Amoeboid cells produce the skeletal elements known as spicules. Some sponges have spicules that are made of flexible protein called spongin. From this type of sponge, bath sponges are produced. Reproduction in sponges is either sexual or asexual. Sometimes planktonic sperm is filtered in creating sexual reproduction.
Sponges are marine creatures that can be found in almost all habitats including polar regions.
There are also several freshwater sponges. Algae is often is symbiosis with sponges which is the reason many sponges are green. Phylum Cnidaria Cnidarians include the jellyfish, hydras, corals, and sea anemones. They have radial symmetric and tissues but no organs. The name cnidarian comes from the stinging cells called cnidocysts that every cnidarian has.