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At least 199 records · Page 11Linked to original sources
PubMed2005

Bipolar head regeneration induced by artificial amputation in Enchytraeus japonensis (Annelida, Oligochaeta).

The Enchytraeida Oligochaeta Enchytraeus japonensis propagates asexually by spontaneous autotomy. Normally, each of the 5-10 fragments derived from a single worm regenerates a head anteriorly and a tail posteriorly. Occasionally, however, a head is formed posteriorly in addition to the normal anterior head, resulting in a bipolar worm. This phenomenon prompted us to conduct a series of experiments to clarify how the head and the tail are determined during regeneration in this species. The results showed that (1) bipolar head regeneration occurred only after artificial amputation, and not by spontaneous autotomy, (2) anesthesia before amputation raised the frequency of bipolar head regeneration, and (3) an extraordinarily high proportion of artificially amputated head fragments regenerated posterior heads. Close microscopic observation of body segments showed that each trunk segment has one specific autotomic position, while the head segments anterior to the VIIth segment do not. Only the most posterior segment VII in the head has an autotomic position. Examination just after amputation found that the artificial cutting plane did not correspond to the normal autotomic position in most cases. As time passed, however, the proportion of worms whose cutting planes corresponded to the autotomic position increased. It was suspected that the fragments autotomized after the artificial amputation (corrective autotomy). This post-amputation autotomy was probably inhibited by anesthesia. The rate at which amputated fragments did not autotomize corresponded roughly to the rate of bipolar regeneration. It was hypothesized then that the head regenerated posteriorly if a fragment was not amputated at the precise autotomic position from which it regenerated without succeeding in corrective autotomy.

Animals↗
PubMed2004

Trochophora larvae: cell-lineages, ciliary bands, and body regions. 1. Annelida and Mollusca.

The trochophora concept and the literature on cleavage patterns and differentiation of ectodermal structures in annelids ("polychaetes") and molluscs are reviewed. The early development shows some variation within both phyla, and the cephalopods have a highly modified development. Nevertheless, there are conspicuous similarities between the early development of the two phyla, related to the highly conserved spiral cleavage pattern. Apical and cerebral ganglia have almost identical origin in the two phyla, and the cell-lineage of the prototroch is identical, except for minor variations between species. The cell-lineage of the metatrochs is almost unknown, but the telotroch of annelids and the "telotroch" of the gastropod Patella originate from the 2d-cell, as does the gastrotroch in the few species which have been studied. The segmented annelid body, i.e. the region behind the peristome, develops through addition of new ectoderm from a ring of 2d-cells just in front of the telotroch. This whole region is thus derived from 2d-cells. Conversely, the mollusc body is covered by descendants of cells from both the C and D quadrants and a growth zone is not apparent. This supports the notion that the molluscs are not segmented like the annelids, and that the repeated structures seen in polyplacophorans and monoplacophorans do not represent a segmentation homologous to that of the annelids.

Animals↗
PubMed2004

Nephridial and gonoduct distribution patterns in Nerillidae (Annelida: Polychaeta) examined by tubulin staining and cLSM.

The distribution and configuration of nephridia and gonoducts are described for seven species from seven genera of the interstitial polychaete family Nerillidae. The ciliated nephridia and gonoducts were identified by tubulin staining and examined with a confocal laser scanning microscope. The following species of the seven to nine-segmented nerillids were examined: Leptonerilla prospera, Nerilla antennata (nine segments); Nerillidium mediterraneum, Trochonerilla mobilis, Gen. sp. A (eight segments); and Aristonerilla brevis, Paranerilla limicola (seven segments). Two of the examined species are hermaphroditic (N. mediterraneum and Gen. sp. A). Segmented nephridia can be found from the first to the last segment, with a total of two to five pairs. One to three pairs of segmented spermioducts are present in all species. One pair of gonoducts is found in all species, except for P. limicola, where they are absent. Nephridia vary in length from half to almost twice the length of a segment and may be curled up in loops. In A. brevis and P. limicola the nephridia are discontinuously ciliated. The distribution and configuration of spermioducts and gonoducts are also variable, although to a lesser extent. The spermioduct distribution is generally consistent within genera and therefore of systematic significance. Nephridia and gonoducts are never found together in the same segments, and the results indicate that gonoducts and nephridia have developed from the same anlagen. The distribution patterns of nephridia and gonoducts are discussed with respect to segmentation, systematics, and development.

