The Collaborative International Dictionary
Sagittocyst
Sagittocyst \Sag"it*to*cyst\, n. [See Sagitta, and Cyst.] (Zo["o]l.) A defensive cell containing a minute rodlike structure which may be expelled. Such cells are found in certain Turbellaria.
Wiktionary
sagittocyst
n. A capsule having a spindle-like needle produced by epidermal cells of certain turbellarians.