How do octopuses autotomize or lose their arms?

To understand the mechanisms behind arm autotomy, specifically in a soft bodied organims, I looked for pre-formed autotomy planes and zones of weakness present in A. aculeatus arms. I produced and analyzed histological sections throughout the length of each arm to find pre-formed cleavage planes and measured the force required to autotomize octopus arms using an Instron ® to find zones of weakness. I also investigated the potential role of the central nervous system in regulating autotomy using decerebrations to isolate the influence of the supraesophageal mass, implicated in effecting higher cognitive processes like learning and memory.

Is octopus arm autotomy an ecologically relevant behavior?

Autotomy is a secondary defense mechanism that is commonly used by a wide variety of animals, as demonstrated by the frequency of encountering individuals with lost limbs and body parts.Evaluating the incidence of appendage loss in the wild is a first step to better understanding the relative importance of secondary defense mechanisms. I observed octopus A. aculeatus in the coral reefs of Cebu, Philippines to determine its frequency of autotomy and to distinguish important abiotic and biotic factors in the habitat that may affect this occurrence. 

Is losing an arm (or two) costly to octopus locomotion?

Autotomy, although immediately beneficial to the escape and survival of an individual from a predator’s grasps, can be costly to locomotion, foraging activities, and reproduction. To assess the costs of autotomy to locomotion, I looked at the speed and modes of used in A. aculeatus before and after losing an arm. The most common and fastest modes of locomotion are crawling and jetting, respectively. The autotomized arm may also have the added benefit of distracting the predator with excessive movement. These were tested with behavioral assays using their natural fish predators.