Folia Historico-Naturalia Musei Matraensis - A Mátra Múzeum Természetrajzi Közleményei 6. (1980)

Domokos, T.: Adatok az Anisus vortex L. faj morfometriájához

I can give the characteristics and the associated species only for biotope 2. Habitat: Lentic water, pH changes cyclically. Eutrophic, reed-grown area with close-set vegetation. Population density: 680/m

3

. 61 pes. A. vortex turned up from a 0.25 m

3 detritus. Associated with species: Valvata cristata О. Г. MÜLLER, Bithynia tentaculata (L.), B. leachi (SHEPPARD), Acroloxus lacustris (L.), Lymnaea palustris f. corvus (О. F. MÜLLER), Physa fontinalis (L.), Planorbarius corneus (L.), Planorbis planorbis (L.), Bathyoinphalus contortus (L.), Segmentina nitida (O. F. MÜLLER), Succinea elegáns RISSO, Oxychilus draparnaudi (BECK), Zonitoides nitidus (O. F. MÜLLER), Euconulus fulvus (O. F. MÜLLER), Perforatella rubiginosa (A. SCHMIDT), Unio tumidus RETZIUS. By dividing the studied material in smaller groups (25 samples), I tried to determine the minimal number of individuals needed to a sampling that is still good, i. e. suitable for further investigations, since the main obstacle in satistical analyses is the small number of individuals available. Measuring was made by means of a magnifying-glass with 0.1 mm scale division. When executing the measurings, it was problematic to choose the origo, marked with О in Fig. 1. (It is on the basis of guessing and eye for proportion, that is why I made unavoidably a permanent measuring-technical mistake.) Besides personal mistakes, one has to reckon also with mistakes issuing from the unequal growth of the shell. The permanent measuring-technical mistake is extenuated by a drawing-out between the measuring-points, even in the case of only one individual. The whole whorls and the half ones spread opposingly. With the growth of the whorl-number the percentage of the mistake decreases gradually up to a stretch, while the extent of the measur ing shows an increasing tendency. Because of the fewer number of the individuals disposing of larger whorls in the population the uncertainty is greaterwith the larger whorls. Fig. 1. a

—b. Parameters of shell: О — origo, R — radius, WN — whorl number, GL — growth lines. Results, conclusions — 1. During the exploratory analyses it was found that a significant deviation could arise during the evaluation according to the logarithmic spiral (Figs. 2, 3). Figure 2 shows clearly the unequal funcion curve that inspires a conception supposing two indépendant sections. The value of т

г is higher than that experienced with A. septemgyratus, and the value of m

2 is 176