptake curve in showing a relative depression at very low salinities before reaching "saturation" at Cl-concentrations of 50-60 mM/liter (ca. 10% SW). Cl-uptake becomes proportional to external concentration in salinities of 50% SW or greater, suggestive of passive diffusion in the ionic and osmotic conforming range. 4. It is shown that the permeability of the body wall, both to Na and to Cl, is reduced at very low salinities, thus destroying one of the assumptions upon which a previously-presented balance-sheet for chloride exchanges in N. diversicolor was based (Smith, 1970a). 5. Attempts to demonstrate an activation of the Na-uptake mechanism at very low salinities were inconclusive; reduction of body-wall permeability to sodium masks any possible activation. 6. It is suggested that the inside-negative body-wall potential is related to the depression of the Cl-uptake curve in salinities below 10% SW.

Animals↗
PubMed1979

[Determination of apparent mean mass of proteins associated with heme in the hemoglobin molecule of Arenicola marina (L.), Annelida, Polychaeta].

Protein and iron concentrations and maximum combined oxygen concentration were measured in the blood of the lugworm Arenicola marina. The calculated mean molecular mass of the heme-associated proteins was higher than that reported for known invertebrate and vertebrate intracellular hemoglobins. The difference is probably due to the presence of polypeptide chains not linked to heme groups in the extracellular annelid hemoglobins.

Animals↗
PubMed1975

[Caudal regeneration in the presence of a supplemental nerve cord grafted dorsally in Nereis pelagica L. (Annelida Polychaeta)].

In Nereis pelagica, the existence of an additional nerve cord grafted dorsally induces the differentiation on the dorsal face of the regenerate of a supernumerary area with ventral characteristics, provided the grafted nerve cord regenerates posteriorly. These results led us to think that the dorse-ventral differentiation of the body wall doesn't depend upon the nature of the stump region but is controlled by the nerve cord regenerating in the area.

Animals↗
PubMed1976

[Elemental chemical composition of Scolelepis fuliginosa (Annelida, Polychaeta): effect of growth conditions].

The elemental chemical composition of Scolelepis fuliginosa was comparatively with specimens reared in laboratory and from a natural population. The carbon-nitrogen ratio variations show a certain homogeneity of composition in juveniles and young sexed and a sexual dimorphism in adults. C/N ratio of the laboratory specimens is not significantly different from that of the ones from natural surroundings. But, when these are kept several weeks in captivity, this ratio considerably decreases.

Age Factors↗
PubMed1976

[Demonstration of the dorsal character of the body wall of the aneurogenic regenerate of Nereis pelagica L. (Annelida, Polychaeta)].

In Nereis pelagica, graft of dorsal or ventral parts of a regenerate edified in the absence of nerve cord (=aneurogenic) on the ventral or dorsal face of a normal host demonstrates a completely dorsal nature of the body wall in these special regenerates. The results indicate that the nerve cord is involved in setting up regenerate dorso-ventral polarity by fixing differentiation of the ventral characters in the area located near by; without it , only the dorsal character is expressed.

Animals↗
PubMed1976

[Stability of determination and differentiation of the somatic sexual characters in Nereis pelagica L. (Annelida polychaeta)].

Experiments of regeneration in situ or on grafts were carried out to test the stability of determination of the somatic sexual characters in Nereis pelagica. The sexual characters of the parapodial cirri (male and female swellings, male crenellations) are always expressed on stump or regenerate according to the genetic sex. Supernumary parapodia which developed at the site of junction of the heterologous faces of host and graft of opposite sexes, might have the characters of either sex; this result can be interpreted by supposing that a supernumary parapodium is derived from tissues of either host or graft, of the corresponding sex. Conversely, the pygidial papillae, which normally occur only on the heteronereid male, will appear on regenerating female pygidia, triggered to transform to the heteronereid condition naturally or by decerebration, with a frequency depending on the age of the regenerate, the length of the regenerate, and the genital condition of both the stump and the regenerate. It is concluded that the presence of the papillae is not a sex-specific character, but that their development is normally inhibited in the maturing female.

