Cad e g c (16 résultats)

12 pp., 2 figs, br. 4.

Assemblages of fossil brachiopods are often characterized by the absence af juvenile specimens. This absence may be due for instance to method of collection, transport by currents, mechanical destruction, diagenetic solution, predation, factors that all may work selectively on small specimens. In some instances, where it was assumed from a taxonomic analysis that these factors could be excluded, low or even absence of juvenile mortality was given as an explanation. These cases are reviewed and alternative explanations are proposed. So, the assemblage could be the result of mass-mortality (census-assemblage) of a population without juveniles due to the fact that this census was taken some time after the last successful recruitment. Another explanation is that adults and juveniles live spatially separated, the assemblage of shells accumulating at localities where the adults live then contains no juvenile specimens. Recent examples of spatial separation of adults and juveniles are given for different groups of marine organisms which shows this phenomenon to be widespread and not only occurring in vagile animals. As long as other explanations are available, low juvenile mortality should be used with great reservation to explain the absence of juveniles in fossil assemblages, as such mortalities are rarely observed in present-day marine animals. Although juvenile mortality is usually high in the planktonic larval stage it is by no means restricted to this stage as stated sometimes. Also just settled benthic organisms are highly vulnerable to predation and other causes of mortality. 29 pp., br. gr. 8.…

During the last few decades nutrient concentrations in the Dutch coastal waters have increased significantly. Values observed for rates of primary production as well as for concentrations of chlorophyll and for particulate organic matter have been higher during recent years than estimates from earlier periods. Thus more food will have been available for herbivorous benthos during recent years. Both biomass and annual production of the macrozoobenthos living on the tidal flats in the western part of the Wadden Sea doubled during the 1970 to 1984 period. More than half of the species contributed to this increase. In the species studied in most detail, Macoma balthica, both reproductive success and growth rate increased significantly during the 15-year period. Though a causal relationship between simultaneous increases of nutrient levels, primary production and secondary production cannot be proved, such a relationship seems to be natural. So far, obvious detrimental effects such as mass mortalities from lack of oxygen appear to be rare in the well-mixed Wadden Sea. 10 pp., 4 figs, gr. 8.…

A large sample rich in empty Bithynia tentaculata (Linnaeus, 1758) was collected in a drift-line along Lake IJssel, The Netherlands. Of 400 adult Bithynia shells 62 (15.5%) showed repair of a damaged outer lip, most probably due to failed attacks by predators. The roach Rutilus rutilus (Linnaeus, 1758) was probably its main shell-crushing predator here. However, repair after physical damage by waves breaking on the stones of the dike cannot be excluded completely. 4 pp., 2 figs, 4. …

10 pp., 4 figs, gr. 8.

Bivalves and gastropods dropped by hooded crows (Corvus corone cornix) show - not surprisingly - a similar fragmentation as those dropped by herring gulls (Larus argentatus). Both bird species drop the shells from some height to crack them. Bivalves have one or both valves fragmented, but the valves still hold together by the ligament. Gastropods have either the spire broken off or a large hole in the body-whorl, sometimes also in the penultimate whorl. This hole is often opposite the aperture leaving the outer lip undamaged. Such large holes seem characteristic for shells dropped by birds. Stomatopods also make holes in shells but these are usually smaller. 5 pp., 2 pls, gr. 8.…

Rissoa membranacea disappeared from the Dutch Wadden Sea together with the large subtidal stands of eelgrass Zostera marina L. in the early 1930s, due to a still not completely understood Wasting disease in Zostera. A small population of R. membranacea survived together with Zostera marina in an inland brackish water de Bol on Texel until 1981. Empty shells of R. membranacea can still be found at these localities. The relatively large size of the top-whorl of Wadden Sea R. membranacea indicates that the larvae were lecithotrophic. In this respect they are comparable to R. membranacea type B from the Roskilde Fjord of Rehfeldt (1968) and Waren (1996) and to R. membranacea s.s. as described by Verduin (1982b). It is, however, questionable whether R. membranacea Type A of Rehfeldt and R. labiosa sensu Verduin can be separated from R. membranacea s.s. They differ only in the smaller size of the embryonic whorl indicating planktothrophic pelagic larvae. This might as well indicate two different types of larval development, lecithotrophic and planktotrophic in one and the same species R. membranacea s.l. Apical dimensions in samples from the Ria de Arosa (Spain) and from Dutch Eemian deposits show a gradual change from small R. labiosa to larger R. membranacea values, which supports the merging of both nominal species and corroborates Waren s suggestion of a continuum in larval development in R. membranacea between lecithotrophy and planktotrophy as well as newer ideas of a gradually and easily crossed transition between lecithotrophy and planktotrophy of McEdward (1997). 10 pp., 2 figs, gr. 8.…

A mass stranding of hundreds of cuttlebones of Sepia orbignyana occurred on the coast of Texel, the Netherlands, in July 2002. Up to now usually only low numbers were found on the Dutch coast. S. orbignyana does not live in the North Sea. Accompanying drift material such as thong weed Himanthalia elongata indicates a SW origin from the Channel and skeletons of the By-the-wind-sailor Velella velella (Cnidaria, Hydrozoa, Chondrophora) may even indicate an origin from as far as the Bay of Biscay. Drift-bottle experiments in the past have indicated that it takes at least one to two months to drift from the entrance of the Channel near Plymouth to the Dutch coast. A large proportion of the cuttlebones (65%) showed peck marks by fulmars and 55% had scratch marks probably also made by birds supporting a drifting time of this length. 8 pp., 5 figs, gr. 8.…

