Cytology and Cytogenetics

  • Roberto BertolaniEmail author
  • Lorena Rebecchi
Part of the Zoological Monographs book series (ZM, volume 2)


Several cytological aspects have been considered in tardigrades. Firstly, the cell constancy which is not a true eutely being several mitoses present even after hatching, even though some organs, such epidermis and nervous ganglia, have the same cell number in juveniles and adults. The total number of these cells is species-specific. Then the ultrastructure of cuticle, epidermis, feeding and digestive apparatus, excretory and osmoregulatory organs, muscles, nerve cells, sensory cells and storage cells has been considered. Instead, the ultrastructure of the germ cells has been considered in the chapter on reproduction. With regard to chromosome number and shape, it has been observed that generally there is little difference among the species (n = 5 or n = 6), but several cases of polyploid populations exist, often very similar to diploid populations from a morphological point of view. In most cases the polyploid populations do not have males and reproduce by apomixis. Studies on the genome size have confirmed the presence of polyploid populations, as well as the presence of nuclei with multiple amounts of DNA within the same specimen. The genome size of the tardigrades is always relatively small and does not seem related to phylogenetic lineages. Studies on tardigrade genomes have placed this phylum at the centre of discussions on the evolution of Metazoa and have considered the role of horizontal gene transfer in animal evolution with contrasting results.


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© Springer Nature Switzerland AG 2018

Authors and Affiliations

  1. 1.Department of Education and HumanitiesUniversity of Modena and Reggio EmiliaModenaItaly
  2. 2.Civic Museum of Natural HistoryVeronaItaly
  3. 3.Department of Life SciencesUniversity of Modena and Reggio EmiliaModenaItaly

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