New species Semitobrilus filipjevi sp. n. from Laos and taxonomic structure of the genus Semitobrilus Tsalolikhin, 1981 (Nematoda: Tobrilida, Tobrilidae, Neotobrilinae)

A description of the new species Semitobrilus filipjevi sp. n. from Laos is given. The new species differs from the other species of the genus by its long head setae. The new species differs from S. pellucidus in the length of the head setae (more than 50% of the head width) and the presence of crystalloids in the body cavity. The new species was discovered in the silty-sandy soil from a forest pond in southern Laos. An identification key of the species and a refined diagnosis of the genus Semitobrilus is provided. The species characters and species composition of the genus Semitobrilus are discussed. It is proposed to synonymize the species S. closlongicaudatus (Gagarin, 1971) with the species S. longicaudatus (Hofmaenner, 1913). The species S. gagarini (Ebsary, 1982) is transferred to the category sp. inq. The length of the head setae is the main character of the species. The presence of crystalloids in the body cavity is an unreliable character. Errors in the descriptions of S. ebsaryi, S. gagarini, and S. pellucidus are discussed. The work used the materials from the collection of the Zoological Institute of the Russian Academy of Sciences, including the original slides by I. N. Filipjev.

Substrate choice by the alien snail Ferrissia fragilis (Gastropoda: Planorbidae) in an industrial area: A case study in a forest pond (Southern Poland)

The aims of this study were to determine the substrate choice by the alien snail Ferrissia fragilis (Tryon, 1863) (Phragmites australis and Typha latifolia remains, Nuphar lutea floating leaves and leaf deposit) as well as the environmental factors that influence the occurrence of this species. From 9 (T. latifolia and P. australis) to 11 (leaf deposit) snail species occurred on each type of substrate. F. fragilis belonged to the eudominants on most of the substrate types. This species reached its highest average density on floating N. lutea leaves (271 ind. m−2) and the lowest was on P. australis (60 ind. m−2). It occurred in different periods during the snail collection: in the initial study period on the floating N. lutea leaves (May) and on P. australis in the final period of the study (September). In July, we found a few specimens in the postseptal form on T. latifolia remains. The results of RDA analysis confirm the association between F. fragilis and T. latifolia as well as with floating N. lutea leaves. F. fragilis occurs at sites that have a higher content of calcium and iron in the water. Alien species more increasingly appear in disturbed anthropogenic water-bodies. An important vector in the dispersion of F. fragilis was probably the water birds or the economic activities that are related with the use of this forest pond. Studies on the occurrence of alien species contribute important data on the activities that are taken to preserve the biodiversity of freshwater environments

Ecology of Hydrozetes Berlese, 1902 (Acari, Oribatida) at various water bodies near Bydgoszcz (northern Poland)

Ecology ofHydrozetesBerlese, 1902 (Acari, Oribatida) at various water bodies near Bydgoszcz (northern Poland)Mites of the genusHydrozetesBerlese, 1902 are abundant and important in wet habitats and can be useful in palaeoecological studies and bioindication. However, due to problems with their identification, there is still a limited knowledge on their ecology. In this study, 5Hydrozetesspecies have been investigated. The most abundant wasH. lemnae(about 121 000 ind./m2), which constituted 76% of the total Oribatida at a pond shore in the Botanical Garden in Myślęcinek in Bydgoszcz. Its population density was lower in duckweed and filamentous algae on the water surface of the same pond. This species was found also in several other bodies of water, varying in water quality, but it preferred neutral pH.Hydrozetes thienemannihad a narrower ecological tolerance and was restricted only to a forest pond with neutral pH in Pruszcz, where it dominated among the Oribatida. Three other species -H. lacustris, H. octosetosus, andH. longisetosus- were found only in acid water. The last mentioned species was absent from the peat pond in Bagno Chlebowo Nature Reserve, with a high concentration of sulphur and worse oxygen conditions, but that site was suitable forH. lacustris.