I've been able to setup several jellyfish aquariums in new classrooms in my school. This one is going in to my school's art room.
The art teacher, Mrs. Barber asked for some information about her new jellyfish. This is my quick response but if any R2R members want to chime in I'll make sure it gets to Mrs. Barber and her students. And feel free to correct me if I got anything wrong.
Q: What kind of jellyfish are they?
A: The jellyfish in the aquariums are moon jellyfish. They live in both the pacific and atlantic ocean and grow to be about the size of a dinner plate. They're one of the most commonly kept jellyfish because they're easiest to culture and feed. FYI many people 'in the know' prefer the term sea jellies or jellies over jellyfish. Jellies are actually plankton (can't swim and move with the water column) and are much simpler organism than fish. Labeling them 'jellyfish' can cause misconceptions because they are very different from fish. I personally use the label jellies and jellyfish interchangeably.
Q: Can we touch them?
A: They can actually be touched though they're very delicate and it's something I don't usually let kids do. They are mostly made of water and tear easily. They are so delicate that air bubble's trapped underneath their bell can actually rise through their tissue, poking holes in them. Even strong jets of water can injure them. Moon jellies have very small stinging tentacles around the edge of their bell that you can see if you look closely. It's actually these tentacles that trap most of the food they eat. Some jellyfish have dangerous or deadly venom but our moon jellyfish have no venom because the venom is produced by the foods they eat and they can't get the chemicals they need when they live out of the ocean. Marine biologist actually don't know what helps them produce the venom.
Q: How do they eat? Do they use their tenticles?
A: The 3 or 4 long tentacles are called oral arms. There's ciliated cells (cells with little flapping arms) that push food up them into the jellyfish's mouth. The jellyfish is a very simple animal, even more simple than an insect. In relation to other ocean animals, it's more like a plant than an animal though they don't photosynthesize. Jellies have a very basic orifice (like coral) that is an entrance and exit for food. They have a stomach inside the bell where food breaks down and then the food moves through a basic circulatory system (like blood vessels) to the cells. When we feed the jellyfish you can see the food in the stomach. FYI horseshoe shaped organs in the middle of the bell are actually the reproductive organs, not the stomach.
Q: What do they eat?
A: Jellyfish eat all kinds of things and the shape of their body actually influences what kind of food they can catch or eat. We feed our jellies live brine shrimp larva called artemia. When we feed them you can actually see the artemia swimming around the tank before the jellies catch them. Moon jellies can only eat very small types of plankton.
Q: Can they see or hear?
A: The jellies actually have very basic eyes on the edges of their bell. The eyes are little white spots in divots around the bell. They so are basic they can only sense light or dark and are mainly used to orientate the jellyfish and help it know when it's day or night. The jellies don't have brains and don't react to what they see. They don't have ears. Hearing and interpreting sound is a more complex function and requires a brain and more advanced organs. Animals like fish and whales can hear.
Q: Do they have a brain?
A: No. They don't need brains because their bodies and biological functioning are so simple. Many animals actually do better without brains (sometimes I wish I didn't have one
). The jellies don't really make decisions, they just flap around and eat. FYI they can't actually swim, the movement of their bells, called belling is more about collecting food than locomotion.
Q: What are the white balls in the aquarium? Students are convinced they're jellyfish eggs.
A: The little balls are filter media. The aquarium water is cleaned by bacteria that eat waste from the jellyfish and uneaten food. The bacteria live on the filter balls and crushed coral under that white plate. There are actually a number of invertebrates that live in the filter media including worms, copepods and shrimp that you can see if you look closely. They also help keep the tank clean. Adult jellyfish actually have a gender and the females do release eggs but they'd be microscopic.
