How do sea urchins hang on upside-down on the bottom of floats?
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| Green sea urchins, Strongylocentrotus droebachiensis, on the underside of a float. |
It always looks impossible; those spines don't stick to anything. But I've watched them in my aquarium; on the mouth side, which is the uppermost side in this photo, in among the spines, they have thin tube feet. The tubes, with a suction cup on the end, can extend beyond the spines; with them, they can walk about, just as a starfish does.
They use the feet to attach themselves to underwater structures, and also to capture food particles and move them towards the mouth.
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| Small sea urchin, in my tank, showing off its tube feet. Oct. 2019 |
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Los erizos de mar; ¿cómo es que se adhieren a la cara inferior de objetos en el agua? Las espinas que los cubren son redondeadas; no pueden agarrar nada.
Alrededor de la boca, tienen muchos "pies" en forma de tubo, llamados pies ambulacrales. Estos pueden extenderse fuera del alzanze de las espinas. En el extremo, tienen una ventosa que les permite caminar o adherirse, a la manera de las estrellas de mar. También pueden usar los pies para agarrar pequeños objetos flotantes y llevarlos hacia la boca.
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