ectocyst (ektosist)

[ As a rule the colonies [of polyzoans] po e a horny or parchment-like, frequently also calcareous, exoskeleton, which arises from the hardening of the cuticle around the individual zooids. Each zooid is accordingly surrounded by a very regular and symmetrical case - the ectocyst or cell; through the opening of which the anterior part of the soft body of the contained zoöid with its tentacular crown can be protruded. Claus, Zoology (trans.), II. 71.