The Collaborative International Dictionary
Heteronereis
Heteronereis \Het`e*ro*ne*re"is\, n. [NL. See Hetero-, and Nereis.] (Zo["o]l.) A free-swimming, dimorphic, sexual form of certain species of Nereis.
Note: 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 lamell[ae], and their set[ae] become longer and bladelike.