• (n.) The outer, hardened integument which covers most hydroids.
Per'i·sarc noun [ Prefix peri- + Greek ..., ..., flesh.] (Zoology) The outer, hardened integument which covers most hydroids. 
perisarc 1. The horny or chitinous outer case or covering protecting the soft parts of hydrozoans. 2. The outer, hardened integument which covers most hydroids.