Animals↗
PubMed2005

Clonal domains in postlarval Platynereis dumerilii (Annelida: Polychaeta).

Following an enzymatic procedure for softening the egg envelope, blastomeres in the embryo of the polychaete Platynereis dumerilii were injected with TRITC-dextran. Injection was successful in the following blastomeres: AB, CD, A, B, C, D, 1a-1d, 1A-1D, 4d, and 4d(1). The distribution of fluorescent label was recorded by confocal laser scanning microscopy of young, three-segmented worms after 3 or 4 days of development, in some cases also in 1-day-old trochophore larvae. Results were documented by single optical sections, by stacking a limited number or a complete set of optical sections, and by computer-generated surface views of both the labeled tissue domains and the body contours from complete image stacks of whole worms. With respect to their descent from the embryonic cell pattern, five major compartments can be distinguished which together compose the body of the young worm: 1) The epispheric, epidermal, and neural region of the head, composed of four domains arranged as quasi-radial sectors derived from micromeres 1a, 1b (left and right ventral), and 1c and 1d (right and left dorsal). 2) A posttrochal epidermal region of the head originating from micromeres 2a(1)-2c(1) and constituting the ventral and lateral posttrochal epidermis of the head. 3) A stomodeal-ectomesodermal region of the head, including the stomodeum (micromeres 2a(2) and 2c(2)), its mesodermal envelope, and head mesoderm (micromeres 3a-3d). 4) A solid cone composed of the four terminal macromeres 4A-4D, forming the core of the trunk as the endoderm anlage. 5) An epidermal and mesodermal coating of the trunk originating from the dorsal micromeres 2d and 4d. The region of the so-called (first, anterior) peristomial cirri at the posterior flanks of the head is also composed of 2d- and 4d-derived trunk tissue, thus corroborating the postulated descent of this region and its appendages from a cephalized anteriormost trunk segment and its parapodia. The cell-lineage domains of the first and third micromere tiers are arranged left or right of the sagittal plane, while two micromeres of the second quartet are in a lateral and, initially, two in a median position (2b ventral and 2d dorsal). The offspring of micromere 2d expand from a dorsal position toward the ventral midline and those of cell 4d from a posterior-dorsal site toward the anterior, initially forming two lateral bands. In the epispheric part of the head, part of the neurectodermal tissue derived from micromeres 1a and 1b interweaves in a medio-sagittal bar, and part of the first micromere offspring of all four quadrants (1a-1d) combine in forming a central brain neuropil. Each of the latter sends neurites through both of the circumesophageal connectives. Paired muscle tracts extend through the head toward the base of the antennae and are probably derived from micromeres 3a and 3b. A mesodermal envelope of the stomodeum is probably built by the 3c and 3d micromeres. The formation of symmetry and the nature of the body axes in the embryo and adult of Platynereis dumerilii are discussed. J. Morphol.

Animals↗
PubMed2005

Oogenesis in the leech Glossiphonia heteroclita (Annelida, Hirudinea, Glossiphonidae). I. Ovary structure and previtellogenic growth of oocytes.

