Upside-down jellyfish and their grenades


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Cassiopeia jellyfish (aka "upside-down jellyfish") used to be very popular in the hobby since they are "easy to keep" jellyfish (they do not require a kreisel setup, and are photosynthetic).

It has been discovered recently that they eject a mucus that is used as grenades to kill small preys, and seems to be responsible for itchy skin while swimming in an area where they exist, or even in aquariums.

You can read about it here:

Interestingly, this phenomenon had not been described in details by scientists before, but seemed to have been well known by hobbyists. Aka we should grab a microscope and publish more! The following statement is from 10 years ago!

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