A gonidium (plural gonidia) is an asexual reproductive cell or group of cells, especially in algae. ...
• (n.) A special groove or furrow at one or both angles of the mouth of many Anthozoa. • (n.) A component cell of the yellowish green layer in certain lichens.
Go·nid'i·um noun [ New Latin , from Greek ..., dim. of ... angle.] (Zool.) A special groove or furrow at one or both angles of the mouth of many Anthozoa. 
A gonidium is a special groove or furrow at one or both angles of the mouth of many Anthozoa.