An investigation was carried out on the macrobenthos of Montedoglio Reservoir, an artificial lake in central Italy . Seven qualitative and quantitative samplings, performed by drag netting and airlifting at 5 stations, revealed a total of 48 taxa during 1992-94 . The highest density and most frequent terms were Tubificidae, Chironomidae of the genera Procladius, Tanypus, Chironomus and Polypedilium and Chaoboridae . Tubificidae were found mainly at a depth of 7-9 m, Chironomidae at 1-3 m . The modest density and low biological diversity values are probably attributable to the substrate characteristics and a drop in hypolymnic oxygen during thermic stratification . The oxygen stress at the lake bed, which was unexpected given the scarce planktonic productivity, may have been caused by recent impoundment .

The developmental stages of the larvae of Libellula depressa were investigated for three years in permanent freshwater pools in central Italy. Eleven instars (F-0 -F-10) of L. depressa were discriminated by size and scatter plot. Scatter plots were constructed using the following measurements: labium length, head width, metafemur length, forewing-pad length, and total larval body length. Prolarvae instar was derived by Dyar's law. The mean growth rate coefficient values were about 0.77 for isometric parameters and 0.51 for the forewing-pad allometric parameter. L. depressa appeared to be a 'spring species', as defined by Corbet, and the population we studied had a mainly semivoltine life history and, probably, a small proportion of the larvae a univoltine cycle. Eggs showed direct development.

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Morphometric characters of 961 adult caddisflies, belonging to 327 taxa of the Italian Trichopteran fauna were observed and measured. Sexual dimorphism is reflected in the smaller mean size of males, with mean differences in body length of 12.57%. For the order Trichoptera, regressions of the relationships among body dimensions have been used to estimate the value of exponent b and coefficient a of the allometric function y = a * x b , a power function that describes these relationships very well. The lengths (forewing, head-wing, metafemur, and head) versus body length relationships displayed a high degree of isometry among species, with head-wing and forewing having the highest correlation values (especially in males). The results show that most of the variance depends on isometric size variation and not on allometric shape variation among the different species. For adult caddisflies, this demonstrates constancy of the morphological model in the Italian Trichoptera.

In developing a research on the cholinesterase (ChE) evolution in Invertebrata, this enzyme was studied in the unsegmented marine worm Sipunculus nudus. ChE activity was solubilized through three successive steps of extraction. These fractions are noted as low-salt (LSS), detergent (DS) and high-salt soluble (HSS) and represent 2796, 68% and 5 % of total activity, respectively. LSS and DS ChE were purified to homogeneity by affinity chromatography on edrophonium-Sepharose gel. Purification factors of 1700 (LSS) and 1090 (DS) were obtained. The small amount of HSS ChE prevented a similar purification and an extensive characterization. Based on SDSPAGE and densitygradient centrifugation, both LSS and DS enzymes show a M, value of about 130000 and are likely G, globular dimers of a 67000 subunit. Moreover, LSS ChE seems to be an amphiphilic form including a hydrophobic domain, while DS ChE is probably linked to the cell membrane by a phosphatidylinositol anchor. Both LSS and DS enzymes hydrolyze at the highest rate propionylthiocholine. However, they also show a fairly high catalytic efficiency with other thiocholine esters as substrates, thus suggesting a wide and little-specialized conformation of the active site. Based on immunological cross-reactivity trials, LSS and DS ChE from S. nudus show a reduced structural affinity with a molluscan (Murex brunduris) enzyme. HSS ChE, an acetylcholinesterase, is also solubilized by heparin, like typical vertebrate HSS asymmetric enzymes. However, it lacks fastsedimenting forms and an enzyme-anchoring collagenous structure.The cholinesterases (ChE), ubiquitous enzymes in the animal kingdom, are a class of serine hydrolases which catalyze the splitting of choline esters and are classified as acetylcholinesterase (AChE), propionylcholinesterase (PChE) or butyrylcholinesterase (BChE) according to whether they preferentially hydrolyze the acetic, propionic or butyric ester, respectively. ChE have been detected even in protozoans and sponges. However, it is likely that molecular and functional evolution of these enzymes accompanied development and evolution of the nervous system, since ChE mainly occur in nervous tissues and muscles, where they are involved in the Correspondence to V. Talesa, Dipartimento di Medicina sperimentale, Sezione di Biologia cellulare e molecolare, Via del Giochetto, 1-06100 Perugia, Italy Far: +39 75 5853491.