Shell Size of the Freshwater Snail Radix auricularia (Linnaeus, 1758) Collected from Water Vegetation: A Case Study from South-East Bulgaria

The specimens of the freshwater snail Radix auricularia collected from Southeastern part of Bulgaria during the cold period as a whole were with mean shell height of 3.7 mm. During spring and summer it was similar, 3.3 mm. The ratio of the size groups was more equally spread during cold seasons rather than in warm ones. The variation index during cold seasons is about seven times higher than in the warm ones (Var = 13.1 and 2.14, respectively). On the five plant species the gastropods had different mean shell heights. For C. demersum it was 3.4 mm (min-max = 1.4-15.8 mm), and for E. canadensis 7.9 mm (min-max = 2.4-14.6 mm), M. spicatum it was 2.8 (min- max = 2.4-3.4 mm), P. natans 3.9 (min-max = 1.1-9.0), P. pusillus 4.8 (min-max = 3.1-8.2).