Search results for "Crust"
showing 10 items of 599 documents
A hidden species becoming visible : biogeography and ecology of Rhynchotalona latens (Cladocera, Anomopoda, Chydoridae)
2019
A long hidden chydorid (Chydoridae, Cladocera) taxon, first found as fossil specimens and recently redefined as Rhynchotalona latens (Sarmaja-Korjonen et al., Hydrobiologia 436: 165-169, 2000) is investigated for its biogeography and ecology. Late Holocene sediment sequence from Lake Sylvilampi, NE Finnish Lapland, and R. latens spatial distribution in relation to limno-climatic attributes in Finland were examined. Principal component analyses of fossil cladoceran communities showed that R. latens is mostly affiliated with Alonella excisa-Alonopsis elongata-Alonella nana species pool. Generalized linear modeling of R. latens responses to limno-climatic variation indicated that it prefers ac…
Morphometry of microstromatolites in calcrete laminar crusts and a fractal model of their growth
1996
The laminar crust, constituting the upper part of calcretes (terrestrial CaCO3 accumulations inside surficial sediments), is a succession of thin layers of various colors and shapes resembling micro-stromatolites. The crust structure and its diagenetic evolution are similar to stromatolites. A quantitative study of its structure was made using image analysis. Euclidian parameters were calculated to describe lamina shape. Eight hundred and eighty-six laminae were divided into six classes from the flatest forms to columnar shapes. The geometrical relationships between the shapes are interpreted as steps in the growth process of the microstromatolite. A fractal model of laminar crust growth wa…
Cuticle: Formation, Moulting and Control
1984
The relative rigidity of the arthropod exoskeleton makes it impossible for body size to increase continuously during the postembryonic development of these animals. Once they have hatched from the egg, they grow in steps, passing through a variable number of (larval) stages (Fig. 1 a). Apart from a few exceptions, there are between 3 and 10 such stages in the arachnids, 3–20 in the crustaceans, and 3–10 in the insects. In many cases a metamorphosis stage intervenes (some crustaceans; holometabolous insects) (Fig. 9b, c).
Factors affecting abundance of Triaenophorus infection in Cyclops strenuus, and parasite-induced changes in host fitness.
2000
Factors affecting the abundance of Triaenophorus crassus and Triaenophorus nodulosus procercoids in their copepod first intermediate host, Cyclops strenuus, and effects of infection on feeding behaviour, reproduction and survival of the host were studied experimentally. When exposed to the same number of coracidia, copepods harboured considerably less procercoids in the trials where ciliates or Artemia salina nauplii were given as alternative food items. The prevalence of infection was higher in adult copepods as compared with copepodite stage IV and stage V, and higher in stage V than in stage IV. The prevalences in adult females and males did not differ significantly from each other. The …
New data on the early development of Hysterothylacium aduncum (Nematoda, Anisakidae).
1998
This note reports on incidental observations of the early development of the third-stage larvae of Hysterothylacium aduncum from gadid fishes. Gravid H. aduncum females were collected from Pollachius virens, Pollachius pollachius. Gadus morhua, and Molva molva in Norwegian waters. The eggs were incubated at 20 per thousand salinity and 5 C. Spontaneous hatching of third-stage larvae was observed 10-25 days after egg deposition. These larvae were long lived and could infect Acartia tonsa copepods, the infections being maintained for up to 34 days. The morphology of the third-stage larvae in the copepods and some traits of the life cycle were similar to those reported in previous studies. How…
Potential predation pressure of littoral mysids on herring (Clupea harengus membras L.) eggs and yolk-sac larvae
2008
The predation potential of littoral mysid shrimps (Mysidacea) on Baltic herring (Clupea harengus membras L.) eggs and yolk-sac larvae was studied experimentally. The results showed that littoral mysids feed actively on both eggs and yolk-sac larvae. It was shown that Neomysis integer preys on eggs, which are not attached to the substrate. Alternative food (yolk-sac larvae or zooplankton) did not decrease feeding rate on eggs. Only gravel as a bottom material lowered the ingestion rate to nearly zero. The largest of the mysid species Praunus flexuosus ate yolk-sac larvae more than other mysids and most efficiently. Mysids switched to feed on eggs when larvae and eggs were offered simultaneou…
Shear heating induced lithospheric-scale localization: Does it result in subduction?
2012
Abstract Even though it is a well-established fact that the Earth is currently in a plate-tectonics mode, the question on how to “break” lithospheric plates and initiate subduction remains a matter of debate. Here we focus on shear heating as a potential mechanism to cause lithospheric shear localization and subsequent subduction initiation in oceanic plates. It is shown that shear heating under some conditions (i) facilitates the formation of a lithospheric-scale shear zone and (ii) is capable of stabilizing a lithospheric-scale shear zone, thus creating the necessary condition for subduction initiation to occur. Furthermore, we demonstrate that not only the localization process is of impo…
Melt production, redistribution and accumulation in mid-crustal source rocks, with implications for crustal-scale melt transfer
2014
Abstract Ascent of granitic melt initiates under suprasolidus conditions in the mid- to lower crust before continuing through subsolidus rocks to higher crustal levels. Whereas migration of melt in suprasolidus rocks can occur in pervasive net-like structures and involve relatively small melt volumes, ascent through the subsolidus crust requires more focused, dyke-like structures and larger volumes to prevent freezing. Migmatites in the Aus granulite terrain, southern Namibia, preserve evidence that large-scale melt redistribution and accumulation occurred in the near-source region under suprasolidus conditions. Melt that was mainly produced in metapelitic rocks utilised pervasive small-sca…
Light-mediated host searching strategies in a fish ectoparasite, Argulus foliaceus L. (crustacea: branchiura).
2000
Argulus foliaceus, an obligate fish ectoparasite, can search for its hosts in both light and dark conditions and uses vision in the light. We have examined what searching mode is used at night, when the infection rate was at its highest, and which stimuli produced by the fish are most important. A change of illumination produced a clear difference in the searching behaviour of adult Argulus females. The mean swimming speed and the area explored were 3-4 times higher in the dark, when the parasite employed a cruising search strategy. This changed to an ambush (hover-and-wait) strategy in the light. The swimming activity is accompanied by changes in metabolic costs; the activity of the electr…
Molecular phylogeny of the Notostraca
2012
Abstract We used a combined analysis of one nuclear (28S rDNA) and three mitochondrial markers (COI, 12S rDNA, 16S rDNA) to infer the molecular phylogeny of the Notostraca, represented by samples from the six continents that are inhabited by this group of branchiopod crustaceans. Our results confirm the monophyly of both extant notostracan genera Triops and Lepidurus with good support in model based and maximum parsimony analyses. We used branchiopod fossils as a calibration to infer divergence times among notostracan lineages and accounted for rate heterogeneity among lineages by applying relaxed-clock models. Our divergence date estimates indicate an initial diversification into the gener…