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At least 181 records · Page 10Linked to original sources
PubMed1996

Polychaete worms (Annelida) collected in Golfo Dulce, during the Victor Hensen Costa Rica expedition (1993/1994).

A total of forty seven species of benthic polychaetes belonging to twenty five families have been identified from bottom samples taken in Golfo Dulce, Costa Rica, by the RV Victor Hensen. Only those stations collected in waters less than 100 m depth contained polychaetes. The major feeding type of these polychaete species was surface deposit feeding with slightly fewer species recognized as carnivores. Comparison of the species identified from the RV Victor Hensen material with those of the RV. T.V. Thompson material collected in 1969 reveals very few that are common to the two studies, indicating that the polychaetes of Golfo Dulce are probably quite diverse and poorly known. An estimated total of eighty five species of polychaetes have been identified from Golfo Dulce in the two studies.

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↗
PubMed2004

The polychaete Platynereis dumerilii (Annelida): a laboratory animal with spiralian cleavage, lifelong segment proliferation and a mixed benthic/pelagic life cycle.

Platynereis dumerilii, a marine polychaetous annelid with indirect development, can be continuously bred in the laboratory. Here, we describe its spectacular reproduction and development and address a number of open research problems. Oogenesis is easily studied because the oocytes grow while floating in the coelom. Unlike the embryos of other model spiralians, the Platynereis embryo is transparent giving insight into the dynamic structures and processes inside the cells that accompany the prevailing anisotropic cleavages. Functional studies on cell specification and differential gene expression in embryos, larvae, and later stages are underway. Lifelong proliferation of uniform trunk segments qualifies Platynereis as a model for the study of gene expression and of the functional circuitry of this process. Platynereis can also become a stepping stone in the comparison of segmentation between annelids and arthropods because it comes closer to the putative ancestral morphology and style of development than other model annelids.

Animals↗
PubMed2006

Embryogenesis of the serotonergic system in the earthworm Eisenia fetida (Annelida, Oligochaeta): immunohistochemical and biochemical studies.

Organization of the serotonergic system and changes of the serotonin (5-HT) content were studied during the embryogenesis of the earthworm Eisenia fetida, using immunocytochemistry and HPLC. A gradual emergence of 5-HT immunoreactive (IR) cells and their axon projections in the several ganglia of the central (CNS) and peripheral nervous system are described in the context of a staged time-scale of development. The first 5-HT-IR neurons appear in the subesophageal ganglion at an early embryonic stage (E2), followed by neurons in some rostrally located ventral ganglia. In the cerebral ganglion, 5-HT-IR cells can be detected only from stage E5. The number of labeled cells in each ganglion of the embryo increases until hatching, when it is still considerably lower than that observed in adults. This shows that the development of the 5-HTergic system is far from complete by the end of embryogenesis. Organization of 5-HT-IR innervation of the body wall starts by stages E3 to E4. In the stomatogastric nervous system the first 5-HT-IR fibers can be detected by stage E5. By stage E9 5-HT immunopositive neurons can be observed in both the stomatogastric ganglia and the enteric plexus. Both 5-HT levels and the numbers of the labeled cells show a significant increase before hatching, which indicate a functional maturation of the 5-HTergic system. Based on the early appearance of 5-HT, we suppose that it may play a regulatory role in both the gangliogenesis and the maturation of peripheral functions necessary during postembryonic life.

Animals↗
PubMed1994

Trophic exchanges between parent and young during development of Glossiphonia complanata (Annelida, Hirudinea).

Glossiphoniids are iteroparous hirudineans that brood their offspring. The young are attached by the posterior sucker to the parent's ventral side until development is complete. The weight loss of the brooding adults is commonly attributed to their reduced possibility of feeding and to the increased metabolic expense for movements needed to ventilate the offspring. The present study showed that there is a passage of nutritive substrates between the parental body wall and the young's sucker. A possible correlation between this passage and the reabsorption of some muscle fibers that occurs in the adult's body wall is also analyzed.

3-O-Methylglucose↗