Morphological variability of Nebela collaris s.s. (Arcellinida: Hyalospheniidae) from Krečko Brdo Hill, East Herzegovina

Abstract

Summary. Nebela collaris s.l. is the best studied species complex within the family Hyalospheniidae. This complex includes 11 taxa established on the basis of small differences in shell shape and size. The type species for this complex (N. collaris s.s.) was defined based on only four specimens. Here we present morphological and morphometric data from moss-dwelling population of N. collaris s.s. from Krečko Brdo Hill (East Herzegovina), based on 765 specimens. Shell length ranged from 87 to 115 μm (previously reported 95-115 μm), shell width from 53 to 73 μm (previously 74-81 μm) and aperture width from 21 to 31 μm (previously reported 28-32 μm). In the literature, reported shell length/shell width ratios range from 1.38 to 1.47, however subsequent morphometric analysis yielded values from 1.33 to 1.91. These data show that N. collaris s.s. can be considered to be a very variable pseudocryptic species among testate amoebae. Coefficients of variation were low for all measured characters in the studied population. Minimal variability (4.28%) was observed for shell length, while maximal variability (6.45%) was recorded for aperture width/shell length ratio. Analysis of the size frequency distribution suggests that the studied population of N. collaris s.s. is size-monomorphic.