Definition of planarian in US English:



  • A free-living flatworm which has a three-branched intestine and a tubular pharynx, typically located halfway down the body.

    Order Tricladida, class Turbellaria: Planaria and other genera

    • ‘Some of these genes have already been found in freshwater planarians, polyclads and acoels, but their expression is still unknown.’
    • ‘In order to prove that the amounts of genomic DNA in planarians and Cladonema were enough for single-copy gene detection under the experimental condition, the Cladonema Pax-B paired box was used to probe the same blot.’
    • ‘The mostly free-living Turbellaria include the planarian, Dugesia, shown above; these are found in the oceans, in fresh water, and in moist terrestrial habitats, and a few are parasitic.’
    • ‘He and his colleagues worked primarily on hydroids and planarians.’
    • ‘In planarian worms, Pax6 orthologs are expressed in developing eyes, but do not appear to be required for eye development.’
    • ‘In planarian regeneration, they could be instrumental to transforming the homogeneous blastema and postblastema fields into discrete patterned regions corresponding to the lost elements.’
    • ‘The neoblast system is best characterized in planarians and macrostomids.’
    • ‘Nevertheless, duplication of Hox genes has been observed, notably in the planarian D. tigrina in which the genes DtGtHoxC and DtGtHoxE were proposed to derive from a recent duplication event.’
    • ‘Thus, we conclude that neoblasts, the totipotent stem cells in the planarians, of acquired sexuals remain ‘asexual’ and the worms require external supply of a sexualizing substance for the differentiation of sexual organs and gametes.’
    • ‘We then conducted competitive hybridization experiments of cDNAs between a head portion and the other body portion of planarians in order to screen genes specifically expressed in a planarian brain.’
    • ‘Here we describe trans-splicing in the freshwater planarian Schmidtea mediterranea, a free-living member of the phylum Platyhelminthes.’
    • ‘To test the function of Hox genes in anteroposterior axis specification in flatworms, single, double and triple injections of dsRNA of Dthox-D and C and GtAbdBb in intact and regenerating planarians are presently being studied.’
    • ‘In Hydrozoans the same orthologous six genes are required for eye regeneration as in planarians, and in the box jellyfish Tripedalia a pax B gene, which may be a precursor of Pax6, was found to be expressed in the eyes.’
    • ‘The expression of Djhox#1053 in X-ray irradiated planarians cut two days after irradiation, was tested by whole mount in situ hybridization.’
    • ‘Irrespective, this evidence establishes the existence of actively crawling organisms, almost certainly bilaterians, and almost certainly above the grade of planarians because of the implied hydrostatic skeleton.’
    • ‘Some animals also show great ability to regenerate: small fragments of animals such as starfish, planarians, and Hydra can give rise to a whole animal.’
    • ‘He received his Ph.D. in 1902 working on the behavior of planarians and stayed on as instructor of zoology until 1906.’
    • ‘Around the same time, they reported that planarians move away from intense visible light, and they showed that even blinded planarians are negatively phototaxic.’
    • ‘The planarians used in these studies, also called flatworms, live in fresh water and have a singular ability to regenerate.’


Mid 19th century: from modern Latin Planaria (feminine of Latin planarius ‘lying flat’) + -ian.