||Het`e*ro*ne*re"is (?), n. [NL. See Hetero-, and Nereis.] (Zoöl.) A free- swimming, dimorphic, sexual form of certain species of Nereis.

&fist; In this state the head and its appendages are changed in form, the eyes become very large; more or less of the parapodia are highly modified by the development of finlike lobes, and branchial lamellæ, and their setæ become longer and bladelike.