13 ACTA ZOOLOGICA BULGARICA Acta zool. bulg., 62 (1), 2010: 13-20 Introduction Over the last few decades there has been a grow- ing interest in using testate amoebae in applied ecol- ogy, e.g. as bioindicators to monitor a wide range of environmental changes, from global warming to pollution hazards. This polyphyletic group of pro- tists is also used as good model for palaeoecological, biogeographical and evolutionary studies (Berger et al. 1986; Tolonen 1986; Foissner 1994, 1997, 1999; Nguyen-Viet et al. 2004; Mitchell et al. 2008, etc.). Unfortunately, the existence of many poorly de- scribed species and a high number of synonyms in the group are sometimes a serious problem for the performing of reliable studies. That is why it is nec- essary to study these species in detail, using modern methods (scanning electron microscopy and molec- ular-genetic methods), and to revise their taxonomi- cal status. During our investigation on the nebelids from Bulgaria, we observed an abundant material of Nebela that corresponded to Difflugia nebeloides. This provided the opportunity to study the shell ul- tramorphology and the morphometric variability, as well as to define more precisely the taxonomical sta- tus of this rare and until now poorly described spe- cies. For comparison we have studied also material from Austria. Material and Methods The specimens for the present study were isolated from wet Sphagnum mosses gathered at minero- trophic Sphagnum swamps, situated at ‘Platoto’ (42°36΄N lat., 23°17΄E long.; 1850 m a.s.l.) in Vitosha Mountain (Bulgaria) in August 2009 and Is Difflugia nebeloides (Amoebozoa: Arcellinida) Really a Difflugia? Re-description and New Combination Milcho Todorov 1 , Vassil Golemansky 1 and Ralf Meisterfeld 2 1 Institute of Zoology, Bulgarian Academy of Sciences, Sofia, Bulgaria; E-mails: mtodorov@zoology.bas.bg, golemansky@zoology.bas.bg 2 Institute for Biology II, RWTH Aachen University, D-52056 Aachen, Germany; E-mail: meisterfeld@rwth-aachen.de Abstract: Sphagnum dwelling Arcellinida is the best studied group of testate amoebae. Nevertheless there are many rare and poorly documented species that are not easily identified and therefore often overlooked. Here we re-describe a species that initially had been described by GAUTHIER-LIÈVRE & THOMAS (1958) as Difflugia nebeloides. Detailed light- and scanning electron microscopic investigations on the shell ultrastructure and biometric analysis of the morphometric variability of this species were performed. The results clearly show that the shell in this species is composed of a mixture of oval, circular and quadrangular siliceous shell plates collected or predated from other Arellinida or Euglyphida. It has the typical test structure of the genus Nebela. Based on these results, the following systematic change is proposed: Nebela nebeloides comb. nov. (Syn.: Difflugia nebeloides GAUTHIER-LIÈVRE & THOMAS, 1958). Key words: Testate amoebae, Amoebozoa, Arcellinida, Difflugia nebeloides, Nebela nebeloides comb. nov., biometry, morphology