Glossiphonia heteroclita has paired ovaries whose shape and dimensions change as oogenesis proceeds: during early previtellogenesis they are small and club-shaped, whereas during vitellogenesis they broaden and elongate considerably. During early oogenesis (previtellogenesis), each ovary is composed of an outer envelope (ovisac) that surrounds the ovary cavity and is filled with hemocoelomic fluid, in which a single and very convoluted ovary cord is bathed. The ovary cord consists of germline cells, including nurse cells and young oocytes surrounded by a layer of elongated follicle cells. Additionally, follicle cells with long cytoplasmic projections occur inside the ovary cord, where they separate germ cells from each other. The ovary cord contains thousands of nurse cells. Each nurse cell has one intercellular bridge, connecting it to a central anucleate cytoplasmic mass, the cytophore (rachis); it in turn is connected by one intercellular bridge with each growing oocyte. Numerous mitochondria, RER cisternae, ribosomes, and Golgi complexes are transported from the nurse cells, via the intercellular bridge and cytophore, to the growing oocytes. Oogenesis in G. heteroclita is synchronous with all oocytes in the ovary in the same stage of oogenesis. The youngest observed oocytes are slightly larger than nurse cells, and usually occupy the periphery of the ovary cord. As previtellogenesis proceeds, the oocytes gather a vast amount of cell organelles and become more voluminous. As a result, in late previtellogenesis the oocytes gradually protrude into the ovary cavity. Simultaneously with oocyte growth, the follicle cells differentiate into two subpopulations. The morphology of the follicle cells surrounding the nurse cells and penetrating the ovary cord does not change, whereas those enveloping the growing oocytes become more voluminous. Their plasma membrane invaginates deeply, forming numerous broad vesicles that eventually seem to form channels or conducts through which the hemocoelomic fluid can easily access the growing oocytes.

Animals↗
PubMed2006

External sense organs in freshwater oligochaetes (Annelida, Clitellata) revealed by scanning electron microscopy.

Freshwater oligochaetes have at least two kinds of external sense organs: multiciliate organs of short cilia (also present in earthworms) and sense organs with one to three long cilia (unknown in earthworms and possibly acting as rheoreceptors). Ciliate sense organs of freshwater oligochaetes are distributed over their entire body surface, including the clitellum. They are scattered on the prostomium and pigidium and are arranged into a transversal chaetal row and dispersed or forming a few other discrete transversal rows on chaetal segments. Three species display very prominent sense organs (sensory buds in Protuberodrilus tourenqui and papillae in Ophidonais serpentina and Spirosperma velutinus). The number of cilia per organ at the prostomium of freshwater families appears to be fewer than that of terrestrial ones. It is suggested that the total number of cilia at the prostomium of the freshwater species could be related to their habitat, evolving from an epibenthic to an endobenthic way of life.

Animals↗
PubMed2007

Structure of the vector tissue in piscicolid leeches (Annelida, Hirudinea, Rhynchobdellida, Piscicolidae).

Hypodermic insemination occurs in piscicolid leeches (Hirudinea, Rhynchobdellida, Piscicolidae). The spermatophore is implanted in a specialized region of the leech body, the copulatory area. Just beneath the copulatory area, there is a specialized connective tissue (vector tissue) that is considered to guide the sperm toward the ovaries. In this study, we show that the vector tissue in the four species of the genus Piscicola is composed of a mass of cells located directly beneath the copulatory area, and two thin strands extend toward the ovaries. The ultrastructure of the vector tissue has been described for the first time. Four cell types were identified, constructing the vector tissue. The envelope of this tissue is made up of extracellular fibrous matrix and two types of cells: vesicular and flat envelope cells, which are embedded within the matrix. The rest of the tissue is formed of granular and plasmatic cells. Both of these last cell types have prominent cytoplasmic projections, filled with a filamentous material. However, only granular cells have numerous small electron-dense granules in their cytoplasm. The vector tissue was described prior, during and following copulation. Sperm passes within free spaces between the granular and plasmatic cells. Characteristic vector tissue cells also occur within the ovary wall and inside the ovary lumen. This supports earlier data, which postulated that the vector tissue appears to be an outgrowth of the ovary wall.

Animals↗
PubMed1988

Ultrastructure of the anterior salivary gland cells of the giant leech, Haementeria ghilianii (Annelida, Hirudinea).

