Julita Templin, Lech JacunAski and Teresa Napiórkowska
Metameric Malformations of Opisthosoma in Tegenaria Atrica (Araneae, Agelenidae)
The opisthosoma of Tegenaria atrica is characterized by a high morphological stability, as it is exceptionally resistant to the teratogenic effect of most abiotic factors except temperature. The least frequent opisthosomal anomalies found in our experimental material were disturbances in the colouring of opisthosoma. Another rare anomaly was the elongation of the postspinneret zone of the opisthosoma, resembling the postabdomen of other arachnids. The occurrence of a much narrower elongation, sometimes with traces of segmentation, resembling the postabdomen the advanced spider, can be interpreted as a specific atavism. An equally rare anomaly was the presence of two independent anal orifices in the postspinneret zone. All the above-described anomalies appear extremely rarely, and some of them are related to the atavistic characteristics observed in the spiders' ontogeny.
The aim of the study was to determine changes in potamoplankton structure caused by lakes in the fluvial system of the small River Wel. The river flows through 10 lakes. The study was conducted in 2007 and 2008. The selection of sites enabled the assessment of the impact exerted by hydrological conditions of the river on zooplankton, as well as the determination of the effect of lakes situated within the river course on the analysed assemblage of organisms. In total 95 species were determined with an average abundance 1026 ind. 10 dm-3. Rotifers dominated qualitatively and quantitatively and among crustaceans - Copepods. Lakes seem to be the main source of zooplankton in the fluvial system of the Wel River. The lakes disturb the river continuum, but their impact on the structure of zooplankton is short-lived. Due to the presence of flow-through lakes along the river, species richness of zooplankton in the Wel River is similar to that in large rivers.
Teresa Napiórkowska, Lech Jacuński and Julita Templin
Epimorphosis of Heterosymelic Appendages in Tegenaria Atrica (Araneae, Agelenidae)
Studies of epimorphic regeneration of appendages were carried out on larvae and nymphs of Tegenaria atrica C.L. Koch with heterosymely (accretion of appendages on the same side of the body) of two walking appendages and of walking appendages with pedipalpi. All the anomalies were obtained by exposing developing embryos to alternate temperatures of 14 and 32°C. Amputation of fragments of anomalous appendages was always followed by regeneration. Based on the characteristic external structures of the regenerating joints, successive stages of epimorphosis were estabilished, whose start and end were marked by ecdyses. Several types of regenerates were found, whose anatomical structure did not undergo further significant changes until the end of our observations.
Oligomely is a type of developmental anomaly occurring in embryos of the spider Tegenaria atrica C.L. Koch under the teratogenic influence of temperature. This anomaly is of metameric origin, as it results from a disorder of metamere formation on the germ band during embryogenesis, resulting in the absence of one half or the whole metamere. In such a case, one or more appendages are missing on one or both sides of the body in a spider leaving a chorion. This anomaly induces changes both in the anatomical structure and exoskeleton of a spider (deformation of carapace and sternum). Carapace length and sternum area were measured, as well as the duration of the subsequent nymph stages of oligomelic individuals with one of the walking appendages missing (always on the right side of the body) was recorded. The consecutive nymph stages of oligomelic individuals lasted for a much shorter time compared with control specimens. This acceleration of development is probably to offset losses incurred during embryogenesis. In the early postembryogenesis, oligomelic specimens exhibited shorter carapace length and smaller surface area of the sternum compared to control individuals, which resulted from the lack of half of the metamere corresponding to the missing leg. However, in older nymph stages, a strong tendency for the faster growth of both carapace and sternum was observed, which can be defined as a compensatory growth increase making up for the losses caused by the anomaly.