As you know, I am in desperate need of extra credit. I have another answer for you, Mr. Catron.
I believe that the picture from April 18th is a jelly fish and it belongs to the class Scyphozoa and phylum Cnidaria. This is what I have found out about the nematocysts. The stinging structure varies according to species, but generally consists of a hollow coiled thread with barbs lining its surface. Nematocysts are concentrated on the tentacles or oral arms of a jelly fish. A single tentacle can have hundreds or thousands of nematocysts embedded in the epidermis. Triggers of nematocysts are activated when contact is made with another object. Pressure within the nematocyst forces the stinging thread to rapidly uncoil. The thousands of nematocysts act as small harpoons, firing into prey, and injecting paralyzing toxins. Stings usually paralyze or kill only small creatures, but some jellyfish are harmful to humans.
Emily Harris, Billings West High School