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(2019)
Serial texts must repeat, so that they can be recognized, but they must also change, so that they can remain interesting. Unusual temporal manipulations can emerge in such texts in order to balance these contradictory demands. This essay studies two serial texts whose need for self-extension produces a suspension of historical time: the contemporary animated sitcom "The Simpsons", and medieval romance as theorized by the twelfth-century poet Wace. I suggest that we might name this temporal constraint fiction.
Background: Approximately 90% of German surface waters do not meet the objectives of the European Water Framework Directive (EU-WFD). This is primarily due to deficits in water body structure and biological quality components, which in turn are negatively affected by chemical pollution. In this context, hydromorphological restoration measures have often been conducted to improve habitat and species diversity and, therefore, the ecological status of water bodies. However, habitat improvement is not necessarily accompanied by biota enhancement and thus by the improvement of the ecological status of rivers. To prioritize water management measures, decision criteria for the water management practice are necessary, which enable the prognosis, whether chemical pollution and its resulting effects or other factors, such as structural deficits of the water bodies, are the main cause for the failure to meet the objective of a good ecological status.
Results: To address this need, we applied the freshwater mudsnail Potamopyrgus antipodarum and the amphipod Gammarus fossarum in active monitoring campaigns and in laboratory experiments with combined water/sediment samples and analyzed water and sediment samples with in vitro assays quarterly over the course of 1 year to provide evidence and guideline to assess if chemical contamination is a relevant stress factor for the aquatic biodiversity in rivers of the Nidda catchment (Hessen, Germany). On the basis of these results, an ecotoxicological, WFD–compliant assessment system was developed which, in comparison with the ecological status classes of the EU-WFD, permits the identification of the probable causes for the failure to meet the objectives of the EU-WFD. From these findings, recommendations for action were derived for the implementation of priority measures in water management practice. For the rivers Nidda, Usa, and Horloff, we identified a need for action to improve water and sediment quality at all investigated sampling sites except for the reference sites in the headwaters. The ecotoxicological assessment system also highlighted that hydromorphological restoration measures on their own will not lead to a good ecological status of rivers, as long as water and sediment quality are deficient.
Conclusion: Hydromorphological restoration measures should be performed in conjunction with measures to reduce chemical contamination to achieve a good ecological status of the rivers Nidda, Usa, and Horloff.
European pea crabs - taxonomy, morphology, and host-ecology (Crustacea: Brachyura: Pinnotheridae)
(2010)
Pinnotherids are small crabs symbiotic to a variety of invertebrates. The European species infest bivalves and sea squirts. Their way of life is parasitic and poses a threat to commercially exploited bivalves. While juveniles of both sexes still look very similar - being agile swimmers and partially free living - a metamorphosis takes place in the female after mating and results in a conspicuous sexual dimorphism. Thereafter, the female settles in its host definitely and is morphologically strongly adapted to the parasitic life phase. A very high reproductive output was demonstrated among several pea crab species infesting bivalves. Despite from that, hardly any information is present in the literature on the pinnotherids’ reproductive biology and the underlying morphology.
Due to their cryptic way of life, the sexual dimorphism, and the different morphotypes of the female, the taxonomy of the Pinnotheridae is a serious challenge. Two widely accepted species are recognized on European coasts: Pinnotheres pisum and Nepinnotheres pinnotheres. Pinnotheres pectunculi was so far only known from the bivalve Glycymeris glycymeris in its type locality Roscoff (France), while Pinnotheres ascidicola and Pinnotheres marioni were described as living exclusively in ascidians without careful comparison with the previously described species. In order to produce standardized comparative descriptions, pea crabs were collected and studied from different hosts and localities in the Northeast Atlantic and in the Mediterranean. Nepinnotheres pinnotheres and Pinnotheres pisum were redescribed with consideration to characters of female and male. According to our morphological analysis, Pinnotheres ascidicola and Pinnotheres marioni are junior synonyms of Nepinnotheres pinnotheres, whereas the status of Pinnotheres pectunculi as a valid species was ascertained. Important characters are the mouthparts, the male gonopods, and especially chelipeds that showed consistent characteristics among different crab stages of both sexes.
Based on our sampling, we estimated the host-range of the European species. Nepinnotheres pinnotheres lives in ascidians and in the pen shell Pinna nobilis. Pinnotheres pisum infests numerous bivalve species - Pinna nobilis included. For Pinnotheres pectunculi novel host records are presented, all from the bivalve family Veneridae. Furthermore, feeding of the Pinnotheres-species was observed. They use a setae comb ventrally on the claw to brush mucus (and the accumulated food particles) from the bivalve gills. Feeding strategies and host-ecology will be thoroughly discussed in consideration to other Pinnotheridae.
We investigated the reproductive systems of European pinnotherids by histological methods, scanning and transmission electron microscopy, and confocal laser scanning microscopy.
The Eubrachyura have internal fertilization: paired vaginas enlarge into storage structures, the spermathecae, which are connected to the ovaries by oviducts. Sperm is stored until the oocytes are mature and transported into the spermathecae, where fertilization takes place. In the investigated pinnotherids, the vagina is of the ‘concave pattern’. Musculature is attached alongside flexible parts of the vagina-wall to control the dimension of its lumen. The genital opening is closed by a muscular mobile operculum.
The spermatheca can be divided into two distinct regions by function and morphology. The ventral part includes the connection with vagina and oviduct and is regarded as the zone where fertilization takes place. It is lined with cuticle except where the oviduct enters the spermatheca by the ‘holocrine transfer tissue’. At ovulation, the oocytes have to pass through this multi-layered glandular epithelium, which has a holocrine mode secretion. The dorsal part of the spermatheca is lined by a highly secretory apocrine glandular epithelium, which was to date only found in fiddler crabs of the genus Uca.
The male internal reproductive system consists of paired testes and corresponding vasa deferentia. The sperm morphology of pinnotherids conforms to other thoracotremes, with slight differences between Nepinnotheres pinnotheres and Pinnotheres pisum. Spermatozoa become enveloped into spermatophores in the secretory proximal vas deferens. The medial vas deferens is strongly enlarged and stores spermatophores embedded in seminal plasma. The distal vas deferens holds tubular appendices, which extend into the ventral cephalothorax and slightly into the pleon. These appendices produce and store vast quantities of seminal plasma. The copulatory system of the Brachyura is formed by paired penes and two pairs of gonopods, which function in sperm transfer. In pinnotherids, the long first gonopods transfers the sperm mass to the female. It holds the ejaculatory canal inside, which opens proximally and distally. The second gonopod is solid, short and conical. During copulation, the penis and the second gonopod are inserted into the base of the tubular first gonopod. The second gonopod functions in the transport of the sperm mass inside the ejaculatory canal towards its distal opening. The specific shape of the second gonopod is strongly adapted for a sealing of the tubular first gonopod with longitudinal cuticle foldings that interlock inside the first gonopod. The presented results are discussed concerning their function in reproduction and in respect of the systematic account.
The role of secretion in sperm transfer, storage and fertilization among the Brachyura is still under debate. It is notable that structure and function of secretion are more complex in pinnotherids and probably more efficient than in other brachyuran crabs, which will be discussed, in view of the parasitic way of life and the high fecundity of pinnotherids.