1. You may have heard that octopuses are colorblind because they only have one kind of photoreceptor in their eyes. But did you know that recent studies may be able to explain how cephalopods could still perceive color due to the odd shape of their pupil? It’s true. Researchers at UC Berkley, Cambridge and Harvard have analyzed the shape of cephalopod pupils and the depth of the retina and modeled how the animals may be able to distinguish different wavelengths of color by controlling which wavelengths are focused on their retina at any given time. An article recently published in the Proceedings of the National Academy of Sciences may be the first part of a larger explanation for how seemingly colorblind animals can match their colors so well to the surrounding environment.
2. An octopus has a pair of organs called statocysts, sac-like structures lined with hairs, located near the brain. These are balance organs which help the octopus orient itself and maintain its position in the water. Some researchers have hypothesized that statocysts contribute to the octopus’s ability to sense vibrations, especially at lower frequencies.
3. You may know about chromatophores, cells that mechanically expand and contract, exposing different pigments to filter light. But have you heard of leucophores and iridophores? Leucophores act like diffusers to spread light to a greater area, while iridophores have ridges that structurally bend and reflect light, causing iridescent colors.
4. The common octopus, Octopus vulgaris, has been observed to untie surgical silk with its suckers.
5. Octopus muscles do not constrict. Their suction cups are capable of great suction and their muscular arms can pull with strong force, but if an octopus wrapped its arm(s) around you, you wouldn’t be in danger of suffering circulatory arrest, as you might with a boa constrictor.
6. Some octopuses can see with their skin. Opsins are light-sensitive proteins that are found in the eyes of some octopuses, as well as in their skin. Scientists from UC Santa Barbara discovered that a California two-spot octopus’ chromatophores respond to changes in light, without any light being detected by the eye. That implies that some camouflage is accomplished without being controlled by the eyes or brain.
7. While most octopuses are presumed to be loners, the Pacific striped octopus has been observed to exhibit social behavior, including living in groups. This species is also somewhat unique as one of only two octopus species that have been observed to lay more than one batch of eggs (the other is the closely related lesser Pacific striped octopus).
8. A tiny mesozoan, or parasitic worm, called Dicyemennea nouveli selectively inhabits the renal sacs of giant Pacific octopuses. The worm has no internal organs other than reproductive cells. It burrows one end into the tissue of the host’s kidney and directly absorbs dissolved nutrients. There are many other documented cases of kidney parasite species preferring specific cephalopod hosts.