Economy of arm autotomy in the mesopelagic squid Octopoteuthis deletron

Abstract

Remotely operated vehicles (ROVs) wer e used to obser ve and collect the meso - pelagic squid Octopoteuthis deletron Young, 1972. I documented numer ous individuals with shortened, blunt-ended arms and regenerating arm-tips, which may be indicative of ar m autotomy, i.e. the jettisoning of a body part as a defense. To test the hypothesis that O. deletron is capa ble of arm autotomy, laboratory investigations and an in situ experiment using ROVs attempted to induce autotomy. I looked for autotomy fractur e planes in histologically sectioned ar ms. O. deletron is capable of ar m autotomy, but it r equires 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 ar m anywhere along its length, only a few well-defined frac ture planes were found in our histological sections, indicating that autotomy pr obably occurs via loss of tensile strength during a defensive interaction. In O. deletron, an autotomized arm usually thrashes and the ter minal arm photophore bioluminesces-whether a steady glow, flashing on and off, or both-which could be an impor tant 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 ver y few species known to use attack autotomy, whereby a predator is grasped by a body part that is subsequently autotomized. © Inter-Research 2012.