Animals↗
PubMed2026

Diverse methyl-end desaturases enable LC-PUFA biosynthesis across Annelida.

Recent studies have demonstrated that annelids possess front-end desaturases and elongases involved in the biosynthesis of physiologically important long-chain polyunsaturated fatty acids (LC-PUFA). However, methyl-end desaturases (ωx desaturases), enzymes that play a central role in the de novo biosynthesis of polyunsaturated fatty acids and their subsequent conversion into LC-PUFA, have so far been reported in only a limited number of polychaete species. To advance our understanding of ωx desaturases across the phylum Annelida, this study performed a comprehensive molecular and functional characterisation of these enzymes in the major annelid taxa Polychaeta, Clitellata and Sipuncula, encompassing species from diverse taxonomic groups and ecological niches. A total of 110 ωx desaturase sequences were retrieved from available genomes and transcriptomes. The number of ωx desaturase genes varied among species, ranging from zero to four copies. Phylogenetic analyses revealed that annelid ωx desaturases are classified into two major clades, designated Cluster A and Cluster B. Analyses of histidine-box motifs and exon-intron organisation revealed conserved patterns within each clade. Functional characterisation of ωx desaturases from Eisenia fetida (Clitellata) and Sipunculus nudus (Sipuncula), together with previously published data from polychaetes, demonstrated that annelids generally possess two ωx desaturases, one with Δ12 desaturase activity and another with ω3 desaturase activity. Collectively, these results demonstrate that annelids possess a phylogenetically and functionally diverse ωx desaturase repertoire that underpins their LC-PUFA biosynthetic capacity and may reflect adaptation to different ecological and nutritional environments.

Animals↗
PubMed1976

Isolation, characterization and oxygen equilibrium of an extracellular haemoglobin from Eunice aphroditois (Passas).

The extracellular haemoglobin from the polychaeta,Eunice aphroditois, existed as a mixture of a heavy major component (so20, w = 56.96 +/- 0.125) and a light minor component (so20, w = 10.00 +/- 0.13S), the latter probably being a dissociation product of the former. The molecular weight of the purified heavier component, as detetermined by sedimentation equilibrium, was 3.44 x 10(6) +/- 0.04x10(6). The molecule had the electron-microscopic appearance typical of annelid haemoglobins, consisting of a stack of two hexagonal plates, with dimensions 26.32 +/- 0.27 nm across the flats of the hexagon, height of stack 17.86 +/- 0.34 nm. The sugar composition is reported, and the isoelectric point was approx. pH7.8. The haem content was 2.31 +/- 0.01%, corresponding to a minimal mol.wt. of 26700. Detergent/gel electrophoresis revealed the presence of at least four bands with molecular weights in the range 14600-31000. Five N-terminal amino acids were found. In addition to the 10S component, which co-existed with the 57S component at all pH values in the range 4.0-10.6, at low pH values (less than pH.5.0) A 16S and a 1.9 S component were found. The absorption and circular-dichroic spectra are reported, and the alpha-helical content, calculated from the ellipticity at 222 nm, was about 40%. The molecule bound O2 co-operatively with a maximum value of the Hill coefficient, h, of 3.9. Over the pH range 7.0-8.0 there was a positive Bohr effect.

Amino Acids↗
PubMed1976

Observations on the feeding mechanism, diet and digestive physiology of Histriobdella homari Van Beneden 1858: an aberrant polychaete symbiotic with North American and European lobsters.

