Indo-West Pacific. Reported to have migrated into Mediterranean through Suez Canal.
Notarchus is a genus of Sea Hare in which the parapodia are almost completely fused. There is a small anterior opening to allow an exchange of water to the mantle cavity. They have no shell. They are able to escape from danger by swimming by jet propulsion.
There are two described species, Notarchus punctatus with an armed penis and Notarchus indicus without. N. punctatus is recorded from the Mediterranean, Caribbean and curiously Japan. Notarchus indicus is known from much of the Indo-West Pacific under various names.