Schmidtea mediterranea Sexual

Smed flatworms are bilaterally symmetric, triploblastic animals that possess a wide variety of differentiated cell types and organ systems. Smed are stable diploids that exist as two biotypes: asexual animals that reproduce by fission, and obligate cross-fertilizing hermaphrodites that reproduce sexually (Newmark and Sánchez Alvarado, 2002; Newmark et al., 2008). Smed embryos are direct developers: newborn hatchlings grow and mature into adult worms without an intervening larval stage (Sánchez Alvarado, 2003). At hatching, juveniles are sexually immature but otherwise possess a body plan grossly similar to the adult hermaphrodite (Sánchez Alvarado, 2003; Wang et al., 2007). These flatworms are renowned for their remarkable regenerative potential: following amputation, small tissue fragments from adult worms of either biotype re-form complete, properly patterned individuals within one to two weeks. Regeneration is dependent on neoblasts, an abundant, cycling somatic cell population comprised of pluripotent stem cells and lineage-primed progenitors. All differentiated tissues in adult planaria, including the germline, are maintained and re-made from neoblast progeny.