Vacant Greenhouse: Phyllodesmium opalescens

Phyllodesmium opalescens

Is this nudibranch transparent because it wants to be invisible--or is it just easier not to add pigment? (I understand that the second is why cars are a little less expensive if they are white -- so that almost all government-purchased cars are white). Many species in this genus take their transparency a step further, and maintain an internal garden of photosynthetic single-celled organisms (zooxanthellae). They obtain these organisms from their prey, and depend on them as a source of nutrition. It would be sort of like raiding someone's greenhouse to stock your own -- and then eating them. However, the species opalescens leaves its greenhouse empty. Their diet is unknown.

Phyllodesmium opalescens, with eye spot.

Phyllodesmium opalescens, also with eye spot.