Het`e*ro*ne*re"is (?), n. [NL. See Hetero-, and Nereis.] Zool.
A free-swimming, dimorphic, sexual form of certain species of Nereis.
⇒ 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 lamellae, and their setae become longer and bladelike.
© Webster 1913.