Heteronereis
Heteronereis , noun
[New Latin See Hetero-, and Nereis.]
(Zoology) 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 lamella, and their seta become longer and bladelike.