5 cm

This slug was found in rockpool at Mirya, Ratnagiri, in northeastern India.
The area is rocky with sandy patches at an intervals, this area is exposed to open sea directly.

Egg case is also laid in my tank on an alga.

Ref.

http://www.nudipixel.net/photo/00011728/camera/coolpix_s4/
http://www.seaslugforum.net/display.cfm?id=22315