Diversity of mating behavior in Seaslug

In seaslug we can observed two kind of mating behavior :

In Nudibranchia :


All the genital openings, male and female, are found together on the right side of the body in the anterior quarter (a)

This means two animals must be right side to right side for copulation to take place and each animal is then able to insert its penis into its partner at the same time


Mating partners act as both male and female
at the same time


Chromodoris cf geminus

Joruna rubescens

by Eva Fontaine

"La saline" lagoon, less 1m, 8 November 2008, size : 80 to 120 mm

see also "Mating behavior and spawn event : Jorunna rubescens"

They mate "head to head"




Hypselodoris bullocki

by Sophie Darnis

Passe de l'hermitage, 7 January 2007, size : 30-35 mm

They mate "head to head"

In most Cephalaspidea and Anaspidea


The penis is in a pouch (c) on the right side of the head, quite separate from the female reproductive openings (a) which are in the mantle cavity on the right side of the body, beneath the reduced shell near the rear of the body

As in the Anaspideans, the aglajids, and most other cephalaspideans, have a sperm groove (b) which runs from the genital openings at the rear forward to the penis

It is therefore physically impossible for mating partners to act as both male and female at the same time.


Aplysia parvula

They sometimes mate in chains, but they also mate in pairs with one acting as a male, the other as a female.


Aplysia parvula

by Philibert Bidgrain

Souris blanche lagoon, Trois Bassins, on a beach rock, less 1 m, 8 December 2006.

They mate "head to tail".

This can lead to them forming mating chains where three or more animals mate simultaneously, the ones in the middle being simultaneously male and female.

The animal acting as "male" lying down on top of the hidden shell and mantle cavity of the "female" so that its penis, which is on the right side of the head, can enter the genital opening of its partner which is directly below where it is lying.