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The development of in situ observational tools has significantly contributed to the study of deep-sea cephalopods and exploration of their habitat in the last decades. In this paper, we report in situ observations of rarely observed deep-sea Mediterranean cephalopods (Chiroteuthis veranyi, Chtenopteryx sicula, and Octopoteuthis sicula). These cephalopods were encountered during a scientific expedition, aimed at characterizing the biodiversity of a deep-sea area in the northern Ionian Sea. Images and video were collected by a remotely operated vehicle (ROV) between 537 and 1248 m. Chromatic, postural, locomotor, and bioluminescent behavioral components were reported for each species. This was the first time that O. sicula was filmed in its habitat and all individuals showed hovering and an arm spread posture with the arm tips exposed, producing an intermittent bioluminescence. Furthermore, our observations on six living specimens of C. sicula represent exceptional events, since this species was only observed once in the eastern Mediterranean in 2012. Overall, five females and a mature male of C. sicula were observed; the male had a large dorsal light organ. Finally, an individual of C. veranyi was observed consuming a large lanternfish (Myctophidae). In the near future, in situ explorations in the Mediterranean should be implemented to shed light on deep-sea cephalopods inhabiting this basin and fill information gaps on the biology, ecology, and behavior of elusive species. [ABSTRACT FROM AUTHOR]