FIRST FINDINGS OF THE CLAM SHRIMPS LEPTESTHERIA SARS , 1896 AND IMNADIA HERTZOG , 1935 ( CRUSTACEA , CONCHOSTRACA ) IN THE WESTERN FOOTHILLS OF THE STARA PLANINA MOUNTAINS

During 2004 conchostracans Imnadia and Leptestheria were recorded near the Serbian-Bulgarian border, in the foothills of the Western Stara Planina Mountains. Leptestheria occurred in relatively large density and was presented by adults of both sexes. Imnadia was identified only by resting eggs separated from the pond sediment. This is the first report of genus Imnadia in the Balkans, and also a first record of the second genus in the limnological area of the ‘Eastern Balkans’.


INTRODUCTION
Clam shrimps, wich belong to the conchostracan group of large branchiopods (Branchiopoda, Crustacea), need a dry period for egg hatching and are progressively eliminated at higher latitudes, where low temperatures slow embryonic development and the growth rate (Brtek and Thiéry, 1995).Belk(1977) and Geddes (1983) showed that species richness is related to habitat diversity.In regions with alternation of dry and rainy periods, species richness increases from the extremely dry southern regions, to the northern ones with rainy climates.

General distribution pattern
The genus Leptestheria Sars, 1896 has a worldwide distribution (North America, Europe, Asia, and Africa).The geographic distribution of the genus in Europe is shown in Fig. 1.Leptestheria mainly inhabits the Pannonian lowlands and the Romanian or Wallachian plains in the basins of the lower Danube and lower Dniester Rivers in continuation with the Ukrainian steppes (Bânârescu, 1991).The genus also inhabits some places in the 'Eastern Balkans' and 'Dinaric Western Balkans' (according to Illies, 1978).
Imnadia Hertzog, 1935 is an endemic European genus.It is present in Central Europe (Fig. 2), mainly on the Pannonian Plain (lowlands in Austria, Slovakia, Hungary and Northern Serbia) and in the lowlands of Romania (in the basin of the Middle Danube).Until now there were no data indicating the presence of this genus in the Balkans (Bânârescu, 1991;Brtekand Thiery, 1995).

Distribution in Serbia
To date investigations of Conchostraca in Serbia were performed mainly in the northern parts (on the Pannonian Plain), whereas data from the southern region of the country were scarce (Marinček and Petrov, 1991).
Within the genus Imnadia three species have been found in Serbia: I. cristata Marinček, 1972, I. banatica Marinček & Valvajter, 1982, and I. panonica Marinček & Petrov, 1984, all in the Pannonian part of the country.On the IUCN Red List of Endangered Species, they are listed as vulnerable (Sket, 1996).

MATERIAL AND METHODS
This research is based on our field investigations during 2004 near the Serbian-Bulgarian border, in the western foothills of the Stara Planina Mountains.The investigated area is situated along the left bank of the Nišava River 4 km upstream from the city of Pirot near the village of Trnjana (43 o 07.403' N and 22 o 40.148'E) at an altitude of 387 m.Specimens were collected from shallow pools on an unpaved road.Sampling was carried out using standard technique (specimens were collected with a hand net and preserved in ethanol).Both resting eggs and carapaces were dehydrated in alcohol, mounted on stubs, coated with gold (10 nm at 25 kV, Bal-Tec SCD 005), and observed under a JEOL JSM 6460LV scanning electron microscope.Diameter was measured with the SEM numerical point-point system.

RESULTS AND DISCUSSION
Leptestheria (family Leptestheriidae Daday, 1923) occurred in relatively large numbers.Females were somewhat smaller than males.Up to 10 growth lines were present.To judge from diameter of the carapace and the number of growth lines (Petrov, 1990;Petrov and Marinček, 1995), they were younger adults.Generally, setae were present along the free margin of the shell and (particularly in females) along the growth lines, as in L. saetosa (Fig. 3).Females had trunk limbs modified to structures that glue eggs to the abdomen, but we did not observe any clutch of resting eggs within the carapace in the present population.
We identified the genus Imnadia (family Imnadiidae Botnauric & Orghidan, 1941) only on the basis of resting eggs separated from the pool sediment.In this genus the cyst patterns are unique among large branchiopods and can be considered as generic (Thiéryet al., 1995).Eggs are ovoid, 175 to 179 μm in size, with characteristic spiraled surface (Fig. 4).

Ecology
Leptestheria was found in late spring.Specimens occurred in high density in the same pool with Imnadia eggs.The pools were small, turbid and shallow, with a muddy bottom.They co-occurred with Branchipus Schaeffer, 1766 and gastropods.Their potential predators (frogs) were also present.pH of the water varied between 7 and 8.The water temperature was 21°C.

Distribution pattern
The genus Leptestheria is known mainly from the lowland regions and river valleys of Europe (Brtek and Thiéry, 1995).Thus, the record of this genus along the  Nišava River in Eastern Serbia was to some extent expected.This population probably belongs to L. saetosa, to judge from the presence and distribution of setae on the shell (Marinček and Petrov, 1992).
Up to now there were no confirmations of the presence of the European endemic genus Imnadia in the limnological area of the Balkans (according to Illies, 1978).
Both Imnadia and Leptestheria were previously noted mainly in the northern parts of Serbia (Fig. 5) and were determined as faunal elements of the Pannonian region (Petrovand Petrov, 1997).The evidence from the western foothills of the Stara Planina Mountains represents the first findings of the given genera in this region.Brtekand Thiéry(1995) noted mountainous regions of the Balkans as climatic refugia during periods of glaciation, aridization, and transgressions and as a center of diversification of some branchiopod families in Europe, including Limnadiidae Burmeister, 1843 [Brtek and Thiéry(1995) consider the genus Imnadia to be a member of the family Limnadiidae].According to the same authors, Imnadia is distributed between 40 o N and 50 o N. Thus, finding of Imnadia in the investigated area was to be expected and additionally supports Brtek and Thiéry΄s theory.One of the possible paths of dispersal of these genera could be through the northward corridor composed of the Morava and Danube Rivers.Another possibility is that the Pannonian Plain, which is noted as a distinct area of endemism in Central Europe (Bânârescu, 1991), could be the center of origin of these genera, Leptestheria in particular.
Our finding represents the first report indicating the presence of the genus Imnadia in the Balkans.The presence of Imnadia and Leptestheria in the western foothills of the Stara Planina Mountains further suggests the possibility that the given genera can also be found in other parts of these mountains.Marinček andPetrov, 1991 andPetrov andPetrov, 1997, combined).The region of new findings of these genera is marked with a triangle.Conchostraca (Crustacea: Branchiopoda) in Yugoslavia.Hydrobiologia 359, 29 -35. Sket, B. (1996).Imnadia banatica, Imnadia cristata, Imnadia panonica.