1. The aberrant annelid Histriobdella homari (Polychaeta:Eunicida) lives in the branchial chambers of the marine lobsters Homarus americanus and H. vulgaris where it feeds on the rich microflora of bacteria, blue-green algae and related organisms which grow on the inner surface of the branchial chamber, the setae fringing the edges of the carapace, the gill filaments and, especially, the surfaces and setae of the epipodite plates between the gills. H. homari, therefore, is to be regarded as an epizoic microphagous cleaning symbiote of the lobsters. 2. The alimentary canal consists of mouth, buccal cavity, oesophagus, proventriculus, stomach, intestine and anus. The much-modified proboscis lies ventrally below the oesophagus and proventriculus, with its anterior portions protruding into the rear of the buccal cavity. 3. The proboscis consists of two fixed parallel mandibles, a transverse carrier which slides upon the mandibles and to which is attached, posteriorly, a median flexible dorsal rod and, anteriorly, four pairs of movable articulated maxillae, paired external and internal retractor muscles and various tensor, flexor and extensor muscles. 4. Contraction of the retractor muscles withdraws the carrier and maxillae posteriorly, causing bowing of the dorsal rod which is fixed at its posterior end. Relaxation of the muscles allows the rod to straighten and, thus, causes protraction of the carrier and protraction and lateral expansion of the maxillae. Contraction and relaxation of the relaxation of the retractor muscles are supplemented by appropriate changes in the other muscular components of the proboscis. 5. During feeding the serrated anterior ends of the mandibles are applied to the food, the maxillae are fully expanded and then dawn ventro-posteriorly toward the mid-line by contraction of the retractor muscles in the effective movement of the feeding mechanism. This draws the food organisms across the anterior ends of the mandibles, detaching them from the substratum and allowing their ingestion by ciliary action. The first pair of maxillae are also capable of independent action and can be used while the remainder of the proboscis apparatus is held in the protracted position. 6. Detached microorganisms are entangled in a sticky mucous secretion from the salivary glands; other salivary secretions provide a transport medium for the clumped particles and a third set contain C-esterases which initiate digestion. 7. Ingested food is held briefly in the proventriculus, then passed to the stomach where gland cells secrete A- and C-esterases which continue and extend the digestion initiated by the salivary C-esterases. 8. Some soluble products of gastric digestion are taken up by absorptive cells in the stomach wall and their digestion is completed intracellularly by enzymes which include beta-glucuronidase. Others pass into the intestine for absorption and completion of digestion by cells similar to the gastric absorptive cells but which lack beta-glucuronidase...

Animals↗
PubMed1978

Possible involvement of putrescine in nucleolar formation in early embryos.

Continuous treatment of developing eggs of the polychete Ophryotrocha labronica with alpha-methylornithine, which inhibits synthesis of putrescine, led to arrest of development at gastrulation. The present ultrastructural analysis suggests that the arrest of development is due to failure to form nuclei, and thus reveals a possible role for putrescine in nucleolar formation. Further support for this contention was provided by means of electron-microscopical autoradiography. It was found that newly synthesized putrescine, derived from administered 3H-ornithine, labeled the nucleoli intensely at the time of their normal appearance during gastrulation, the time at which the rate of endogenous putrescine synthesis is maximal. These observations have led to the conclusion that putrescine synthesis may be directly involved in formation of nucleoli.

Animals↗
PubMed1976

The fine structure of polychaete septate junctions.

Epidermal septate junctions of Nereis sp. and Cirriformia sp. fixed with OsO4 or glutaraldehyde/OsO4 display variable structure in electron micrographs. In transverse section the septa are often indistinct and obscured by opaque material that fills the junctional cleft. Septa (spaced at 180--280 A) are more clearly defined in slightly oblique transverse section; they exhibit an electron lucent center and appear to be linked by arms. En face views of the junction show a honeycomb pattern. Cytoplasmic faces of junctional membranes are backed with plaques opposite the septa. Lanthanum used as a tracer delineates junctional structure in negative contrast. In transverse section a chain-like lattice is present in the junctional cleft. En face vies show parallel rows of pleated elements often linked by arms into honeycomb arrays. Oblique sections demonstrate that these pleated elements are continuous with the chain-like lattice seen in transverse sections. Lanthanum does not pass entirely through the junction. Lanthanum reveals that the septa have a very intricate substructure, but it is difficult to visualize the architecture that could generate the various images presented by these junctions when seen in different orientations. However, it is clear that these junctions possess some features that are diagnostic of several supposedly different types of septate junctions in invertebrates.

Animals↗