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Round 3 - Cephalopoda - Octopoda

(Sources - 1, 2, 3, 4)

Order: Octopoda

Common Name: “octopus” (pl: “octopuses” or “octopodes”)

Families: 14 - Cirroteuthidae , Stauroteuthidae, Opisthoteuthidae (“umbrella octopuses”), Cirroctopodidae, Tremoctopodidae (“blanket octopuses”), Alloposidae (“Seven-arm Octopus”), Argonautidae (“argonauts” or “paper nautiluses”), Ocythoidae (“Tuberculate Pelagic Octopus”), Eledonidae, Bathypolypodidae, Enteroctopodidae, Octopodidae, Megaleledonidae, and Amphitretidae

Anatomy: eight arms fully or partially encased in webbing ; suckers line the inside of arms; two rear appendages are generally used to walk on the sea floor; slit-shaped pupil; no internal shell; most of the body is made of soft, gelatinous tissue allowing it to squeeze through tiny gaps; many species can change color, texture, size, and shape to camouflage and communicate

Diet: crustaceans, other mollusks, and fish

Habitat/Range: every ocean, with species adapted to many habitats, including tide pools, coral reefs, seagrass beds, open ocean, the Antarctic, and hydrothermal vents

Evolved in: Middle Jurassic

Do you have a favorite in Octopoda?

One or more of my favorite animals is in Octopoda

I love at least one or more of these animals

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I dislike all of these animals

Voting ended onJun 5, 2025

Propaganda under the cut:

The Argonauts (genus Argonauta, the only living genus in the family Argonautidae) (image 4) build their own paper-thin shells to use as a brood chamber and maintain buoyancy. This shell is not related to the external shell of nautiluses or the internal shell of squids. Nevertheless, argonauts are sometimes referred to as “Paper Nautiluses” due to this shell.

Colour vision appears to vary from species to species, for example, it is present in the Marbled Octopus (Amphioctopus aegina) but absent in the Common Octopus (Octopus vulgaris). Octopuses achieve their color-changing camouflage by using opsins in their skin which respond to different wavelengths of light and help the animals choose a colouration that matches the surroundings. Chromatophores in the skin can also respond to light independently of the eyes. An alternative hypothesis is that cephalopod eyes in species that only have a single photoreceptor protein may use chromatic aberration to turn monochromatic vision into colour vision, though this lowers image quality.

Most octopuses are solitary, but the Larger Pacific Striped Octopus (Octopus sp.) has been described as particularly social, living in groups of up to 40.

On rare occasions, octopuses hunt cooperatively with other species, with fish as their partners. They communicate with their partners by punching them.

All octopuses are venomous, but only the genus Hapalochlaena (Blue-ringed Octopuses) (image 3), has venom that is lethal to humans. The genus consists of four species of octopus that are found in tide pools and coral reefs in the Pacific and Indian oceans, from Japan to Australia. Despite their small size (12 to 20 cm [5 to 8 in]) they carry enough neurotoxic venom to kill 26 adult humans within minutes. The venom can result in nausea, respiratory arrest, heart failure, severe and sometimes total paralysis, blindness, and can lead to death within minutes if not treated. Death is usually from suffocation due to paralysis of the diaphragm. Despite this, Blue-ringed Octopuses are relatively docile and will only bite if actively harassed, instead choosing to flee or display their warning colors: bright yellow with blue flashing rings. Very few deaths have been recorded.

The Giant Pacific Octopus (Enteroctopus dofleini) (image 1) is often cited as the largest octopus species. Adults usually weigh 10–50 kg (22–110 lb), with an arm span of up to 4.8 m (16 ft). The largest specimen of this species to be scientifically documented reached a live mass of 71 kg (157 lb). Much larger sizes have been claimed: one specimen was recorded as 272 kg (600 lb) with an arm span of 9 m (30 ft). However, one carcass of a Seven-arm Octopus (Haliphron atlanticus), weighed 61 kg (134 lb) and was estimated to have had a live mass of 75 kg (165 lb).

The Star-sucker Pygmy Octopus (Octopus wolfi) is the smallest known octopus, at a length less than 2.5 cm (1 in) and a weight less than 1 g (0.04 oz).

The Coconut Octopus (Amphioctopus marginatus) collects discarded coconut shells, then uses them to build a shelter, an example of tool use.

Octopuses are highly intelligent. Maze and problem-solving experiments have shown evidence of a memory system that can store both short- and long-term memory. In laboratory experiments, octopuses can readily be trained to distinguish between different shapes and patterns. Octopuses have also been observed in what has been described as play: including moving around a bottle by jetting water at it. Octopuses often break out of aquariums and sometimes into others in search of food, after which they return to their enclosure.

Evidence indicates that octopuses are sentient and can feel pain.

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