Fact 1: Tunicates reproduce sexually.

Fact 2: Tunicates are sea creatures encased by tough membranes, reminiscent of tunics.

Given the two facts above, answer the question "Sea creatures encased by what reproduce sexually?" with the following options: 
- barnacles
 - refraction of light
 - layers of fat
 - Epidermis
 - tough membranes
 - ocean water
 - gastropod shells
 - epidermis and dermis


 

     tough membranes    