The Collaborative International Dictionary of English v.0.48:

Ramulus \Ram"u*lus\ (r[a^]m"[-u]*l[u^]s), n.; pl. Ramuli
   (r[a^]m"[-u]*l[imac]). (Zool.)
   A small branch, or branchlet, of corals, hydroids, and
   similar organisms.
   [1913 Webster]