Jellyfish - More CnidariansWe'll start by explaining that anemone, coral and jellyfish are all related. We broke them up into two different sections because of their body types. They are all from the phylum Cnidaria. Comb jellies are a side step away from jellyfish. They are in the phylum Ctenophora. They look similar, but are different in some important ways.
we discussed the basic ideas of Cnidarians when we talked about anemone and coral. Jellyfish are different in that they are not anchored to anything. Where jellyfish and coral are considered polyp shapes, jellyfish are in a medusa shape. Medusas are free swimming shapes that have their tentacles on the bottom of their body (not facing up like anemone). Since they move around, that newly evolved nervous system comes in handy.
The main body of a jellyfish is called the bell. That bell moves through a coordinated contraction that forces water out and thrusts the jellyfish forward. They spend their whole life cycle floating with the currents and capturing prey in their tentacles. They also have those stinging cells (nematocysts) on the tentacles to paralyze fish and then eat them.
Comb JelliesComb jellies are not true jelly fish, they are kind of one step up. The big differences...
- Comb jellies use cilia flapping on their sides to move. They do not contract a bell like jellyfish.
- Comb jellies use cells called colloblasts to capture their prey. These cells stick to the prey, not harpoon them.
- They have two (2) holes. While true jellies have a sealed bell with only one opening (like the one opening of an anemone), comb jellies have a small opening at the top of their body and one at the bottom so that water can flow through them.
- They often have plates for protection on the outside of their bodies. The plates help comb jellies maintain their shape. Since they don't move by contracting their whole body, it helps keep them a little more streamline.
Pacific Sea Nettles (National Aquarium Video)