![]() ![]() wilhelma tend to display very regular contraction patterns over periods of hours and days. In a closed experimental system, specimens of T. This broad range of contraction cycle duration can occur in one sponge specimen over a period of a week under natural or natural-like conditions in the aquarium, where many factors influence the sponge (see below). wilhelma contraction has been observed to occur regularly at intervals between 60 and 600 min, with frequencies of 2.8×10 -4 to 2.8 ×10 -5 Hz, respectively. Much more effort is needed on this topic, which is directly linked to basic questions about the evolution of multicellularity,and for which experimental model sponge systems are needed. This polarizing discussion concluded with the statement that sponges do not possess a nervous system, but did not explain the mechanisms underlying coordination in the aneural Porifera. The main foci of these discussions have been whether or not sponges possess a nervous system ( Jones,1962 Lentz, 1968 Mackie, 1979, 1990 Pantin, 1952 Parker, 1910, 1919 Pavans de Ceccatty, 1960 Perovic et al., 1999) and other possible mechanisms of integration( Jones, 1962 Pavans de Ceccatty, 1974, 1979 Weyrer et al., 1999). The integration and coordination of this behaviour has been widely discussed over the last 50 years. Nevertheless, since the time of Aristotle(384-322 BC) it has been well known, at least among sponge scientists, that sponges can contract (see Aristotle,1498 Lieberkühn,1859 Schmidt,1866 Weissenfels,1990), react to external stimuli( Emson, 1966 Leys and Mackie, 1997 McNair, 1923 Pavans de Ceccatty, 1979) and even move ( Bond, 1992 Bond and Harris, 1988 Fishelson, 1981 Jones, 1957 Kilian, 1967 McNair, 1923). Sponges are generally regarded as sedentary organisms with no striking degree of behaviour or irritability. wilhelma as a model organism for research on the development of aneural signal transduction and integration during early Metazoan evolution. The reported results and techniques establish T. If two individuals of a clone are fused, the individual contraction rhythm of both sponges persists for several days, until a single new individual sponge is formed with a synchronized rhythm. The contractions seem to be mediated by the pinacoderm they are triggered locally and spread over the sponge surface at 12.5 μm s -1. Long-term observations (for >7 days) reveal that the sponge contractions display a day-night periodicity in which contraction cycles are significantly longer during the dark hours. Each contraction cycle follows a characteristic pattern of four phases, permitting analysis of the kinetics of contraction and expansion. The sponges are able to reduce their body volume by up to 73.3% during regular contractions. For the first time, differential, quantitative data on sponge behaviour could be obtained. Sponges of the species Tethya wilhelma display rhythmic body contractions, which were analyzed by digital timelapse imaging and semi-automated image analysis.
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