Abstract 117
Pavlíček, T., Hadid Y., Cohen T., Glasstetter M., Snir S., Mısırlıoğlu M., Pearlson O., Yadav Sh., Csuzdi Cs. and Král P. 2014: “Opening Pandora’s Box”: II. Segmentation and evolution of hermaphroditic annelids. Advances in Earthworm Taxonomy VI (Annelida: Oligochaeta) Proceedings of the 6th International Oligochaeta Taxonomy Meeting (6th IOTM), Palmeira de Faro, Portugal, April 22-25, 2013. Zoology in the Middle East, 2014: 038–049, Kasparek Verlag, Heidelberg.
The conspicuous but relatively simple bilateral body organization in hermaproditic annelids could be ideal for the modelling of molecular/organismal relationships. This is however not the case. Our results support the hybrid (A and B) origin of hermaphroditic annelids, which technically are hybrid chimeras, and explain the tail origin in Oligochaeta. Since the prostomium and pygidium differ from the majority of the body segments, taxonomists often regard them as asegmental structures and do not count them among segments. Our results indicate that the predecessors’ prostomia, which lost their dominant anterior position during hybrid polyploidizations, are associated with the appearance of female organs (such as ovaries), the presence of a budding zone in Polychaeta and the pygidium in Oligochaeta. We believe that the distribution pattern of the current and former prostomia along the anterio-posterior body axis is of great significance for the regeneration of segments. Historically, the first hybrid polyploidization events possibly brought together the male-like and the female-like predecessors. The number of body segments could have been determined by control elements perhaps associated with a centrosome. By this or other means, the paratomic fission combined with pygidial budding can lead to the occurrence of specimens with different numbers of segments in panmictic populations in both Polychaeta and Oligochaeta. This could be seen, for example, in Aeolosoma hemprichi, which possesses seven or eight segments (the most anterior prostomium is not counted as a segment following the traditional approach in earthworm taxonomy). Since our results show that the annelid body segmentation might represent a centrosome-built structure, we searched for a latent segmentation (corresponding to cilia in the genesis of which the centrosome is playing an important role), and indeed, we discovered a notably large number of small units that we named “microsegments”. Our discoveries should be applicable to the taxa with which the studied annelids share the ancestral monoastral spindle, the spiral cleavage of embryo and the common ancestor.

Keywords. Annelida, hermaphroditism, segmentation, paratomic fission, microsegments, latent segmentation.

 

 

 

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