Evolution des Parasitismus am Beispiel rhabdocoeler Plathelminthen (English shop)

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Using morphological data obtained specifically for this study as well as morphological and molecular data taken from the literature, an analysis of modifications towards a symbiotic mode of life was carried out. For this purpose, individual structures such as the epidermis, the digestive and nervous systems, the excretory organs and the gonads were examined in particular. As Tyler & Tyler (1997) established for the epidermis, the symbiotic Rhabdocoela show few to no structural adaptations to their particular mode of life. Thus, phagocytotic food uptake via the epidermis can be discerned in only a few of them. Likewise, the adhesive structures to be expected in ectosymbiotic turbellarians cannot be demonstrated. In the physiology, above all of the digestive apparatus, some species show tendencies towards an adaptation to their habitat. However, there is no particular character that distinguishes a symbiont or even a parasite. In many respects, the symbiotic turbellarians resemble their free-living relatives. Comparison with the Neodermata suggests that there are modifications in the protonephridia and in the structure of the spermatozoa. The data do not appear to be free of contradictions across the various taxa of the Turbellaria. This circumstance also creates difficulties in the search for the sister group of the Neodermata. It is probable that a representative of the taxon Rhabdocoela constitutes the ancestral species or sister group of the Neodermata.