Flatworm

A planarian, also called a triclad, is a free-living flatworm of the order Tricladida, found in marine, freshwater and terrestrial settings and grouped into three suborders, Maricola, Cavernicola and Continenticola. It is a bilateral flatworm without a body cavity, with a three-branched intestine, and lacks circulatory or respiratory systems, absorbing oxygen through its skin, moving by cilia and muscular contraction, and reproducing sexually, asexually by fission, or both depending on species. Planarians are known for their ability to regenerate missing tissues and organs, a process driven by abundant adult stem cells called neoblasts, which makes them important research models for regeneration, stem cells, aging, toxicology, genetics and memory.