01221nas a2200157   4500008004100000020002200041245003800063210003800101260004400139300001100183520076300194100001800957700001900975700002100994856004801015       2018                        eng d  a978-1-4939-7802-100aPlanarian Diversity and Phylogeny0 aPlanarian Diversity and Phylogeny  aNew York, NYbSpringer New Yorkc2018//  a1 - 563 aHundreds of planarian species exist worldwide, representing a rich phenotypic diversity. This chapter presents an overview of the morphology and anatomy of various taxonomic groups of planarian flatworms, focusing on features enabling recognition and identification of the animals. The most recent view on the phylogenetic relationships of the planarians is presented, together with geographic distribution patterns of major groups of triclads. The chapter concludes with a brief methodological section outlining species identification on basis of anatomical features. In conjunction with the established laboratory model species, the phenotypic diversity of planarians provides rich opportunities for comparative studies, which this chapter aims to inspire.1 aSluys, Ronald1 aRiutort, Marta1 aRink, Jochen, C.  uhttps://doi.org/10.1007/978-1-4939-7802-1_101983nas a2200145   4500008004100000020001400041245005100055210005100106260001100157300001200168490000800180520158000188100002101768856004801789       2012                        eng d  a1432-041X00aStem cell systems and regeneration in planaria0 aStem cell systems and regeneration in planaria  c2012//  a67 - 840 v2233 aPlanarians are members of the Platyhelminthes (flatworms). These animals have evolved a remarkable stem cell system. A single pluripotent adult stem cell type (“neoblast”) gives rise to the entire range of cell types and organs in the planarian body plan, including a brain, digestive-, excretory-, sensory- and reproductive systems. Neoblasts are abundantly present throughout the mesenchyme and divide continuously. The resulting stream of progenitors and turnover of differentiated cells drive the rapid self-renewal of the entire animal within a matter of weeks. Planarians grow and literally de-grow (“shrink”) by the food supply-dependent adjustment of organismal turnover rates, scaling body plan proportions over as much as a 50-fold size range. Their dynamic body architecture further allows astonishing regenerative abilities, including the regeneration of complete and perfectly proportioned animals even from tiny tissue remnants. Planarians as an experimental system, therefore, provide unique opportunities for addressing a spectrum of current problems in stem cell research, including the evolutionary conservation of pluripotency, the dynamic organization of differentiation lineages and the mechanisms underlying organismal stem cell homeostasis. The first part of this review focuses on the molecular biology of neoblasts as pluripotent stem cells. The second part examines the fascinating mechanistic and conceptual challenges posed by a stem cell system that epitomizes a universal design principle of biological systems: the dynamic steady state.1 aRink, Jochen, C.  uhttp://dx.doi.org/10.1007/s00427-012-0426-4