The giant anterior salivary gland cells from the large mammalian blood-sucking, glossiphoniid leech, Haementeria ghilianii, can be subdivided into three morphologically and functionally distinct regions: 1) a soma, responsible for the synthesis and storage of secretory products; 2) a long cell process, responsible for the storage and intracellular transport of the secretory vesicles; and 3) the site of exocytosis at the process terminal. The giant somata are densely packed with secretory vesicles. Deep plasmalemmal invaginations invade the soma and form an extensive system of extracellular lacunae. The rough endoplasmic reticulum (ER) and the Golgi apparatus are organized in the cell periphery, near the highly branched nucleus, and along the lacunae. The somata taper into long processes extending over several centimeters to the proboscis tip. These contain secretory vesicles through their whole length. In the process periphery, the vesicles are completely ensheathed by a concentric subplasmalemmal smooth ER cisterna. This originates deeply within the soma and extends through the whole cell process to its terminal. The ER provides support for up to several hundred longitudinally oriented microtubules. Secretion occurs at the very tip of the cell processes, each of which terminates at the proboscis tip at the base of a cuticular pore. We found synapses close to the sites of exocytosis, providing morphological evidence for neuronal control of secretion.

Animals↗
PubMed2001

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.

Animals↗
PubMed1994

A PCR-based survey of homeobox genes in Ctenodrilus serratus (Annelida: Polychaeta).

The polychaete worm Ctenodrilus serratus was surveyed for the presence of HOM/HOX and engrailed-type homeobox genes using PCR with degenerate primers. Sixteen unique homeobox fragments were found in surveys of genomic and cDNA with three different primer sets. For three fragments, RACE was employed to obtain additional homeobox sequence and the 3' flanking region. Nine HOM/HOX-type fragments were identified, including putative representatives of the Hox1/lab, Hox2/pb, Hox3, Hox4/Dfd, and Antp/Lox5 cognate groups. Two additional Antp-like fragments could not be assigned specific orthology. Presence of an ortholog of leech Lox2 in addition to a Ubx/abdA-like gene suggests that independent duplications of a single precursor occurred in the annelid and arthropod lineages. No representative of the Hox9/AbdB group was identified. Our results are consistent with a hypothesis of a single HOM/HOX cluster in Ctenodrilus as extensive as that seen in strongly tagmatized arthropods, suggesting that the primitive role of these genes even in overtly metameric animals was something other than specification of overt segmental differentiation. The primers used also detected representatives of six other homeobox classes or families: Xlox (XlHbox8/HTr-A2), Ovx (Chox7), caudal, Prh (proline-rich homeobox), NEC (ceh-9/Tghbox5), and engrailed.

Amino Acid Sequence↗
PubMed1994

HOM/Hox-type homeoboxes from Stylaria lacustris (Annelida: Oligochaeta).

The polymerase chain reaction was used to survey the oligochaete worm Stylaria lacustris for HOM/Hox type homeobox genes. Twelve fragments were identified and in most cases were assignable to cognate groups on the basis of amino acid similarity. Stylaria appears to have three labial-type genes, a HOX B3 cognate, several genes similar to Antennapedia, and cognates of Abdominal-B and CHox7.

Amino Acid Sequence↗
PubMed1999

Higher level relationships of leeches (Annelida: Clitellata: Euhirudinea) based on morphology and gene sequences.

The evolutionary patterns of divergence of seven euhirudinean families were investigated by cladistic analysis of 33 euhirudinean species. Oligochaetes, Acanthobdella peledina, and branchiobdellidans were included as outgroup taxa. Cladistic analysis employed 1.8 kb of nuclear 18S ribosomal DNA and 651 bp of mitochondrial cytochrome c oxidase subunit I in addition to morphological data. The use of two molecular data sets, one nuclear gene and one mitochondrial gene, as well as morphological data combined historical information evolving under a variety of different constraints and therefore was less susceptible to the biases that could confound the use of only one type of data. Results suggest that the nuclear 18S rDNA gene yields a meaningful historical signal for determining higher level relationships. The more rapidly evolving CO-I gene was informative for recent or local areas of the evolutionary hypothesis, such as within-family relationships. Analyses combining all data from the three character sets yielded one most-parsimonious tree. Most of the higher taxa in recent leech systematics were well corroborated in the resulting topology. However, these results suggested paraphyly of the order Rhynchobdellida, which contradicts the presence of a proboscis as a synapomorphy. The medicinal leech family Hirudinidae was polyphyletic because Haemadipsidae and Haemopidae each have a hirudinid ancestor. In addition, all but one of the genera within the family Erpobdellidae must be either abandoned or renamed. Unusual findings included compelling evidence of historical plasticity in bloodfeeding behavior, having been lost at least four times in the course of euhirudinean evolution. Biogeographic patterns supported a New World origin for Arhynchobdellida.

