Just wondering if a jellyfish has a brain, and if so, where is it located? Beneath the airsac, I wager? And, if there is no actual well-defined brain structure…does it simply have the equivalent of a central nervous system responding strictly to electrochemical impulses without a need for a brain to process such impulses?
The jellyfish doesn’t have a brain, but what’s known as a “nerve net”. It’s just a collection of connected nerves.
No heart either. Just a blob basically 
Pretty much needs a 3-for-1 deal from the Wizzard. …
Of OZ, that is.
OK, on that note…does it have any definitive structures we can call organs, or is it just a blob of various specialized cells, perhaps? Digestion, for example, must be more like individual cells ingesting small - if not microscopic - organisms, or does it have a mouth and digestive tract?
Along these lines, I would venture other odd sea animals, like sponges, only have nerve bundles, too? Or, perhaps something even more primitive? - Jinx
If I remember correctly, the sponges don’t have any nervous system at all, nor any other specialized cells, for that matter. And all coelenterates (jellyfish, polyps, corals, anenonomes, and the like) have specialized cells (including a rudimentary nervous system), but nothing that could really be described as organs.
Note that this is all from AP Biology eight years ago: High school simplifications, faulty memory, and recent developments in biology may all lead to inaccuracies in this post.
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*Originally posted by Jinx *
OK, on that note…does it have any definitive structures we can call organs, or is it just a blob of various specialized cells, perhaps? Digestion, for example, must be more like individual cells ingesting small - if not microscopic - organisms, or does it have a mouth and digestive tract?
No, the Phylum that jellyfish belong to (along with sea anemones, corals, etc.), Cnidaria, is not considered to have true organs at all. They are at what is called a “tissue” grade of body organization - they have body tissues, composed of distinct kinds of cells, but these are not organized into organs composed of several different kinds of tissues. They have a digestive cavity, but it only has one entrance (and exit). There is some extracellular digestion in the cavity, but it is completed by the cells ingesting food particles.
Sponges lack nerves. They are even more primitive than jellyfish. They lack tissue - they are at what is known as a “cellular” grade
of organization. They have specialized cells for some functions, but these are not organized into tissues.
BTW, jellyfish are NOT fish…
At work we refer to them as jellies.