Carolinea 77

176 Carolinea 77 (2019) physis absent. It differs from these three spe- cies in its shorter setae d and l’ on genu IV. The longest of the three setae of this segment of B . daghestanica illustrated by B ulanova -Z achvatkina (1962, p. 207, fig. 2, 1) measures only about 1,4x the segment length. It is not quite clear in this drawing which seta is d and which is l’, though. Belba daghestanica requires redescription. W alter et al. (2014) describe two formally un- named Canadian damaeid species, which they classify under Belba . Their “ Belba species A DEW”, informally named D ave ´ s Hobbit Mite, is readily identifiable by the combination of traits: sensillus clubbed, distally with dense, elongate barbs, plumose; interlamellar setae and leg se- tae strongly plumose; spinae adnatae absent; ventral body length 440 µm ( W alter et al. 2014: p.164, 166). Their second species, “ Belba spe­ cies B DEW”, called D ave ´ s Hairy Hobbit Mite is characterized by: interlamellar setae, pseudanal setae and leg setae coarsely plumose; spinae adnatae present; propodolateral apophysis ab- sent; notogastral setae long (80 µm), smooth with black sheaths; prodorsal tubercles Ba ab- sent, based on W alter et al. (2014: p.167, 168). This species is classified in the present publica- tion under Belbodamaeus and differs in the com- bination of the characters here mentioned from all members of this genus listed in the recent key presented by E rmilov et al. (2013). 3.6 Ecology of Belba sculpta The site where Belba sculpta was encountered in Germany is situated in the Upper Rhine Rift Val- ley, a narrow strip of land, averaging about 40 km in width and being 300 km in length which stret- ches from Basel in Switzerland in the South to Frankfurt in the North. This low-lying region is the warmest in Germany, with the hottest summers, mildest winters and low to moderate amounts of rainfall ( H olzhauer 2013). Mannheim itself is si- tuated at an altitude of merely 95-110 m above sea level and is to a considerable extent shielded from cold weather and rain approaching from the East by the Odenwald Mountains. The Palatinate Forest similarly partially blocks off the effect of the vagaries of weather advancing towards the city from the West. Both mountain ranges formed as horsts during the rifting process which was in- itiated by subsidence in the Eocene about 50 mil- lion years ago, with the Dossenwald site being lo- cated in the graben itself. Accordingly, Mannheim is ranked as having a temperate oceanic climate (type Cfb) in the Köppen climate classification. The daily mean temperature in Mannheim is 11,3 °C, while the average annual high tempe- rature is 16,1 °C. Summers in Mannheim are hot, with an average of 87,6 days per year with temperatures above 25 °C, of which 20 days are classified as tropical with a maximum tempera- ture of 30 °C or more. Winters in Mannheim are very mild with only about 8 frost days annually. Mannheim experiences 1722 hours of sunshine per year and the rainfall in the city and its sur- rounds is very sparse even for the Oberrhein- graben, with an average yearly precipitation of merely 650 mm. The climate statistics presented here derive from the annual values recorded by the Deutscher Wetterdienst during the past 25 years for the measuring station Mannheim Vo- gelstang (DWD 2019). The Belba sculpta specimens from Mannheim were only found in sandy soil with a sparse ve- getation cover of predominantly drought-tolerant moss and lichen. The sand in the Dossenwald is associated with dry grassland habitats and with continental dunes. Twenty large dune fields exist in the area, several of which have been over- grown with forest ( F ischer et al. 2009). The continental dunes of the Dossenwald arose during the Younger Dryas stage ( L öscher 1994) at the end of the Würm glaciation about 11700- 12900 years ago. During this comparatively short timespan of reglaciation within a general period of deglaciation, the Rhine river carried only very little water, and therefore sediments which had been deposited earlier on the floodplain lay ex- posed. A tundra flora and fauna and steppe ele- ments had invaded the Dossenwald region dur­ ing the cold periglacial conditions of the Younger Dryas. This made it possible for the wind to pick up sand particles on a large scale and to deposit them on the lower fluvial terrace of the Rhine at distances up to 3 km away ( F ischer et al. 2009). The formation of aeolian dune deposits mostly stopped with a return to warmer conditions in the Holocene when the Rhine water flow returned to a normal level and reforestation commenced. Sand possesses a negligible water retention capacity and a high evaporation rate. It is also poorly equipped with nutrients since significant organic remains and humus are absent as a rule. The plant growth on sand is therefore general- ly severely restricted and frequently patchy. The lack of a closed plant cover then exposes the sandy surface even more to climatic extremes. The surface temperatures of the sandy soil of the Dossenwald may exceed 70 °C in the summer