Edaphologia

Two new species of oribatid mites were collected from garden of Nasu's house alias Tsurutomiyashiki of Shiiba Village in Miyazaki Prefecture, South Japan. New species are Eremulus tsurutomiensis sp. nov. and Oribatella nasuorum sp. nov.

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Field surveys of aquatic oligochaetes were conducted in an organic paddy field once per month in Kamakura, central Japan between June 2010 and May 2011, except during winter. We found eight aquatic oligochaete taxa. The species composition agreed with results from other paddy fields and eutrophic lakes in Japan. The oligochaete community was dominated by the tubicifine Limnodrilus hoffmeisteri and the rhyacodriline Branchiura sowerbyi. The tubicifine Embolocephalus yanaguchii was also collected. This species has been most frequently reported from springs and their outlet streams. Total population density and biomass were 2800 m^<-2> and 21.2 g wet wt. m^<-2>, respectively, lower than those in other similar paddy fields in northern Japan and the Philippines. The population dynamics of B. sowerbyi were examined by size distribution. Growth and reproduction continued until September; however, growth was reduced beginning in October. B. sowerbyi overwintered at various development stages, and newly born individuals were found beginning in April. The management practice for this paddy (organic, winter flooding) seemed to disturb aquatic oligochaeta less than does conventional farming (chemical, winter drainage), therefore the population remained stable throughout the year.

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Sampling soil depth and sorting time were examined for effective investigation of earthworm community by hand sorting in agricultural land. Effective sampling soil depth and sorting time were determined by comparing the biomass and the species number which were established in from 10cm to 50cm soil depth, and in full time and time-limited sorting at volcanic and nonvolcanic-ash soil. Compared to 50cm depth sampling, 30cm depth sampling achieved mean recovery of over 90% of the biomass with 8 % decreasing mean species number. 6 minutes of sorting time was enough for extracting over 90% of mean earthworm biomass from a soil sample of 3.125L (25cm × 12.5cm × 10cm). Maximum individual earthworm biomass was decreasing with increasing sorting time. The earthworms which were found from the 3.125L soil samples after four minutes sampling were mainly immature, rotten, or pieces individuals, accounting for 92.6% of the numbers. It is concluded that sampling from 30cm depth and validated time-limited soil sorting is useful and time-saving approach for studies of earthworm community in agricultural land.

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The keys to the genus and species of Isotominae in Japan are explained. The characters, number of ocellus, shape and appendage of claw, development of furca and shape and arrangement of setae (chaetotaxy) are mainly used to identify the genus and the species. Ten genera, 32 species of Isotominae are explained here. Difference between systems utilized in the recent synopses and the system of Yosii (1977) is explained. Some genera or species may be divided into several genera or species, if we introduced modern systems. The information about chaetotaxy recently becomes important for identification of species of Isotomidae, but only few species in Japan were sufficiently described about it.

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