In this paper we report on oystercatchers feeding on Corbicula fluminea, a recent invader in the river Rhine. Oystercatchers are specialised molluscivores. They could reach these freshwater bivalves during low river level in the summer of 2003 and in the end of March 2004. The shell remains after consumption have a characteristic damage pattern: the valves still adhere by the ligament and only one of the valves has a (small) piece broken off ventrally. Due to lack of access, oystercatchers cannot use this food source on a regular base as they can with mussels and cockles in tidal areas exposed every low tide. Feeding irregularly on Corbicula shows the oystercatcher s flexibility in food choice. 4 pp., 1 fig., gr. 8.…

Littorina littorea shells found broken on a cycle-track next to where they lived, are thought to be broken by shell-dropping birds. Shells broken experimentally by dropping them from 6 m height on a concrete floor showed very similar damage: a hole in the last whorl, whereas the aperture rim remained intact. Examples from the literature indicate this shell damage to be characteristic for shell-dropping by birds. We suspect carrion crows as the culprit, but field observations have to prove this. 4 pp., 3 figs, gr. 8.…

24 pp., 7 figs, 4.

Soft cover. Etat : New. Language:Chinese.Author:QUAN GUO CAD JI NENG DENG JI PEI XUN GONG ZUO ZHI DAO WEI YUAN HUI ZHI DING.Binding:Soft cover.Publisher:Standards Press of China.

Kuiper, H.: De Nederlandse Malacologische Vereniging, vijfenzeventig jaar. Coomans, H. E. & Moolenbeek, R. G.: Het Zo?logisch Museum Amsterdam en de Nederlandse Malacologische Vereniging. Gittenberger, E.: s Rijks Museum van Natuurlijke Historie, het Nationaal Natuurhistorisch Museum, Naturalis, en de Nederlandse Malacologische Vereniging. Meijer, T.: De geschiedenis van het molluskenonderzoek bij de Rijks Geologische Dienst. Janssen, A. W.: De fossielenatlas : meer dan 50 jaar historie . de mensen, de feiten. Boekschoten, B.: Weke dieren, strakke schelpen. van Dijk, A.: Fossielen uit de frontlijn. van der Velde, G.: Malacologisch onderzoek aan de Radboud Universiteit in Nijmegen. Joosse, J.: Het slakkenonderzoek aan de Vrije Universiteit 1956-1995. Breure, B. & van Bruggen, D.: Collecties, veldwerk en onderzoek aan tropische landslakken: Nederlandse bijdragen gedurende m??r dan 75 jaar. Meyling, A. G. & de Bruyne, R.: Het Atlasproject Nederlandse Mollusken (ANM). van Bruggen-Gorter, W.: Slakken ? la carte. Ervaringen van een aanvankelijke buitenstaander. van Bruggen, D. & Kuiper, H.: De Nederlandse Malacologische Vereniging: twee crises in vijfenzeventig jaar. Vervoort, W.: Jeugdzonden. Backhuys, W.: Drie zeldzame Nederlandstalige publicaties over Nederlandse Mollusken. Faber, W., Breure, B. & Buijs, J. P.: Een geslaagd huwelijk: de fusie van NMV en BM. Gulden, G., Faber, W., Kemperman, T. & van Dorp, R.: Schelpenbeurs en symposium. Piersma, T., Kraan, C. & Dekinga, A.: Hoe het nonnetje verdween uit de Waddenzee. Wijnhoeven, S., Hummel, H. & Escaravage, V.: Ruim 50 jaar mollusken onderzoek in de Delta. Ontwikkelingen in het onderzoek aan het NIOO-CEME en zijn voorlopers. Cad?e, G. C.: Mollusken onderzoek op het Zo?logisch Station (later NIOZ). ten Hallers-Tjabbes, C.: Tien jaar van slak tot verdrag. Smaal, A. C.: De historie van toegepast schelpdieronderzoek in Nederland. Karnekamp, C.: Hoe ik schelpengek werd. Dijkstra, H. H.: Pectinidae, het bekijken en verzamelen waard. Kuijper, W.: 50 jaar schelpen. Lever, J.: Experimenteel onderzoek naar de wetmatigheden bij het aanspoelen van schelpen. Lever, B.: Drie generaties Lever in de NMV. van Pel, P.: Het ontstaan en het verzamelen van de collectie Piet van Pel. Leiden. 144 pp., num. color figs, hardcover 4.…

paperback. Etat : New. Paperback. Pub Date: 2022-07-01 Pages: 394 Language: Chinese Publisher: Higher Education Press Descriptive Geometry and Water Conservancy Engineering Drawing (7th Edition) According to the Ministry of Education Engineering Graphics Course Teaching Guidance Subcommittee 2019 The Basic Requirements for the Teaching of Engineering Graphics Courses in Colleges and Universities formulated in 2009 was revised on the basis of the sixth edition in combination with the achievements of teaching reform .…

Soft cover. Etat : New. Language:Chinese.Author:ZHONG GUO JIAN ZHU KE XUE YAN JIU YUAN PKPM CAD GONG CHENG BU.Binding:Soft cover.Publisher:Chinese construction industry; 1 (May 1. 2008).

paperback. Etat : New. Pub Date :2006-12-01 Publisher: China Machine Press book is a selection of nearly 100 works of the 2006 inaugural three-dimensional mathematical modeling contest . is divided into two parts creative papers and design works covering the automotive. aviation . consumer electronics. and mechanical and electrical products and other industries involving ProENGINEER. UG. SolidEdge. SolideWorks. Alias. CATIA dozen the 3D functional design and industrial software. is the first the write CAD and CAID .…