“You guys made me ink!” is the iconic line from Pearl, the octopus in Finding Nemo. Pearl is a flapjack octopus (genus Opisthoteuthis), and – despite Pixar’s allusion – flapjacks and other deep-sea octopuses are actually unable to use this classic defense mechanism because they lack an ink sac [1]! This is just one of the many features (or lack thereof) that differentiate this fascinating group of octopuses, which contains 24 species found throughout the world’s oceans, from the more common shallow-water octopuses [1, 2].
You may be wondering: isn’t the plural “octopi”? Typically, you will see “octopi” used colloquially. Scientists, however, use the “-es” ending, as the root word “októpous” is of Greek origin, and, therefore, using the Latin plural ending “i” is seen as incorrect. Nevertheless, both endings are generally accepted. Some even throw the correct Greek plural “octopodes” into the mix [3], so call them what you’d like! You may be wondering: isn’t the plural “octopi”? Typically, you will see “octopi” used colloquially. Scientists, however, use the “-es” ending, as the root word “októpous” is of Greek origin, and, therefore, using the Latin plural ending “i” is seen as incorrect. Nevertheless, both endings are generally accepted. Some even throw the correct Greek plural “octopodes” into the mix [3], so call them what you’d like!
Photographed by the Monterey Bay Aquarium Research Institute (MBARI) [Source].
One of the most apt behaviors of the flapjack octopus is their ability to flatten like a pancake, known as “flat-spreading”. The animal outstretches its arms and flattens its mantle (morphology diagram below) to take on a flat, “pancake” like shape [4]. Although this seems like a perfect reason to refer to them as a flapjack, they actually got their name due to the flattened, amorphous shape of preserved specimens. In fact, S. Stillman Berry, who first described the species Opisthoteuthis californiana, referred to them as equal parts “soggy pancake and very dirty floor mop” [5].
Sketch by Comingio Merculiano, 1896 [Source].
These soggy pancakes are often mistaken for another group of finned, deep-sea octopuses: dumbo octopuses (genus Grimpoteuthis), whose large fins resemble the adorable cartoon elephant’s ears. Both are cirrate octopuses, named after the pairs of cirri (slender, hairlike appendages) that line a single row of suckers on each of their eight arms [1]. Cirrate octopuses also have other notable features including a cartilaginous internal shell and a cute pair of ear-like fins on their mantle. This is in contrast to the more “classic” incirrate octopus (think Hank from Finding Dory) that lack fins, cirri, and an internal shell as well as have two rows of suckers and utilize ink clouds for a quick escape.
Additionally, unlike shallow-water coleoid cephalopods (octopuses, squid, and cuttlefish), who have mesmerizing color-changing abilities, cirrate octopuses tend to be a solid orange, red, or purple and unable to change color [1]. This is because many cephalopods change color to blend into their surroundings and communicate [6], a potentially useless ability in the low-light environment of the deep sea where cirrate octopuses inhabit.
Flapjack octopuses are typically found over 300 meters deep, bobbing along on the ocean floor, with some species being found over 2000 meters deep in the perpetually cold and dark bathypelagic, or “midnight”, zone [1]. Due to their deep-sea habitat, they are difficult to observe, and little is known about their natural behaviors. However, a few observational studies have shed light on the behavioral patterns of these octopods, including methods of locomotion, feeding, and defense. For example, while incirrate octopuses use jet propulsion by forcing large amounts of water out of their siphon to move quickly and escape predators, because of their siphon placement and size, flapjack octopuses are not able to effectively use this form of locomotion [7]. Instead, they use medusoid swimming, similar to a jellyfish, by opening and closing their webbed arms to propel them through the water – albeit rather slowly [5, 7]!
And what about those adorable, pigtail-like fins? These pairs of fins move independently of each other in a highly coordinated manner to stabilize and orient the flapjack octopus as it swims and rests on the ocean floor [4, 5].
Photo by MBARI [Source].
Flapjack octopuses’ visual system is not as advanced as other octopuses. Instead, they likely rely on chemoreception and mechanoreception of their suckers and cirri to hunt, primarily feeding on small bristle worms and crustaceans, such as amphipods [8].
