The Proto-Indo-European word *karkr(o)-
Word *karkr(o)-
Meaning crab

Comments
Mallory J.P. and Adams D. (2006)

Other words that might be of interest
*dʰĝʰu- ‘fish’, *k̂on- ‘shell’, *laks- ‘salmon’, *peisk ‘fish’, *dhĝhuhₓ- ‘fish’, *pik̂sk̂os ‘fish, trout’