Carybdea rastoni are a variety of smaller Box jellyfish with four tentacles, and which range in the Pacific Oceans from Japan to Hawaii. In the places where they are found, the jellies can be seen in pretty large smacks. Carybdea rastoni are very proliferate and can actually be invasive. Their sting is painful, but not lethal. I don't plan on handling these with my bare hands like I do with see nettles!
The polyps of carybdea rastoni are a little surprising. From research, I understood that they were small, but I was surprised at just how small these polyps really were. They are better viewed under slight magnification. I would say each polyp is about the size of a newly hatched Brine Shrimp. Interestingly, these polyps can open their mouths extremely large, and shove a whole baby brine shrimp inside! For that very reason, I am simply feeding them Brine Shrimp for now.
I haven't gotten any good pictures of these polyps because they are so small! Here is one off the web, from Jellyclub.
A few juvenile medusa came with the polyps. They were very interesting to look at. At around just a few mm they have the beginnings of 4 tentacles. As the pulse around erratically, they kinda become cute... in a dangerous way. One of the reasons you don't see these guys on display is because they are very hard to culture. It isn't entirely clear as to what they eat in their earlier stages. The Two Ocean Aquarium in South Africa has managed to raise wild juveniles up to adults on public display. They feed live Mysids to them. That appears to work really well. Unfortunately, the juveniles are far too small to eat them. They need some other food to feed on. I'm going to try feeding Rotifers to them, as brine shrimp seem too big to deliver much nutrition. I ordered a live rotifer kit (we will see how this goes) and I will start culturing Rotifers.
I also want to experiment with making a gelatinous food for them, and other jellies. Apparently agar and gelatin have been used to feed jellyfish before. Perhaps I can create a very nutrient dense gel for jellies.
Sorry, but these polyps and jellies will not be for sale or trade. I know they aren't lethal, but they are dangerous and also very invasive. If a public aquarium or research institute of some sort wants these, something could be arranged.
I'm going jellyfish collecting this Thursday. I'm hoping to find some more Sea Nettles (both of mine are male) and possibly some Chiropsalmus box jellies and Cannonballs.