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At least 19 recordsLinked to original sources
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↗
PubMed2026

De Novo Assembly and Comparative Analysis of the Complete Mitochondrial Genome of Mesenchytraeus (Annelida, Enchytraeidae).

The Changbai Mountain range is one of the key glacial refugia in Northeast Asia. Mesenchytraeus exhibits high species diversity, strong endemism, and widespread cryptic species in this region, for which mitogenomes provide useful molecular markers for exploring cryptic species complexes. This makes Mesenchytraeus an ideal model for studying mitogenome evolution among closely related lineages; however, no mitogenome data have been reported for this genus to date. In this study, we performed de novo assembly, annotation, and comparative analysis of the mitogenomes of 13 Mesenchytraeus species (14 individuals) from Changbai Mountain. All mitogenomes are typical circular molecules containing 37 genes, but putative control regions are rearranged and consistently located between ATP6 and trnR. All species exhibit annelid-specific strand nucleotide biases, characterized by negative GC skew and near-zero AT skew. Codon usage analysis reveals that codon families with wobble U are significantly biased toward mtDNA codons, whereas those with wobble C or G are biased toward non-mtDNA codons, suggesting a conserved mitochondrial codon usage pattern in annelids. All tRNAs form typical cloverleaf secondary structures except trnS2, which lacks the D-stem and the dihydrouridine (DHU) arm in some species. The putative control regions commonly contain complex palindromic repeats, hairpins, and repetitive elements, and may harbor dual replication origins. Phylogenetic analyses support the monophyly of Mesenchytraeus and reveal significant molecular divergence among morphologically cryptic species. This study provides the first mitogenome dataset for Mesenchytraeus and offers new insights into the evolution and replication mechanisms of mitogenomes in Clitellata and broader Annelida.

Mesenchytraeus↗
PubMed1978

Morphological and ultrastructural study of the ventral nerve cord in Branchiobdella pentodonta Whitman (Annelida, Oligochaeta).

The ventral nerve cord of Branchiobdella pentodonta consists of paired ganglia containing three different types of neurons, a central neuropil showing characteristic synapses and of an intersegmental apparatus made up of two large lateral connectives and a smaller ventral one. Some remarkable differences exist between the ventral nerve cord and that found in other oligochaetes; these include the presence of a large dorsal blood vessel, two dorsal muscular cells per metamere, and supportive glial cells ventral to the neuropil which have long transverse processes coming into contact with the segmental nerves.

Animals↗
PubMed1977

Possible sites of ultrafiltration in Tubifex tubifex Müller (annelida, oligochaeta).

The endothelia of Tubifex tubifex Müller consist of myoendothelial cells, chloragocytes, or podocytes. The latter seem to occur only as windows on the ventral vessel which has an endothelium of myoendothelial cells elsewhere. The podocytes are large cells, with several processes on the inner side which ramify into several pedicels. These are aligned upon the outside of the basement membrane which lines the inside of the endothelium. The gaps between adjacent pedicels are about 40 nm wide. In capillaries fenestrated endothelia occur with irregular spacings measuring up to 0.4-1 micron. A diaphragm in podocytes or capillary fenestrations do not seem to exist. The basement membrane is the only continuous layer lining the blood vessels and capillaries of Tubifex with a rather uniform diameter in the range of 50nm. It is the only permeability barrier between blood and coelomic fluid.

Animals↗
PubMed2026

Development and Characterization of Microsatellite Markers for the Euryhaline Polychaete Laeonereis acuta (Annelida: Nereididae) in the Southwestern Brazilian Coast.