Animals↗
PubMed2000

Phylogenetic analysis of Tubificidae (Annelida, Clitellata) based on 18S rDNA sequences.

Tubificids are aquatic clitellate worms, but recent analyses of morphological characters suggested that this family, as currently recognized, is paraphyletic. Sequences of the 18S rDNA gene of 40 protostome worm species (including 13 representatives of the Tubificidae) and 2 mollusc species were cladistically analyzed to test the monophyly of the Tubificidae and that of some of its constituent subfamilies. Under all alignments tested, the same general phylogenetic pattern emerged. The data support the idea that the Naididae, another clitellate taxon, is associated with some "rhyacodriline" groups within the Tubificidae. The data also corroborate the idea that the Tubificinae and the Limnodriloidinae are monophyletic but indicate that the Rhyacodrilinae and the Phallodrilinae are not. Bathydrilus does not appear to be closely related to other "phallodriline" genera.

Animals↗
PubMed1994

Characterization of connectin-like proteins of obliquely striated muscle of a polychaete (Annelida).

In obliquely striated muscle of polychaete, Neanthes sp., three kinds of connectin (titin)-like high molecular weight proteins, approximately 4000 kDa, approximately 1200 kDa and approximately 700 kDa, were detected by SDS gel electrophoresis and immunoblots using antibodies to vertebrate skeletal muscle connectin and antiserum to the protein in question. The 700 kDa protein was isolated and characterized as a beta sheet-rich filament 170 nm long and 4 nm wide. Using polyclonal antibodies to the 700 kDa protein, the binding of the immunogold to the thick filament was only demonstrated in high ionic strength relaxing solution which solubilized some myosin. This observation suggested that the 700 kDa protein was localized below the layers of myosin in the thick filament and this localization is different from that of twitchin of C elegans bodywall muscle that is on the surface of thick filament. The 4000 kDa protein was identified as a very thin filament linking the thick filament to the dense body. The very thin filaments were visualized in gelsolin-treated actin filament-free fibres. The 1200 kDa protein was located in the periphery of the dense body. A model of the elastic filament in polychaete bodywall muscle is presented.

Actin Cytoskeleton↗
PubMed1996

Effects of platinum (Pt4+) on Lumbriculus variegatus Müller (Annelida, Oligochaetae): acute toxicity and bioaccumulation.

The acute toxicity and bioaccumulation (rates, kinetic) of tetravalent platinum in Lumbriculus variegatus under different physicochemical conditions (temperature and total water hardness) were investigated. Increased Pt4+ concentration (from 0.05 to 50 mg/L), exposure (up to 30 days), temperature (from 4 to 20 degrees C) and decreasing water hardness (from 300 to 0 mg/L CaCO3) increased Pt toxicity. The metal accumulated at a constant rate that was concentration, temperature and time dependent. The median lethal concentration (96h LC50) varied greatly from 0.397 mg/L in distilled water to 30 mg/L in the hard water from Champagne. Thus, L. var. can tolerate high levels of Pt. As a result, L. var. can be used in the laboratory to analyze mechanisms of adaptation to the induced stress and in the field as an indicator of Pt pollution.

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↗
PubMed1989

The effect of lead incorporation on the elemental composition of earthworm (Annelida, Oligochaeta) chloragosome granules.

The elemental compositions of chloragosome 'granules' in the earthworm Lumbricus rubellus living in non-polluted (Dinas Powys) and heavily Pb-polluted (Wemyss) soils were determined by fully quantitative electron probe X-ray microanalysis. P, Ca, S and Zn were the major elemental components of the chloragosomes. High Pb concentrations were found in chloragosomes of Wemyss animals; Pb was not detected in chloragosomes of Dinas Powys animals. Partial correlation and regression analysis indicated that the in vivo accumulation of Pb by chloragosomes was accompanied by diminished chloragosomal Ca concentrations. Pb is bound by P-containing ligand(s) in the chloragosome matrix. The sequestration of Pb by chloragosomes results in the detoxification of the metal by accumulative immobilization.

Animals↗