Ventral adhesive area in the limbs of walking cuttlefish (paintpot cuttlefish, Ascarosepion tullbergi): An adaptation for stable aquatic locomotion

Walking is a locomotion mode in which animals move over the ground using their appendages. Walking is observed in both terrestrial and aquatic animals, but the morphology and diversity of appendages in the latter group have been less extensively studied. The present paper reports on the “adhesive areas,” which may represent morphological and physiological adaptations for stable aquatic walking, in the paintpot cuttlefish, Ascarosepion tullbergi. This animal employs arm IV as a forelimb and an ambulatory flap as a hindlimb for walking, resulting in a gait-like manner of movement. The structure of the adhesive area is exclusively located on the ventral skin surface of arm IV and the ambulatory flap, which are in contact with the ground during walking. The “adhesive areas” are characterized by a dense population of adhesive mucus-secreting cells and the development of numerous wrinkles on the surface. These features may enhance the gripping and sticking capacity of the ground-contact area, thus improving walking stability. The use of adhesive areas for walking is a unique feature of A. tullbergi, as other cuttlefish with adhesive areas primarily use them for attaching to substrata in strong currents. Our results contribute to the understanding of the locomotion strategy of cuttlefish.