The reader should first be introduced to the term “Lessepsian migration”, which is as yet of only limited circulation. The term was coined (Por, 1969a, 1971b) when it became evident that the unidirectional migration of the Red Sea species to the Mediterranean via the Suez Canal is a unique phenomenon in modern biogeography. This uniqueness in the dimensions and directionality of the migration through the Suez Canal needed a short and diagnostic name. As such, “Lessepsian migration” is a phenomenon of unidirectional and successful biotic advance from the Red Sea to the Eastern Mediterranean. It does not include migrational happenings which occurred through passive transport to harbors far from the Canal; nor does it include the rather isolated cases of migration in the opposite sense: from the Mediterranean to the Red Sea. Finally, it does not include the many cases of migration into the Canal, though many of such species might be future Lessepsian migrants.