I am afraid I know nothing of this species. I have the following reference but unfortunately don't have a copy of it. If anyone has photos of it, or further information, which they could send to the Forum, I would be very grateful.
• Perrone, A.S. (1990) Una nuova specie di Elysiidae, Elysia hetta nov. sp. dal litorale salentino (Mediterraneo, Golfo di taranto) (Opisthobranchia: Sacoglossa). Atti Soc. It. Sci. Nat. e Mus. Civ. St. Nat. Milano, 130(18): 249-252
Rudman, W.B., 2004 (March 7) Elysia hetta Perrone, 1990. [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/elyshett