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Intro to Octopuses
Octopuses are members of the class Cephalopoda.The cephalopods are a diverse class of mollusks that emerged during the Cambrian period more than 500 million years ago.
Today, there are two major groups of cephalopods called subclasses: 1) Nautilodea, 2) Coleoidea. The Coleoidea comprises two superorders: 1) Octopodiformes, 2) Decapodiformes. Octopuses are members of the Octopodiformes.
Today, there are roughly 300 species of octopuses, but this number is continuously increasing as new species are discovered.It is estimated that there are about 60- 70 species in the seas around Japan.
Octopuses are exclusively marine. They occur at all latitudes from the equator to polar waters.
There are two groups of octopuses: 1) the finless incirrate octopuses (suborder Incirrata), 2) the semi-gelatinous finned cirrate octopuses (suborder Cirrata). One member of the Incirrata suborder is the giant Pacific octopus.
Intro to Giant Pacific Octopus
Here in Hokkaido, the best known octopus is the giant Pacific octopus (Enteroctopus dofleini). It is the world’s largest octopus and the most abundant species in coastal waters of the North Pacific. It occurs along the Pacific Rim from Baja California, Mexico, to the Gulf of Alaska, Aleutian Islands, Bering Sea, Sea of Okhotsk, and Sea of Japan.
Its maximum lifespan is thought to be about 4.5 years in males and 5 years in females.
In Japan, it is the most commercially important octopus species; annual catches total around 15,000-20,000 t, with most coming from coastal waters in Hokkaido.
External Characteristics
Octopuses have three main body parts: 1) the arms surrounding the mouth, 2) the head, which includes the eyes, and 3) the sac-like mantle.
Let’s first look at the arms.
Arms
Octopuses have eight arms; they are used for a variety of tasks including walking and handling objects. About two-thirds of an octopus’s neurons are located in their arms. As a result, each arm can operate almost independently.
Suckers
An important feature of the arms are suckers. In MIZUDAKO, there are two rows of suckers on each arm. In adults, each arm has about 96-106 suckers. Suckers are complex organs that are used for movement, attachment, feeding, tasting, and displays. Octopuses frequently shed the skin layer covering each sucker; Sometimes octopus briefly twirl their arms, which is called the “octopus dance”. This behavior might help them help shed this layer of skin.
Skin
Octopods have remarkable skin that can change color and texture. The components produce the color of the skin include 1) chromatophores, 2) iridophores, and 3) leucophores. Chromatophores are like small balloons of pigment. They come in different colors including yellow, orange, red, brown and black. The physical texture of the skin is controlled by a complex musculature. The skin can be either smooth or very spiky. These peaks in the skin are called papillae. In combination, these skin components can produce complex visual displays that are used for camouflage.
Eyes
Octopuses have well-developed eyes and excellent vision. Evidence from retinal structure and behavioral experiments suggests octopuses are color blind. However, the elongate shape of the pupil might allow them to detect colors. Octopus, squid, and cuttlefish each have differently shaped pupils - an octopus has a rectangular pupil, a cuttlefish has a w-shaped pupil, and a squid’s pupil is circular. The octopus pupil is bound by the iris. The iris has a layer of chromatophores. Species have also been demonstrated as discriminating the plane of polarization of polarized light. This can be used to help detect prey and predators.
Locomotion
Octopuses move around using several methods. The most common is crawling along the bottom. The front two pairs of arms are often raised off the seafloor. While the rear two pairs propel the animal forward. When foraging, an octopus normally crawls, but uses the front two pair of arms to probe under rocks and into crevices to search for food. Interestingly, octopuses in southern Hokkaido are often missing parts of the front two pair of legs. This is most likely due to attacks by predators. Fortunately for the octopus, they can regenerate new arms (and suckers!) if they are lost.
Another form of locomotion is jet propulsion. Water is drawn into the mantle and forced strongly out the funnel. This is often used when trying to escape from a predator. Jet propulsion allows the octopus to accelerate quickly, but is inefficient in terms of the energy expended.
When trying to escape, octopuses will also eject ink towards an attacker.
Defensive behavior
Octopuses have evolved many ways to defend themselves from predation. They have two general defensive strategies: primary defense and secondary defense. Primary defense decrease the chances of encountering or being detected by a predator. The common primary defenses of octopuses include camouflage and crypsis. The octopus can take on the appearance of the substrate or background using its remarkable skin.
When an octopus has been detected or recognized, it might adopt a secondary defense, such as fleeing while producing a large “smoke screen” of ink to distract the predator.
