Comparison of measurements and number of annuli in Caloosia paradoxa (Nemata : Hemicycliophorinae)

Summary- Statistical analyses were made on sorne data from six samples of Caloosia paradoxa and one sample of Hemicycliophora arenaria for comparing two methods for measuring the dimensions of organs or the distance between landmarks. The two methods are direct measurement in micrometers and count of the number of body annuli along the organs or between the landmarks. Length in micrometer is more correlated with the width of one annulus than with the corresponding number of annuli. Ir is wrong to estimate the number of annuli by dividing a length by the width of one annulus and it is imperative ta count the actual number of annuli when this type of character is needed. It is more accurate to count the number of annuli along the stylet and the oesophagus than to measure these organs, but it is more accurate to measure total body length and distance from labial disc to excretory pore than to count the annuli. The opposite is true when we compare methods that give the less variable results. Measurement of stylet and oesophagus are less variable than the corresponding number of annuli whereas total number of body annuli and number of annuli between labial disc and excretory pore are less variable than the corresponding measurements. For discriminative purposes, the measurements in micrometers do a bener job than the counts of annuli for discriminating between different species while keeping together different samples of the same species. Ir is concluded that measurements are to be preferred for discriminating purposes, but that the complete description of a species should rely on both measurements and countS of annuli. Résumé- Comparaison entre Tnesure et cOTnptage du nOTnbre d'anneaux chez Caloosia paradoxa (NeTnata: HeTnicycliophorinae)- Des analyses statistiques ont été faites sur des données décrivant six échantillons de Caloosia paradoxa e