The solitary ascidian Herdmania momus, an Indo-Pacific species that has been introduced into the Mediterranean Sea via the Suez Canal during the past century, has so far been restricted to the Levantine region. Here we record H. momus from the Maltese Islands, which represents a considerable westwards expansion of the species' distribution range in the Mediterranean. Possible modes of introduction are discussed, with translocation of adults via shipping and subsequent spawning at destination sites deemed a plausible mechanism.

One of the most extensively documented marine bioinvasion phenomena is the invasion of Red Sea species to the Mediterranean Sea through the Suez Canal. The present study reports the occurrence of seven non-indigenous ascidian species along the Mediterranean coast of Israel: Ecteinascidia thurstoni, Ascidia cannelata, Phallusia nigra, Rhodosoma turcicum, Symplegma brakenhielmi, Microcosmus exasperatus and Herdmania momus. Five of these species (excluding P. nigra, and R. turcicum) probably reached the Mediterranean via the Suez Canal, since they have an extra-tropical Indo-Pacific distribution and a restricted distribution in the eastern Mediterranean. This is the first record of E. thurstoni in the Mediterranean. The accumulating evidence for the negative impact of non-indigenous ascidians on local species and habitats raises the necessity for long-term studies and monitoring of this group.