Spotlight: Octopus Hypnosis and Arm Electrode Implantation
We have explored the use of octopus hypnosis as an alternative to the more commonly-used ethanol anesthesia. Octopus “hypnosis” was first described by Vasily Danilewsky, and then J. Ten Cate, as a temporary sleep-like still state in the octopus, induced by keeping the octopus with its oral side up. In this calm, relatively stationary state, there are mainly only local responses to sensory stimuli or local anesthesia injections (magnesium chloride). Notably, efficacy of hypnosis seems to vary with octopus age and size, with senescent octopuses being least affected by it. Hypnosis is much preferable to ethanol anesthesia in many instances, as recovery from hypnosis is much quicker and easier, it prevents sluggish and aversive behavior often accompanying ethanol anesthesia, and it may also prevent the potential ethanol-induced, cytotoxic tissue damage which interferes with electrophysiological recordings. We have successfully used the octopus hypnosis procedure combined with local anesthesia, for behavioral studies and arm electrode implantation.

Octopus rubescens hunting and camouflage
Octopus hunting behaviors are shaped by both instinct and experience. Here, an adult Octopus rubescens attempts to capture a shrimp. In the first few attempts, it misses, and on the fourth, it appears to predict the movement of the shrimp for a successful capture. It then drops down to the substrate and camouflages, changing its skin coloration and texture to match that of its environment, by controlling the sizes of its chromatophores (pigment-containing cells) and papillae. This type of camouflage behavior is typical after prey capture.


Isolated octopus arm responses to chemical and tactile stimuli
(Recorded by Colin Lee and Katya Gribkova.) In an isolated octopus arm, shrimp juice was pipetted onto individual suckers. In the first video, a single sucker initially reacts to the shrimp juice stimulus, reaching towards the source, followed by a neighboring sucker reaching towards it as well. This suggests that an individual sucker may be capable of locating the source of a chemical stimulus through its sensory network and reach towards it, possibly recruiting neighboring suckers in the process.

Shrimp juice stimulation, combined with tactile stimulation from the pipette, can result in greater movement and more complex responses. In this second video, these combined stimuli seem to elicit greater recruitment of neighboring suckers in a distal part of the isolated octopus arm, followed by bend formation at the site of stimulation.


Octopus interacting with Flabellina

Navanax Feeding
The recent El Niño phenomenon warmed the waters of Monterey Bay to the point where a substantial population of the predatory cephalospidean Navanax inermis was recruited, which was feeding voraciously on the pretty little aeolid nudibranch Hermissenda crassicornis. While in the bay region, we were pretty impressed with the feeding behavior of Navanax and made this video. The actual strike, where now-you-see-Hermissenda-now-you-don’t, takes less than 200 msec (4 video frames). Others have shown that this happens through a rapid muscular expansion of the slug’s pharynx, causing a vacuum cleaner effect.

Pleurobranchaea one trial learning
The receding El Niño also left a population of the spectacular aeolid nudibranch Flabellina iodinea, or the Spanish Shawl, in Monterey Bay eating the hydroid Eudendrium. By accident, we found that Flabellina was one of the few animals that Pleurobranchaea will attack, then spit out. R.-C. Huang located the noxiousness of Flabellina to its bright orange cerata. Aeolids are famous for their habits of eating corals, anemones and hydroids and selectively preserving their stinging cells (nematocysts) for use in their own defense, mysteriously transporting and embedding the nematocysts in the cerata.

As shown in the video, we found that a single trial exposure of Pleurobranchaea to Flabellina can result in prey-avoidance learning in just a single trial: shown are two encounters separated by 1/2 hour. An attack by Pleurobranchaea is followed by rejection of the Spanish Shawl, which goes into escape swimming. The frustrated predator shows repeated cycles of rejection movements with its radula and jaws, then performs a stereotypic avoidance turn and locomotes the hell oudda there. In the next shot, 30 min. later, Pleurobranchaea‘s avoidance turn occurs on contact with the mucus of the nearby Flabellina. The prey-avoidance learning seems pretty selective: while experienced Pleurobranchaea avoid Flabellina, they continue to eat the related aeolid Hermissenda like popcorn and their feeding thresholds to stimulants like trimethylglycine are unchanged. The aeolidCoryphella sp. acts like Flabellina in training Pleurobranchaea in prey avoidance. Occasionally Coryphella comes up in the same trawls with Pleurobranchaea, indicating that they are sharing the neighborhood in the abyss, the Pleurobranchaea avoidCoryphella without further laboratory exposure.

Pleurobranchaea feeding # 1

Feeding behavior in Pleurobranchaea consists of initial searching displayed by locomotion, “sniffing” orienting movements of the proboscis and extension of the oral veil. Once food is localized, the mouth opens to expose teeth which bring the food to the mouth. Proboscis protracts and retracts repeatedly to facilitate the motion of the food to the mouth and the gut. On the initial phase of proboscis retraction swallowing occurs.
In this clip Pleurobranchaea performs the initial searching behavior as it moves down the tank wall. It then orients on a piece of fresh shrimp on the base of the tank and proceeds to consume it.

Pleurobranchaea feeding #2
Feeding behavior in Pleurobranchaea is as above but without the prominent searching behavior.

Pleurobranchaea locomotion
Pleurobranchaea‘s locomotion relies heavily on mucus secretion which facilitates a ‘pedaling’ behavior of cilia on the foot.

Pleurobranchaea mating
Sexula behavior of Pleurobranchaea consists of 4 phases:
1. mate detection
2. approach
3. body orientation (side by side facing in opposite directions)
4. engagement of male and female sexual organs (the animals are hermaphroditic)

During the last 3 phases, the animals assume a specific and highly characteristic sexual posture, consisting of:
– upward curling of the right edge of the mantle to expose gill and sexual organs
– unfurling and rearward extension of the gills
– partial to complete extension of the sexual organs
See Davis and Mpitsos, J. A. vergl. Physiologie 75, 207-232, 1971.

Pleurobranchaea turning
There are at least two types of turning behaviors observed for Pleurobranchaea. The orienting turn is usually slower and consists of twisting the foot by contracting the bodywall muscles. Avoidance turning is more vigorous; higher turning speed is achieved by raising the front portion of the foot and swinging around “on the heel”.