Cnidaria Phylum comes from Cnidos or Knidos, a Greek word that means stinging nettle. Most Cnidarians contain nematocysts, a portion of their body that ejected threads that are tipped with poison to protect itself. Many thousands of cnidarian species live all over the world's ocean, from the tropics to both north and south poles. Some live on the surface and some live on the bottom, however fewer number of species are found in running rivers and fresh, clean lakes.
There are 4 basic groups inside the Cnidaria Phylum. The four major groups are:
1. Anthozoa, this group includes anemones, true corals, and sea pens that are from the Precambrian age, 2. Cubozoa, this group contains the amazing box jellies with complicated eyes and powerful toxins to protect itself, 3. Hydrozoa, this is the most diverse group that contains fire corals, hydroids, siphonophores, and many medusae, as well as 4. Scyphozoa, the true jellyfish.
Cnidarian's physical system consists of two basic body forms. The cylinder, tentacled shaped polyp stage and the medusae stage (inverted disk like shape). The polyp stage is a sessile form, and the medusae stage is a free-swimming form. These structures consists of two layers, the epidermis (outer skin layer), and the gastrodermis (inner layer). The difference between these two layers is the fact that a gel like substance called mesoglea is present. Sometimes the mesoglea contains cells and sometimes connective tissue.
There are 4 basic groups inside the Cnidaria Phylum. The four major groups are:
1. Anthozoa, this group includes anemones, true corals, and sea pens that are from the Precambrian age, 2. Cubozoa, this group contains the amazing box jellies with complicated eyes and powerful toxins to protect itself, 3. Hydrozoa, this is the most diverse group that contains fire corals, hydroids, siphonophores, and many medusae, as well as 4. Scyphozoa, the true jellyfish.
Cnidarian's physical system consists of two basic body forms. The cylinder, tentacled shaped polyp stage and the medusae stage (inverted disk like shape). The polyp stage is a sessile form, and the medusae stage is a free-swimming form. These structures consists of two layers, the epidermis (outer skin layer), and the gastrodermis (inner layer). The difference between these two layers is the fact that a gel like substance called mesoglea is present. Sometimes the mesoglea contains cells and sometimes connective tissue.