The State of the Art of the Global Distribution of the Invasive Mytilid Species <i>Brachidontes pharaonis</i> (P. Fischer, 1870)

The studies on the bioinvasion phenomenon focus mainly on the biological and ecological traits of a species, while scattered literature is addressed to a correct systematic assessment and an updated geographical distribution on the whole. It is noteworthy that non-indigenous species should be monitored on both sides of their range, i.e., towards the front of dispersal and beyond the original range. The backside range boundaries are not often monitored or well delimited; thus, the novel global distribution of an invasive taxon is not often accurately delimitated. A model species for highlighting criticisms about the scarce knowledge on the novel range was chosen. <i>Brachidontes pharaonis</i> is a mussel that has successfully colonised the Mediterranean Sea, following an immigration pathway through the Suez Canal from the Red Sea, presumably from a wider Indo-Pacific area. In this case, the Indo-Pacific boundaries have been overlooked and are still misunderstood due to diverse causes, principally as the synonymy with the congeneric <i>B. variabilis</i> has created confusion in the taxonomic identification. The present review demonstrates that the borders of the <i>B. pharaonis</i> range are still unclear and that the species should be analysed in a wider geographical area. Records of <i>B. pharaonis</i> from Southeast Asia should be treated with caution as this area is out of its range. The Indian and Pacific Oceans host the taxon <i>B. variabilis</i>, composed of two potential cryptic species. Data from the literature highlight the importance of the integrative taxonomic approach to solving various issues concerning the species group complex, morphological variations and cosmopolitan claims of species.