Sponges composed of organic (shredding) fibers have been used by humans for thousands of years for cleaning and other purposes. Sponge diving has declined significantly due to overfishing and most sponges these days are synthetic.
Cnidarians
The Phylum Cnidaria ("Ny-DARE-eeya") consists of about 10,000 species of "simple" animals found only in marine habitats and includes Class Anthozoa (corals and sea anemones), Class Hydrozoa (hydrozoans), Medusozoa Subphyla: Class Cubozoa (box jellies), Staurozoa which contains the Order Stauromedusae (stalk jellies). The phylum Cnidaria may hong kong email list also contain the Family Polypodiidae and the Family Tetraplatidae. Cnidarian species have special stinging cells called cnidocytes (see figure). Cnidarians evolved during the Precambrian Era and are some of the earliest known multicellular life forms.
Most cnidarians have a very basic body plan that includes a digestive cavity with one opening. This opening functions as the mouth and anus for the organism. The only true organs in cnidarians are the gonads. Most cnidarians are symmetrical, an observation known as “radial symmetry.” Cnidarians also have an ectoderm (tissue that covers the outer surfaces of the body) and an endoderm (inner layer of cells that form the gastrointestinal and respiratory tracts, and internal organs). The ectoderm is connected to the endoderm by a gel-like substance known as mesoglea. Cnidarians use a very basic nerve network and receptors to get impulses moving. Oxygen is absorbed directly from water through the tissues.