Laeonereis acuta is a polychaete species typically found at high abundance in estuarine and coastal lagoon environments. Due to its association with polluted habitats, it is commonly used in ecotoxicological studies. Moreover, its occurrence in spatially discontinuous environments with high environmental variability makes it a suitable model for evolutionary studies of local adaptation, genetic landscape, and early stages of speciation. This study aimed to develop primers and characterize microsatellite markers for L. acuta sampled from three coastal lagoons in southwestern Brazil. A total of 10 loci were characterized based on the genotyping of 40 individuals. The number of alleles per locus ranged from 2 to 19. Evidence of null alleles was detected at five loci, although their frequency decreased when coastal lagoons were analyzed separately. When considering all individuals as a single population, five loci showed positive and significant FIS values, and seven loci deviated from Hardy-Weinberg equilibrium. Maricá and Guarapina exhibited heterozygote excess at several loci, whereas Jaconé showed evidence of population genetic isolation. The 10 microsatellite loci were polymorphic and suitable for population genetic analysis in L. acuta, although these patterns may not necessarily be representative of other geographic regions. These markers may contribute to ecotoxicological studies by clarifying whether physiological responses to pollutants are associated with genetic differentiation among populations. Furthermore, they provide valuable tools for investigating genetic structure and connectivity in discontinuous environments.

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↗
PubMed1979

Unusual granules in the ejaculatory duct of a Microphthalmus species (Polychaeta, Annelida).

The paired prominent ejaculatory ducts of the hermaphroditic polychaete Microphthalmus cf. listensis are surrounded by gland cells the processes of which penetrate the ducts themselves. These cells produce, in separate regions, two different types of spherical granules. Type I is composed of an electron dense and an electron lucent part. Type II granules contain a tubular filament that forms a single or double spiral in the periphery of a more or less unstructured electron dense material. Golgi vesicles give rise to this granule type. During the passage of sperm, these granules are obviously discharged into the lumen of the duct. Here they change form and probably dissolve. Their function is as yet unknown; capacitation of sperm is assumed.

Animals↗
PubMed1979

Autoradiographic detection of indolamine and catecholamine neurons in the nervous system of Owenia fusiformis (Polychaeta, Annelida).

Light- and electron-microscopic autoradiographic studies were carried out on Owenia to detect selectively catecholaminergic and indolaminergic neurons at two appropriate body levels according to the regenerative properties of this annelid, i.e. in the 1st and the 4th abdominal segments. Autoradiographically, intense 3H-5-hydroxytryptamine accumulation is seen in the 1st abdominal segment, and a less intense autoradiographic reaction in the 4th segment. Roughly, a similar difference in the distribution of the label is seen at both levels following 3H-noradrenaline administration. These observations, confirmed by a quantitative uptake analysis, suggest the presence of catecholaminergic and indolaminergic neurons in Owenia.

Animals↗
PubMed1978

Petroleum hydrocarbon resistance in the marine worm Neanthes arenaceodentata (polychaeta: annelida), induced by chronic exposure to No. 2 fuel oil.

1. Three successive generations of the marine polychaetous annelid Neanthes arenaceodentata taken from a laboratory population, were continuously exposed to one of three sublethal concentrations of No. 2 Fuel Oil water-soluble-fraction (WSFs). During each generation larvae, juvenile, and immature adult polychaetes were challenged with acute (96 hr) doses of No. 2 Fuel Oil or south Louisiana crude oil WSF to test their sensitivity to petroleum hydrocarbons (PHCs). 2. Larvae from all 3 generations, at all exposure concentrations, were no different from control (susceptible) larvae in their sensitivity to the two test oils. F1, F2, and F3 adults exhibited equally increased PHC resistance (X2) compared to control adults. 3. The only evidence of increased resistance beyond that observed in F1 animals was seen in results of bioassays with juvenile worms, wherein PHC resistance increased from slightly below control levels in F1 juveniles to slightly above control tolerance among F3 juveniles. 4. With the exception of F1 worms, removal from chronic exposure 7 or 14 days prior to challenge did not result in termination or reduction of resistance, implicating a genetic mechanism behind PHC resistance in N. arenaceodentata. 5. F3 resistant and unexposed control polychaetes accumulated, metabolized, and excreted a key diaromatic PHC (naphthalene-14C) in quantitatively identical fashion. Mechanisms responsible for resistance appeared unrelated to external permeability and/or excretion rates.

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