Taxonomic publications: past and future - Senckenberg Museum

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Burckhardt & Mühlethaler (eds): 8 th GfBS Annual Conference Abstracts 40 Nephridial development in the Onychophora and its bearing on the Articulata hypothesis G. Mayer According to the traditional Articulata hypothesis, segmentation represents the major synapomorphy of the Annelida and Arthropoda. The homology of segmentation indeed seems to be mainly supported by serially arranged coelomic cavities and nephridia only. This support, however, is ambiguous because coelomic cavities are lacking and nephridia are strongly modified in adult arthropods. In view of the recent phylogenetic analyses of molecular data, segmentation of annelids and arthropods must be either convergent or an ancestral feature of bilaterians. In order to clarify the issue, more detailed studies on segmentation in annelids and arthropods are needed. Among arthropods, onychophorans are traditionally considered to share several morphological correspondences with annelids. In order to contribute to the current discussion on the homology of segmentation, I focused on the embryogenesis in the Onychophora. Recent ultrastructural studies on mesoderm differentiation revealed that there are fundamental differences in the formation of nephridia between the Annelida and Onychophora. The metanephridia of annelids originate from single stem cells or “nephridioblasts” whereas the nephridia of onychophorans (and other arthropods) arise from large portions of embryonic coelomic walls. The present and further new findings do not support the traditional Articulata hypothesis, since specific correspondences in organ systems that characterize segmentation in annelids and arthropods are lacking. It remains to be elucidated, however, why serially arranged transitory coelomic cavities arise in arthropods at all. Org. Divers. Evol. 5, Electr. Suppl. 13 (2005)
Burckhardt & Mühlethaler (eds): 8 th GfBS Annual Conference Abstracts 41 The Proscoloplos species complex (Annelida: Orbiniidae) is a single disjunctively distributed species: support from molecular and morphological data Achim Meyer, Harald Hausen, Christoph Bleidorn & Greg Rouse The genus Proscoloplos comprises three species distributed on several locations of the southern hemisphere (South Africa, South America, Australia). Recently Proscoloplos specimens have been identified at the French Atlantic coast as well. According to SEM studies neither the fine structure nor the arrangement of chaetae nor molecular analysis of the ribosomal ITS1 and ITS2 region supports the separation of the three described species and the French population. Intraindividual variability of the repetitive ITS region was tested with up to ten clones per individual. These findings support the inclusion of P. confusus (Hartmann-Schröder, 1962) and P. bondi (Kelaher & Rouse, 2003) in P. cygnochaetus (Day, 1954). The presumed absence of sexual reproduction with larval dispersal in combination with the disjunctive distribution suggests a neozoic origin of the French population. The distribution of branchiae and hooked chaetae are key features in orbiniid taxonomy. Regeneration experiments and comparative analysis between two samples from a single Proscoloplos population, which were exposed to different conditions, indicate environmental effects on the distribution of these characters. The reliability of segmental character distribution for use in orbiniid systematics should be investigated. Org. Divers. Evol. 5, Electr. Suppl. 13 (2005)
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