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  • 1
    Electronic Resource
    Electronic Resource
    Thermal preferences in upstream migrating glass-eels of Anguilla anguilla (L.) (1986)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 28 (1986), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The effect of temperature on the migratory behaviour of European glass-eels, Anguilla anguilla, during the first stages of their ascent into inland waters has been investigated. Very little research has documented the thermal preferences of glass-eels, most being directed instead to the study of their thermal resistance and survival. The experimental method adopted aimed at acquiring information on short- and long-term thermal choices and sought to provide evidence of the influence of preceding experiences on choices made during the tests. The results obtained in short-term choices (acute preferendum tests) show a clear preference for flows of water at temperature equal to acclimation temperature rather than for flows at temperatures lower or higher by 3° C. It is sufficient for the glass-eels to remain for about 1 h at a different temperature (acclimation temperature ± 3–4°C) for their subsequent choices to be influenced. When choosing between flows warmer or colder than acclimation water, glass-eels prefer the lower temperature. When the temperature presented is very low (about 3° C) the preference is inverted. There is evidence that the temperature gradient represents one of the main orienting cues. In long-term choices (final preference tests) the experimental apparatus allowed prolonged observation (from 24 to 52 h) of the choices between three shelters, the only difference between these being their internal temperatures. In this situation the glass-eels show a clear preference for temperatures higher than that of the environment. For both intervals of environmental temperature considered (11.0–12.6°C and 14.3–17.3° C) a linear correlation exists between temperature difference and number of choices made for the shelters at higher temperatures. The number of glass-eels choosing a higher temperature is greater in the case of lower environmental temperature. In acute preference tests the thermal stimulation is added to a rheotactic response. The glass-eels find themselves in an analogous situation to that during the ascent. On the other hand, in the second experimental situation the choices are an expression of a pure thermal preference.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1986.tb05186.x
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  • 2
    Electronic Resource
    Electronic Resource
    Spectral sensitivity in a fresh-water Gastrotrich (Lepidodermella squamatum Dujardin) (1980)
    Springer
    Cellular and molecular life sciences 36 (1980), S. 830-831 
    Details
    ISSN: 1420-9071
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Confronted with a series of alternative choices between environmental lights of different wavelengths,Lepidodermella squamatum Dujardin (Gastrotricha) shows a selective sensitivity towards coloured lights, especially blue, in preference to white light.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01978596
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Nuclear DNA content in Gastrotricha (1995)
    Springer
    Cellular and molecular life sciences 51 (1995), S. 356-359 
    Details
    ISSN: 1420-9071
    Keywords: Gastrotricha ; DNA content ; genome size
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract A cytofluorometric evaluation of nuclear DNA content was carried out on fifteen species of Gastrotricha. Genome size, ranging from 0.05 to 0.63 pg, appears uniform in this group and rather low compared to values found in other lower Metazoa. Differences in DNA content between the two orders of the phylum, Macrodasyida and Chaetonotida, which differ greatly in morphology and reproductive biology, are not evident. From these data, a polyploid condition of obligatory parthenogenetic Chaetonotida seems unlikely.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01928894
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  • 4
    Electronic Resource
    Electronic Resource
    Morphology of the reproductive system and spermatozoa of Mesodasys adenotubulatus (Gastrotricha: Macrodasyida) (1999)
    Springer
    Marine biology 135 (1999), S. 515-520 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Mesodasys adenotubulatus Hummon, Todaro and Tongiorgi 1993 is a simultaneous hermaphrodite. Two club-shaped testes extend along the sides of the anterior intestine and show spermatogenetic stages maturing in a caudo-cephalic and centripetal direction. Sperm ducts join together dorsally to the intestine before opening into a pear-like caudal organ. An unpaired, dorsal ovary lies anteriorly to the confluence of sperm ducts. Oocytes mature in a caudo-cephalic direction; no oviduct nor female pore is present. The spermatozoa are fusiform, with a very short tail. The anterior end of the sperm is a small, conic hood which corresponds to the acrosome. The following, spindle-shaped corkscrew region contains a nuclear helix surrounding a central axis made of a single, giant mitochondrion. The 9+2 axoneme is enclosed by a bilayered, obliquely striated cylinder only in the proximal tract. The morphology of the reproductive system and spermatozoa of Mesodasys species is discussed, and the hypothesis of hypodermic impregnation in this genus is supported.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002270050652
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