MEPS 458:133-140 (2012)  -  DOI: https://doi.org/10.3354/meps09714

ABSTRACT: Remotely operated vehicles (ROVs) were used to observe and collect the mesopelagic squid Octopoteuthis deletron Young, 1972. I documented numerous individuals with shortened, blunt-ended arms and regenerating arm-tips, which may be indicative of arm autotomy, i.e. the jettisoning of a body part as a defense. To test the hypothesis that O. deletron is capable of arm autotomy, laboratory investigations and an in situ experiment using ROVs attempted to induce autotomy. I looked for autotomy fracture planes in histologically sectioned arms. O. deletron is capable of arm autotomy, but it requires traction to occur. O. deletron has numerous places where an arm can sever; arm breakage always occurred immediately proximal to the point of interaction, minimizing tissue loss, and demonstrating ‘economy of autotomy’. Despite the fact that this species can autotomize an arm anywhere along its length, only a few well-defined fracture planes were found in our histological sections, indicating that autotomy probably occurs via loss of tensile strength during a defensive interaction. In O. deletron, an autotomized arm usually thrashes and the terminal arm photophore bioluminesces—whether a steady glow, flashing on and off, or both—which could be an important part of predator distraction associated with autotomy in dark, mesopelagic waters. O. deletron is the first squid reported to autotomize its arms, the only cephalopod known to be capable of economy of autotomy, and is one of very few species known to use attack autotomy, whereby a predator is grasped by a body part that is subsequently autotomized.

KEY WORDS: Cephalopod · Autotomy · Economy of autotomy · Attack autotomy · Bioluminescence · Defense · Mesopelagic