摘要:

Surveys of imposex in the dogwhelkNucella lapillussuggest that most parts of the north Atlantic are free of TBT contamination at biologically significant levels. Imposex was absent or poorly developed at the large majority of sites, including coasts adjacent to major shipping lanes passing through Pentland Firth, the Minches and North Channel. There were “hot-spots” of TBT pollution at ports and harbours along the northeast coast of England but, with the exception of the stretch of coast which includes the major ports of Hartlepool and Teesside, impacts were highly localised. The severity of imposex has declined dramatically during the past decade in those areas for which there are comparative data from earlier surveys. This can presumably be attributed to the success of regulations prohibiting the use of TBT-based antifoulants on vessels <25 m in length.

ISSN:0792-4259    

DOI:10.1080/07924259.1998.9652662

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Measures of imposex in the DogwhelkN. lapillusand the Common WhelkB. undatumwere used, together with analyses of butyltins in tissue and sediment samples, to assess current levels of TBT contamination in four sealochs, which are subject to different kinds and intensities of boat use and fish farming. Imposex inN. lapillusis a specific response to TBT and some related organotins and, as would be expected therefore, indices of imposex correlated with concentrations of butyltins in tissues. Data from this species, and sediments, indicate that TBT contamination in three of the sealochs (Loch Sween, Loch Crinan and Killary Harbour) is now low. It has decreased significantly in Loch Sween and Loch Crinan during the past decade. There were higher levels of pollution in Sullom Voe, where oil tankers are a source of TBT. This was reflected in measures of imposex and concentrations of butyltins in tissue samples but not of those in sediments, which were surprisingly low. Imposex was recorded in most samples ofB. undatumexamined in this study but it is not a useful indicator of butyltin contamination. The condition was severe in some places where pollution was low and, conversely, absent or poorly developed in others, where it was high. There was no correlation between the severity of imposex and tissue concentrations of butyltins in this species.

ISSN:0792-4259    

DOI:10.1080/07924259.1998.9652663

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

At metamorphosis the attachment of thePlumatellalarva to the substrate is effected by secretions from glandular cells in the apical plate, the leading pole during swimming. The larval mantle folds back and slides down towards the substrate. By ciliary activity an adhesive secretion is spread over the metamorphosing larva and the attachment area. Two polypides appear through the larval terminal opening. The mantle fold, together with gland cells, nerve cells, sensory cells, and muscle cells from the larva form a nutritive cell mass. Reduction of this nutritive cell mass is accomplished by autolysis and phagocytosis. An invaginated area of the nutritive cell mass is provided with a dense layer of microvilli, which seem to have an absorbtive function. The nutritive cell mass consisting of transitory larval tissues provides a significant source of nutrient for the developing polypide buds.

ISSN:0792-4259    

DOI:10.1080/07924259.1998.9652664

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Within the unpaired testis, spermatogonia, spermatocytes, spermatids and spermatozoa were found. In early spermatids, mitochondria take perinuclear positions and centrioles a diplosomal arrangement. Rootlet-like striated differentiations occur in slightly more advanced stages. Then a conical cytoplasmic projection develops, supported by a single row of closely spaced microtubules. At this stage of maturation, giant Golgi stacks occur within the cytoplasm of the cytophore which is rich in different elongate structures and oval dense bodies. With progressive differentiation, the nucleus elongates and its chromatin condenses into twisted lamellae. Two centrioles, which change their diplosomal configuration and come to lie in line to each other, and rootlet-like structures remain near the tip of the median cytoplasmic outgrowth. Mitochondria start to fuse into a single long cylindrical mitochondrial rod extending beside the lengthening nucleus. Bone-shaped rods, smaller dense sticks and dense bodies migrate into the outgrowth. Spermatozoa are totally ensheathed by cortical microtubules. These tubules show different arrangements along the cell body. The thread-like nucleus extends along the cell, the first quarter excepted, whereas the single mitochondrion extends over two thirds of the cell. Two strings with linearly arranged oval dense bodies run in the median to post-median cell segment; four rows of bone-shaped rods and two rows of smaller electron-dense sticks extend from the frontal end up to the beginning of the last third of the cell. All the different longitudinal cords run in the gaps between 4 sets of microtubules. Ciliary axonemes or lateral bristles were not observed. The present findings substantiate the hypotheses, that spermatozoa in the Macrostomida are aciliate and thatMyozonatakes an isolated position within the Macrostomidae. The occurrence of two centrioles, which come to lie in line to each other and which stay in the tip of the cytoplasmic outgrowth in spermatids, may indicate that biciliate spermatozoa are characteristic for the Rhabditophora (= Macrostomorpha+Trepaxonemata) and not an evolutionary novelty of the Trepaxonemata.

ISSN:0792-4259    

DOI:10.1080/07924259.1998.9652665

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Estradiol from the haemolymph and ovaries of tasar silkworm,Antheraea mylitta, was assayed using radio immunoassay. The estimated concentration of estradiol was 143 pg/mg in the ovaries and 102 pg/ml in the haemolymph.

ISSN:0792-4259    

DOI:10.1080/07924259.1998.9652666

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Reductions in salinity can have adverse effects on larval development and larval survival in some invertebrate taxa but not others. Salinity tolerance of larvae may be particularly important in echinoderms because they are both poor ion regulators and stenohaline. I examined the effect of six levels of salinity (15, 18, 21, 24, 27 and 33 PSU) on survival and rate of development of larvae in the subtropical sea urchinEchinometra lucunter.In the short-term, mortality rate was significantly lower in 33 PSU than in all other salinities except 27 PSU, and it was significantly greater in 15 and 18 PSU than in all higher salinities. In the long-term, daily and cumulative mortality were significantly greater in 15 PSU than in most other salinities over 11 days of development (except for cumulative mortality in 18 PSU). They were significantly greater in 18 PSU than in 21 PSU or 33 PSU over a period of 13 days. Furthermore, daily mortality was significantly greater in 18 PSU than in 24 PSU or 27 PSU at 13 d after fertilization. Daily and cumulative mortality were significantly lower in 33 PSU than in 21, 24 or 27 PSU over a period of 17 days. Although in the control (33 PSU) 75% of larvae completed development to the 8-arm stage at 35 d, no larvae developed further than the 4-arm stage in 18, 21, 24 or 27 PSU; in 15 PSU, ~60% of larvae did not develop further than swimming blastulae. Since prolonged exposure to salinities as high as 27 PSU (frequently recorded in the adult habitat) can result in great larval losses, adaptive behaviours that prevent larvae from entering water layers of low salinity will enhance their chance for survival.

ISSN:0792-4259    

DOI:10.1080/07924259.1998.9652667

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

ISSN:0792-4259    

DOI:10.1080/07924259.1998.9652668

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

ISSN:0792-4259    

DOI:10.1080/07924259.1998.9652669

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

ISSN:0792-4259    

DOI:10.1080/07924259.1998.9652641

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor