A NEW RECORD OF HAPLOTAXIS GORDIOIDES ( HARTMANN , 1821 ) ( OLIGOCHAETA , ANNELIDA ) IN THE BENTHOCENOSES OF A POTAMON-TYPE RIVER ( SAVA RIVER , SERBIAN SECTOR )

The species Haplotaxis gordioides (Hartmann, 1821), from the family Haplotaxidae (Oligochaeta), was found for the first time in a lowland, potamon-type river (Sava River, Serbian sector) in 2002. This new record adds to our knowledge of the range and spreading of the given species. .


INTRODUCTION
Haplotaxid worms are primitive oligochaetes (Brinkhurst, 1984(Brinkhurst, , 1992) ) found primarily in groundwater.The family has a cosmopolitan distribution, but many species are restricted to specific localities or habitats (Brinkhurst, 1978;Brinkhurst and Jamieson, 1971).Also, because the haplotaxids are rarely collected, detailed distribution patterns for most individual species are lacking.Brinkhurst and Jamieson (1971) described the distribution of H. gordioides as Holarctic, and the former author listed several areas of Europe where it has been, or is expected to be found (Brinkhurst, 1978).
Haplotoxis gordioides has not been previously recorded in the oligochaete fauna of the Serbian sector of the Sava River.This Serbian section of the Sava (206 km long) is a typical lowland watercourse located at an altitude lower than 80 m with 0,098‰ declination.The river bed is characterized by a maximal width of close to 1000 m and relatively thick depositions dominated by fractions of fine sand and mud in quiet places.The long-term average water discharge at Sremska Mitrovica is up to 1.500 m 3 s -1 .This paper presents the first records of H. gordioid-es in the oligochete fauna of the Sava River in the Belgrade region, which is the first such finding in this specific type of habitat.

MATERIAL AND METHODS
Our investigations were limited to a 61.5-km-long part of the lower reach of the Sava (Martinović-Vitanović et al., 2004;Paunović, 2004).Sampling was performed in May of 2002 along the right river bank from soft sediment using a Van Veen-type grab with a capacity of of 270 cm 2 .Specimens were found in a habitat with domination of soft bottom substrates (silt, fine sand deposits, and detritus).Animals were separated from sediment with a 200-μm sieve.The samples were fixed with 4% formaldehyde in the field.Sorting and identification were carried out using a binocular magnifier (5 -50 x) and a microscope (10 x 10 and 10 x 40).The preparations of H. gordioides were treated with lactophenol before examination in the laboratory.Taxonomic status was determined according to the guides of Brinkhurst and Jamieson (1971) and Brinkhurst (1988).Specimen photos were made using a digital camera with 6 x magnification.
At the Zabran locality on the Sava River (28.3 km), two partially mature specimens and one immature specimen of H. gordioides (Hartmann, 1821) were ascertained.The observed specimens were consigned to the biological material collection of the Benthological Section, Institute for Biological Research, Belgrade (ref. number 23/2002).Their dimensions were: 1) 63 mm long, diameter 0.5 mm; 2) 52 mm long, diameter 0.5 mm; 3) 40 mm long, diameter 0.3 mm.

RESULTS AND DISCUSSION
According to Šporka (1984), the species H. gordioides was found in cold mountain streams.Schwank`s data (1981Schwank`s data ( , 1982) ) refer to H. gordioides as an interstitial-psammophylic and stenothermic species recorded in mountain springs, streams and head waters in Germany.Later, Šporka (1998) reported the finding of this species in a gravel substratum in the Slovak-Hungarian parts of the Danube River.In Serbia, H. gordioides was previously collected as part of the benthofauna in highland streams only (Simić et al., 1993;Jakovčev, 1996;Kalafatićet al., 1999;Paunovićet al., 2003).Their habitats were characterized by pebbles, sand, and a thin layer of silt with periphyton.The stream benthofauna consisted mostly of insects (Diptera, Ephemeroptera, Trichoptera, Plecoptera).
The finding reported in this paper is the first one in a lowland, potamon-type river (lower sector of the Sava River).Results of quantitative analysis of benthic cenoses recorded at the Zabran locality are shown in Table 1.
At the Zabran locality, H. gordioides was detected only in spring in places where the bottom fauna was characterized by a uniform macrozoobenthic community (H=1.03) with domination of gastropods (66.04%) (Table 1).The investigated sector is directly influenced by urban waste waters from numerous settlements.The saprobic status of the Sava River at the Zabran locality, corresponds to mesosaprobic conditions (β-meso-to α-mesosaprobity) (Table 1).
The record of H. gordioides in the Sava River in the Belgrade region (Zabran) is especially interesting because this species is not characteristic of lowland rivers.
We hope this new record will contribute to a better understanding of the distribution of H. gordioides in Serbia and throughout the Balkan Peninsula.