Epitoky
Nereis and Heteronereis
This is a phenomenon seen in several species of marine polychaete worms like Nereis. The sexually immature stage is called an Atoke and the sexually mature stage is called the Epitoke. The phenomenon of changing of the sexually immature Atoke stage into the sexually mature Epitoke stage is called Epitoky.
Nereis is a polychate worm of Phylum Annelida. Heteronereis is the sexual (reproductive) stage of Neries.
Nereis
Image source: https://upload.wikimedia.org/wikipedia/commons/f/f2/Nereis.jpg
Author: Mark Blaxter
Epitoky in Nereis
In Nereis the anterior region of the body of the worm remains sexually immature and is called the Atoke. The posterior region develops gonads and is called the Epitoke.
There are several differences between Nereis and its Heteroneries stage. These are sumarised below
Nereis
|
Heteronereis
|
|
Sexually
immature stage
|
Sexually
mature stage.
|
|
Body
|
Uniform.
Not divided into Atoke and Epitoke regions
|
Body
divided into anterior Atoke and posterior Epitoke region.
|
Habit
|
Lives
in burrows
|
Free
swimming
|
Parapodia
|
Small
|
Large
with foliaceous outgrowths
|
Setae
|
Small,
Pointed
|
Large,
Oar shaped for swimming.
|
Cirri
on setae
|
Small
|
Large,
provide increased surface area for respiration.
|
Alimentary
canal
|
Well
developed
|
In
the posterior region of the body i.e., the epitoke region, the development of
gonads causes the compression of the alimentary canal.
|
Vikas Yadav
Associate Professor and HOD
Department of Zoology
S V College
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