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Octopus chasing crab

The crab and the octopus; swim faster Mr. crab!!

May 1, 2015 Written by

Come on Mr. Crab. Swim faster. Swim harder. It’s disconcerting to hear the tourists on the boat cheering for the octopus when it catches and kills the crab.

We have seen a lot of crabs and octopus over the years. I feel a little guilty when I think back 25 years ago to crab rodeos and subsequent crab feasts on the back deck of the ship.. We quickly learned that some dungeness crabs are double jointed in which case we had to watch out when we picked them up. These days I just plain feel sorry for the crabs and wish them peace.

We’ve learned a heckuva lot about octopus over the years. Who knew that octo’s have 3 hearts (2 hearts return oxygen depleted blood to the lungs while the 3rd and largest heart pumps oxygenated blood from the gills to the rest of their body)!! Or that their blood is blue. Or that they have the ability to regenerate a limb that is damaged and severed. Or that their digestive system exits the same way their food came in ie. in other words octopus poop is ejected the same way it came in. Kind of makes you think huh…….

Lots of interesting behaviour in this video (aside from the comments from the folks on the surface)…

Octopus have 2 primary modes of locomotion. Octo’s are often seeing crawling along the bottom with such amazing grace that they appear to be gliding along (benefit of having 8 arms to crawl with). In the video we see something quite different – jet propulsion!! The octo draws water in through it’s mantle and then forces it out strongly through it’s funnel (same orifice used for breathing, ejecting ink for camouflage, eating and pooping) channelling it’s direction by snapping 2 of it’s arms together. Cool huh…

What we can’t quite see in the video is what happens to the crab when the octo catches it. Octopus have 2 salivary glands. The posterior (rear) gland secretes a toxin into the water where the prey absorbs it through it’s gills and loses consciousness. In other words, the crab is held inside the interbrachial web of the octo (the “skin” webbing between the arms) where it breathes in a toxin and goes unconscious. The anterior (front) salivary gland secretes enzymes that break down the prey into jelly. Octopus have a parrot like beak and a tongue that looks like a file. So what happens is that the octopus will bite into the crab’s carapace with it’s beak and basically suck out all the jelly like yummy interior parts of crab..

You can see why I was cheering for the crab to swim faster!!!

HINT for divers : you can always tell an octopus kill if you see a distinctive hole in a crab’s carapace from the octo’s beak.

Safe diving.

Captain Mike

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