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At least 163 records · Page 9Linked to original sources
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↗
PubMed1994

Intermittent swimming in the spermatozoa of the lugworm Arenicola marina (L.) (Annelida: Polychaeta).

Motile spermatozoa of the polychaete Arenicola marina were observed to swim intermittently. On the basis of the behaviour of the flagellum, the quiescent periods can be classified into two main types. The first are those in which, although the generation of the flagellar wave appears to be initiated, its passage down the axoneme appears blocked. This results in the formation of an acute bend (of approximately 2.65 rad) in the proximal region of the flagellum with the remainder of the axoneme remaining straight. These have been termed Type I quiescent periods and are very similar to the "cane-shaped" configuration which has been described in the spermatozoa of some sea urchins. Sperm may also enter a Type II quiescent period, in which both the propagation and the generation of flagellar waves appears blocked. The flagellum of such sperm appears straight or slightly curved and they can remain in this configuration for several minutes. With increased intensity and duration of irradiation, the length of time spent in Type II quiescent period was increased significantly. Both types of quiescent period were (1) reduced in duration and frequency by deletion of calcium from artificial sea water (ASW); (2) either abolished or reduced in duration by the addition of 1 mM cadmium chloride to ASW. In addition, flagellar waveforms very similar to those displayed by spermatozoa in Type I quiescent periods could be induced (if only for a short time) by the addition of the divalent cation ionophore A23187 to ASW.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1983

Syntheses of nucleic acids during spermatogenesis in Nereis diversicolor (annelida polychaeta): a quantitative autoradiographic study.

The development of DNA and RNA synthesis in the germ cell population was studied after a 3H-thymidine or 3H-uridine pulse at each stage of spermatogenesis. The autoradiographic results show that the first sign (after 3 days in vitro) of cellular changes is an increase in RNA synthesis which reaches a maximum at day 5. DNA replication (premeiotic S phase) occurred at day 7, then cells entered meiotic prophase (day 9). Meiotic divisions and spermiogenesis occurred after 11 days. Silver grain counts permit the conclusion that RNA synthesis is clearly higher during premeiotic interphase (days 3-7) than during spermatogonial proliferation (day 0). It appears therefore that male meiotic differentiation in Nereidae is accompanied by increased RNA synthesis.

Animals↗
PubMed1983

Endocrine regulation of spermatogenesis in Nereis diversicolor (annelida polychaeta): experimental study of the control of meiotic differentiation.

In Nereidae, spermatogenesis is regulated by a hormone secreted by the supraesophageal ganglion (brain hormone). The hormonal concentration decreases with worm age. Spermatogonial proliferation in young worms proceeds under a high hormonal level whereas differentiation of spermatozoa in aged worms occurs in the absence of brain hormone. Spermatogonia were removed from the endocrine influence of the brain in vitro by the organ culture method. Isolated parapodia produced spermatozoa after 13 days. Control cultures were obtained by associating a parapodium with the prostomium of a young worm. It seems that the brain hormone inhibits the spermatocyte differentiation since removal of the brain results in increased RNA synthesis, followed by DNA replication, meiosis, and spermiogenesis (Bertout, '83). Modalities of the hormonal control of meiosis, especially at the level of the RNA syntheses related to meiotic differentiation, were investigated. Effects of reintroducing the hormonal influence during meiotic differentiation were studied through parapodium-prostomium associations at various time after the brain inhibition has been lifted. Effects or RNA inhibitors (actinomycin D, alpha-amanitin, cordycepin) were also tested. The results lead us to propose a hypothesis according to which brain hormone would interfere with molecular events related to the transition from the stage of spermatogonial proliferation (mitotic behavior) to the stage of meiotic differentiation (meiotic behavior).

Amanitins↗
PubMed2002

Nucleotide sequences of ribosomal internal transcribed spacers and their utility in distinguishing closely related Perinereis polychaets (Annelida; Polychaeta; Nereididae).

Nucleotide sequences of a segment of the rRNA transcription unit spanning from the 3' end of the 18S rDNA to the 5' end of 28S rDNA were determined for four species of Perinereis polychaetes: P. aibuhitensis, P. floridana, and two undescribed species, Perinereis sp1 and sp2. The 5.8S rDNA sequences are identical among the four species. Intraspecific variability was low with the Kimura 2-parameter (K2P) distance, ranging from 0 to 0.0138 for ITS1 and 0 to 0.0247 for ITS2. The interspecific nucleotide difference was significantly higher than those within species, with a mean K2P of 0.172 for ITS1 and 0.204 for ITS2, suggesting that comparisons of ITS regions can be used to evaluate the phylogenetic relationships among Perinereis species. Both neighbor-joining and parsimony analyses of ITS variability indicate a close relationship between the two undescribed species of Perinereis. These findings highlight the utility of the ITS sequence in conjunction with other morphological and ecological characters to delineate species boundaries among closely related polychaetes.

Journal Article↗