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This 2-3 cm long, thin brown worm with a wide "anchor" or hammer or crescent shaped head was seen in northern Taiwan slowly moving along a damp tile outdoor surface. It moved by contraction/extension and regularly lifted its head appearing to explore its environment, as if to say "where should I go next"?

Comments suggest that this is a land planarian.

Question: Is it possible to confirm that this is a land planarian and to understand what sensory organs it has on its head in order to "look around" and decide where to go next?

enter image description here

enter image description here

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    $\begingroup$ Related: biology.stackexchange.com/q/55054/16866 $\endgroup$ Commented Feb 16, 2021 at 2:03
  • $\begingroup$ @theforestecologist yes, it does indeed look like a land planarian and the hammer-shaped head was my first clue, thanks! (see also here from here) So all that's left now is the part about how it senses its environment. $\endgroup$
    – uhoh
    Commented Feb 16, 2021 at 3:08
  • $\begingroup$ Edited to reinforce that this is not a duplicate because what's still asked here is the part about how it senses the environment $\endgroup$
    – uhoh
    Commented Feb 17, 2021 at 19:33

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Given that "hammerhead worms" are Bipaliinae, I expect you can find your species from this bibliography1. Bipalium or Diversibipalium ruteofulvum and cosmopolitan Bipalium kewense are mentioned, but I did not find images of these species online just now.

A paper about the sense organs of B. kewense (Abdel-Haleem, 2014) mentions many small pigment cup eyespots, as well as papillae and pits that may be chemosensory in nature.


1Kawakatsu et al. 2004 An Annotated Bibliography of Taiwan Land Planarians, with Lists of Linked Papers on This Animal Group

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  • $\begingroup$ Thanks for your answer! The historical bibliography is intriguing, and also provides a historical view to the colonial rule period. $\endgroup$
    – uhoh
    Commented Feb 18, 2021 at 1:08

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