USE OF QUANTITATIVE MORPHOLOGICAL ANALYSISCOMBINED WITH A LARGE SAMPLE SIZE FOR ESTIMATINGMORPHOLOGICAL VARIABILITY IN A CASE STUDY OF ARMOURED MITE Carabodes subarcticus Trägårdh, 1902 (Acari: Oribatida: Carabodidae)

The morphology of Oribatida and similar little-known groups of organisms varies considerably, which complicates morphological analysis (e.g. species descriptions). Qualitative analyses have been carried out mostly on a small number of individuals (n 25). There is lack of studies dealing with mechanisms of how that variation can change in relation to sample size and insufficient discussion on whether qualitative or quantitative analysis is more appropriate for description of morphological variability. A total of 500 adult Carabodes subarcticus Trägårdh, 1902 Oribatida were collected from a local population. Six qualitative and six quantitative traits were characterised using light microscopy and scanning electron microscopy. The relationships between the sample size of different subsamples (n 500) and morphological variation were examined using randomised selection (10 000 replicates) and calculation of the percentage of cases in which the sizevalues were within a certain distance (less than 10%, 25%, or 50%) from the range of the reference population (n = 500). Qualitative traits were significantly less variable than quantitative due to binomial distribution of the obtained data; thus they were less comparable and interpretive to describe morphological variability. When sample size was small (n 25), in less than 2 to 15% of cases the observed variability was within 10% distance of the range of the reference population. Larger sample sizes resulted in size-ranges that approached those of the reference population. It is possible that execution of quantitative characterisation and use of relatively larger sample sizes could improve species descriptions by characterising the morphological variability more precisely and objectively.