Acta Protozool. (2002) 41: 239 - 244 Morphology, Biometry and Ecology of Nebela bigibbosa Penard, 1890 (Protozoa: Rhizopoda) Milcho TODOROV Institute of Zoology, Bulgarian Academy of Sciences, Sofia, Bulgaria Summary. Testate amoeba Nebela bigibbosa Penard, 1890, isolated from the litter of beech forests in Bulgaria and its morphology, biometry and ecology have been investigated. Size frequency distribution analysis indicates that N. bigibbosa is a size-monomorphic species, characterized by a main-size class and a small size range (95% of all measured individuals have a shell length 145-170 µm and 92% have a shell width 94-110 µm). The investigations of the ecology of N. bigibbosa show that it is not a typical inhabitant of Sphagnum mosses, but is closely related and frequently found in the litter of deciduous forests (mainly beech forests) and can be used as an indicator for these biotopes. Key words: biometry, ecology, morphology, Nebela bigibbosa, Rhizopoda, Testacea. INTRODUCTION The genus Nebela is one of the well-studied genera of the testaceans. It includes comparatively large spe- cies, which in most cases are clearly differentiated and well distinguished each other. More than 120 taxa of the genus Nebela have been described until now. Most of them live in mosses and litter, and rarely occur in other biotopes (soils, littoral, pelagial and benthal of the fresh- water pools, etc.). Nebela bigibbosa is one of the largest and well- distinguished species of the genus Nebela. It is charac- terized by the presence of two large pores on the broad lateral face of the shell. The species was described by Penard (1890) in mosses from the environs of Wiesbaden (Germany). Although the studies of the freshwater and Sphagnum-dwelling testaceans were exceptionally in- tensive in the beginning of 20th century, this species has been reported only from Germany, Ireland, Great Britain, Spitsbergen, Canada and Java till 1960 (Penard 1890, 1903, 1905; Wailes and Penard 1911; Cash et al. 1919; Deflandre 1936; Hoogenraad and de Groot 1940; Jung 1942). The fact that the majority of the above authors have rarely found N. bigibbosa as single individuals might be the reason of the lack of more biometrical and ecological data about this species. The aim of the present study is to characterise morphologically, biometrically and ecologically N. bigibbosa using abun- dant material, isolated from the litter of beech forests in Bulgaria. Address for correspondence: Milcho Todorov, Institute of Zoology, Tsar Osvoboditel Blvd. 1, 1000 Sofia, Bulgaria; Fax: (3592) 988-28-97; E-mail: zoology@bulinfo.net