• Question: i was on a website and it said this 'Jellyfish are made up of over 95% water, and they do not have brains, hearts, gills, bones, or blood.\\\' if that is true how do they work without a brains a heart?

    Asked by mayawright to Meeks, Pete, Stephen, Steve, Tom on 22 Jun 2010 in Categories: .
    • Photo: Stephen Curry

      Stephen Curry answered on 21 Jun 2010:

      Well I’m not sure but I think they will have a nervous system of some sort, which at least controls the muscles that allow them to swim. But it may not have to be very sophisticated.

      What do jellyfish do apart from floating around all day long bumping into food (microscopic plankton)? You don’t need much of a brain to do that (I imagine)!

    • Photo: Marieke Navin

      Marieke Navin answered on 22 Jun 2010:

      Hey Maya – jellyfish scare me SO BAD!! I was scared to death of getting stung by one in Australia, but luckily I didn’t. The thing with jellyfish is they have a completely different physiology to us. I’m just doing a bit of googling myself here. So they don’t need lungs because they get their oxygen by osmosis, therefore they don’t need blood, therefore don’t need a heart….they don’t even have a brain but a “loose network of nerves” YUCK!

    • Photo: Tom Hartley

      Tom Hartley answered on 22 Jun 2010:

      There are many organisms (bacteria, amoeba etc.) which manage fine without a brain or circulation. For this to work you need to be relatively small (so oxygen can get through to all parts of the body) and to have a simple body, with simple but effective behaviour. The brain is useful for more complex behaviours which need to adapt to changing situations (through learning), but it is quite a costly organ (it uses a lot of energy, even when you are not moving about).

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