Foraging and feeding
Like other cephalopods, octopuses are carnivores. Prey are diverse and include crustaceans, teleost fishes, and shelled molluscs. Also, like many other cephalopods, there is a prevalence of cannibalism! In octopuses the web between the arms is important in prey capture. It is spread and used to envelop prey. MIZUDAKO conducts what is called “speculative hunting”. They pounce with an outspread web and then feel around under the web for food. Any prey are then transferred to the mouth by the suckers. The octopus also extend its front two pairs of arms into crevices to locate food (“speculative groping”). This could explain why the tips of these arms are often missing.
Octopuses cannot swallow whole large prey as most fishes and mammals do. The esophagus passes through the center of a donut-shaped brain. Prey is macerated into small pieces in order to pass through the center of the brain.
Respiration
Octopuses breathe by drawing water into the mantle cavity through gill slits on both sides of the head. Water passes over the gills, where oxygen is exchanged with carbon dioxide. The blood of octopuses (like other cephalopods) is blue due to copper-rich protein called hemocyanin, which transports oxygen from the gills to the rest of the body.
Reproduction
Males use a modified arm (hectocotylus) to pass encapsulated packages of sperm (spermatophores) to females. During mating, the male inserts the tip of the hectocotylus into the female’s oviduct opening within the mantle cavity. The males passes an elongated package of sperm called a spermatophore, which can be up to 1 m long. The transfer of sperm can last 2-4 hours.
Once she has mated, she locates a den for holding her and the eggs she will lay. Once the eggs are laid, she will groom and protect the eggs for 7-11 months! During this time she remains in the den and does not feed. Most incirrate octopods spawn once and die around the time that the eggs hatch.
Sleep
Recent research in Brazil found that octopus have two distinct stages of sleep: quiet sleep and active sleep. The active sleep stage appears similar to REM sleep in humans. We do not know if the giant Pacific octopus also sleeps, but a student is now studying this topic at the Usujiri Fisheries Sation.
BOWER John Richard・Faculty of Fisheries Sciences, Hokkaido University・Associate Professor
Further readings
Hanlon, R., Vecchione, M., & Allcock, L. 2018. Octopus, Squid, and Cuttlefish: A visual, scientific guide to the oceans’ most advanced invertebrates. University of Chicago Press.
Arms and Suckers
Reardon S. 2023. How octopuses taste with their arms. Nature. 2023 Apr 12.
Skin
Hanlon, R. (2007). Cephalopod dynamic camouflage. Cur. Biol. 17: R400-R404.
Eyes
Locomotion
Hanlon, R. T., & Messenger, J. B. 2018. Cephalopod behaviour. Cambridge University Press.
Defensive behavior
Hanlon, R. T., & Messenger, J. B. 2018. Cephalopod behaviour. Cambridge University Press.
Foraging and feeding
Hanlon, R. T., & Messenger, J. B. 2018. Cephalopod behaviour. Cambridge University Press.
Reproduction
Hanlon, R. T., & Messenger, J. B. 2018. Cephalopod behaviour. Cambridge University Press.
Sleep
de Souza Medeiros, S. L., de Paiva, M. M. M., Lopes, P. H. et al. 2021. Cyclic alternation of quiet and active sleep states in the octopus. iScience 24:102223.
Gutnick, T., Rokhsar, D. S., & Kuba, M. J. 2023. Cephalopod behaviour. Cur. Biol. 33:R1083-R1086.
Meisel, D. V., Byrne, R. A., Mather, J. A., & Kuba, M. 2011. Behavioral sleep in Octopus vulgaris. Vie et Milieu, 61:185-190.
26 November 2023 posted
BROKEN
When I was getting used to life in Hakodate, I was often told by the owner of a sushi restaurant that we can have absolutely delicious octopus made by a master chef using boiled octopus who lives in a town on the eastern coast of southern Hokkaido. Octopus? not squid, in Hakodate? At that time, more than 20 years ago, I had no idea that research on octopus would begin to develop in Hakodate. Associate Professor Bower, Faculty of Fisheries Sciences, Hokkaido University, has switched from squid ecology to octopus ecology, breaking new frontiers in octopus research. As you may have noticed, this octopus content breaks with conventional style, changing the title of the Welcome Photo, and composing the monotone main body using a combination of video and text. We also decided to place the FoM editorial essay at the end, smoothly entering the world of octopus.
We hope that you will enjoy the world of octopus that Associate Professor Bower has created. From autumn to early spring is the best seasons for octopus in Hakodate. We hope you will try the excellent Hakodate octopus, which opens up a new world of taste and texture.
FoM Editorial
26 Novermber 2023
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