Octopoteuthis deletron. Image: UC Berkeley

Seems like there’s always a study that comes along once in a while describing yet another peculiar squid ability. The latest was discovered by postdoctoral researcher at the University of Rhode Island who discovered a never before seen defensive tactic in any other type of squid species which involved jettisoning parts of its arm when attacked.

Just one foot long, the squid in question, Octopoteuthis deletron, lives in the deep waters of northeast Pacific Ocean. Stephanie Bush, the lead aquatic researcher involved in the study, first suspected this behavior when she noticed several captured specimens had stumps. Scientists had speculated that they may release their arms, just as lizards can release their tails when attacked, but no one had seen it happen. She embarked on one of Monterey Bay Aquarium Research Institute’s submersibles, which also had a deep-water underwater camera installed, and went on the lookout for specimens to poke. No, really. The submersible’s mechanical arm, which in typical operations is used to grab things, was now instructed to prod some of the squid that were found. Initially, they didn’t come to any conclusive results, but after attaching bottle brush to the arm Bush immediately noticed how poked squids detached arm parts, and convulsively scattered away leaving a small cloud of ink behind it – an ubiquitous defense mechanism present both in squids and octopi.

“The very first time we tried it, the squid spread its arms wide and it was lighting up like fireworks,” she said. “It then came forward and grabbed the bottlebrush and jetted backwards, leaving two arms on the bottlebrush. We think the hooks on its arms latched onto the bristles of the brush, and that was enough for the arms to just pop off.”

The squid are able to re-grow their missing arms, but this mechanisms comes at a great cost, like any defense mechanism.

“There is definitely an energy cost associated with this behavior, but the cost is less than being dead,” Bush said.

The pieces of ejected pieces of arms are bio-luminescent, and keep on moving for a few good seconds after becoming detached. The bio-luminescence is thought to distract enemies or prey while the squid either escapes or attacks. In further experiments, Bush found that some octopus squid appeared hesitant to sacrifice their limbs, but some did so after being prodded several times. Subsequent research showed that the arm bits do grow back, but it takes quite a while, so the squids aren’t inclined to lose them unless absolutely necessary.

Bush’s research on squid began in 2003 when she decided to investigate the assumptions that some scientists had made about deep-sea animals.

“Scientists had assumed that squid living in the deep-sea would not release ink as a defensive measure, but all the species I’ve observed did release ink,” she said. “They assumed that because they’re in the dark all day every day that they’re not doing the same things that shallow water squids are doing. They also assumed that deep-sea squid don’t change color because of the dark, but they do.”

Findings were reported in the journal Marine Ecology Progress Series.