| Summary: | Among the seven recognized but poorly defined species belonging to the genus Octopoteuthis (Decapodiformes, Octopoteuthidae), only O. sicula Rüppel, 1844, traditionally, has been reported in the Mediterranean Sea, even though the presence of O. megatera has been suggested, recently. Morphological identification of the species within this genus is based primarily on the presence, number and position of photophores. Recent findings pointed out discrepancies between some well acknowledged species-specific key-guidelines available in the literature for these features and what has been observed in specimens from the Mediterranean Sea, generally referred to as O. sicula. In particular, the absence of photophores observed in specimens from the Sicilian waters – i.e., the locus typicus of O. sicula - and the presence of additional visceral photophores observed in specimens from Sardinian waters and from the Aegean Sea are noteworthy. Such discrepancies suggest that the situation of the genus Octopoteuthis in the Mediterranean is more complex than previously acknowledged and cast doubts on the validity of the main characters traditionally used to differentiate among the species. In an attempt to clarify the situation, specimens from various Mediterranean locations (i.e., Turkish waters, Aegean Sea, Ionian Sea, Sicilian Channel, Sardinian waters, Ligurian Sea) were gathered and their morphology re-examined. Beaks and tissue sample adequately preserved for molecular analysis were also collected for examination. In addition, beaks attributed to O. sicula obtained from stomach contents of cetaceans stranded in the Canary Islands (northeast Atlantic) as well as morphometric data of O. sicula specimens collected from South African waters were gathered, examined and analyzed for comparison with those of Mediterranean specimens. A multivariate analysis of morphometric data was carried out on the available sample (i.e., a total of 50 specimens, 33 of which from South Africa Atlantic waters) as a preliminary discriminating ...
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