Examples from the Web for planarian
Flat against the stone and not easily perceived may be a chiton, a planarian worm, or a nudibranch.The Sea-beach at Ebb-tide|Augusta Foote Arnold
The planarian worms that I have just been telling about are monsters.
It is now nearly forty years since the presence of chlorophyl in certain species of planarian worms was recognized by Schultze.
These are planarian worms, and though not of prepossessing appearance generally, are extremely interesting animals to study.Country Walks of a Naturalist with His Children|W. Houghton
Instead, much like the planarian cut in halves, it forms a whole animal, half size.