Source : Webster's Revised Unabridged Dictionary (1913)

Limulus \Lim"u*lus\ (l[i^]m"[-u]*l[u^]s), n.; pl. {Limuli}
   (-l[imac]). [L., dim. of limus sidelong, askance.] (Zo["o]l.)
   The only existing genus of Merostomata. It includes only a
   few species from the East Indies, and one ({Limulus
   polyphemus}) from the Atlantic coast of North America. Called
   also {Molucca crab}, {king crab}, {horseshoe crab}, and
   {horsefoot}.

Source : WordNet®

Limulus polyphemus
     n : large marine arthropod of the Atlantic coast of North
         America having a domed carapace that is shaped like a
         horseshoe and a stiff pointed tail; a living fossil
         related to the wood louse [syn: {horseshoe crab}, {king
         crab}, {Xiphosurus polyphemus}]