\Spo"ro*sac\, n. [Spore + sac.] (Zo["o]l.)
(a) A hydrozoan reproductive zooid or gonophore which does
    not become medusoid in form or structure. See Illust.
    under {Athecata}.
(b) An early or simple larval stage of trematode worms and
    some other invertebrates, which is capable or reproducing
    other germs by asexual generation; a nurse; a redia.