Three different feeding behaviors have been described for an unknown species of flapjack octopus (originally misidentified as a dumbo octopus) that was kept in captivity for almost 2 months and fed a diet of brine shrimp [1, 9]. The first is envelopment, during which the animal opens their arms to surround the prey, releasing trapped water slowly through a small hole left at the tips of their arms. It is likely that they use their cirri and/or suckers to prevent the prey from escaping during this process. Second is entrapment, where the animal outstretches their arms, forming a bell-shaped stance, and sinks down to the sea floor, trapping the prey within their arms [9]. It is thought that, once trapped, the cirri and/or suckers aid in moving the prey to their beak. And lastly, the most unique feeding method: cirri-generated, current feeding. This involves coordinated cirral movements towards the mouth, generating slow currents of water that help catch prey and guide them to their demise [9].
Drawings of the three described feeding methods, including
(a) envelopment, (b) entrapment, and (c) cirri-generated current feeding [9].
While little is known about flapjack octopus ecology, they have been found in the stomachs of Patagonian toothfish and sperm whales, as well as in the feces of Australian fur seals [1]. Although it is not known how flapjack octopuses escape or defend themselves from these predators, it is thought that they may use some of the defensive behaviors observed from submersibles and in captivity [1]. One of these is called “web inversion”. This is involves upturning the arms to raise them and the web around the mantle in response to disturbances [4,10]. Another defensive behavior is “ballooning”, where the octopus inflates their web and tucks the tips of their arms under their mantle, creating a spherical shape [4]. It is hypothesized that this sudden, surprising change in body shape might have a stunning or disorienting effect on a potential predator [1].
Images C and D show web inversion, while photos E and F demonstrate the ballooning response [4].
Our understanding of these fascinating deep-sea octopuses has advanced considerably over the last few decades, but many enticing questions remain. For example, we still know very little about their mating behaviors and what their lives are like during the juvenile stage [1]. With technological advancements and submersible expeditions, observing wild flapjack octopuses is becoming more feasible, leading to more answers and – as things tend to go in science – even more questions!
Cover image by NOAA Office of Ocean Exploration and Research, 2019 Southeastern U.S. Deep-sea Exploration [Source].
Written by: Claire Jones is an Animal Behavior PhD candidate in the Animal Behavior and Cognition Lab at UC Davis. Claire’s current research investigates cognitive styles in pigs by examining consistent individual differences in learning and behavior. She has a life-long love of octopuses and completed her undergraduate thesis on numerosity in Octopus vulgaris at the Stazione Zoologica Anton Dohrn.
References:
[1] Collins M.A. & Villanueva, R. (2006). Taxonomy, ecology and behaviour of the cirrate octopods. Oceanography & marine biology: an annual review, 44, 277-322.
[2] Philippe Bouchet (2018). “Opisthoteuthis Verrill, 1883”. World Register of Marine Species. Flanders Marine Institute. Retrieved 28 September 2024.
[3] Should You Say “Octopuses” Or “Octopi”? (2022, March 18). Dictionary.com. https://www.dictionary.com/e/octopuses-or-octopi/
[4] Villanueva, R. (2000). Observations on the behaviour of the cirrate octopod Opisthoteuthis grimaldii (Cephalopoda). Journal of the Marine Biological Association of the United Kingdom, 80(3), 555-556.
[5] Pereyra, W. T. (1965). New records and observations on the flapjack devilfish, Opisthoteuthis californiana Berry.
[6] Ikeda, Y. (2021). Color Change in Cephalopods. Pigments, Pigment Cells and Pigment Patterns, 425-449.
[7] Vecchione, M., & Roper, C. F. (1991). Cephalopods observed from submersibles in the western North Atlantic. Bulletin of Marine Science, 49(1-2), 433-445.
[8] Villanueva, R., & Guerra, A. (1991). Food and prey detection in two deep-sea cephalopods: Opisthoteuthis agassizi and O. vossi (Octopoda: Cirrata). Bulletin of Marine Science, 49(1-2), 288-299.
[9] Hunt, J. C. (1999). Laboratory observations of the feeding behavior of the cirrate octopod, Grimpoteuthis sp.: one use of cirri. The Veliger, 42(2), 152-156.
[10] Packard, A., & Sanders, G. D. (1971). Body patterns of Octopus vulgaris and maturation of the response to disturbance. Animal Behaviour, 19(4), 780-790.
[Edited by Alice Michel]