Brief Cnidaria Introduction
Cnidaria are very diverse, and can be shown because of the existence of colonial siphonophores, massive corals and medusae(jelly fish), feathery hydroids, and box jellies that have complicated eyes. They are vast in varieties and are armed with stinging cells called Nematocysts. They are united based on the presumption that their nematocysts have inherited from a common ancestor.
Cnidaria Phylum
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 posion 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 medusa stage (inverted disk like shape). The polyp stage is a sessile form, and the medusa 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 medusa stage (inverted disk like shape). The polyp stage is a sessile form, and the medusa 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.
Sea Anemone (Anthozoa)
A Sea Anemone is from the Anthozoa group, that is named after the Anemone which is a earthy flower. Their polyp stage is larger in this case for a better digestive track for larger preys but they lack the medusa part. Since they are all in the Cnidarian Anthoza group they are closely related by system of structure and physical characteristics with jelly fish, corals and hydra. They are put into this group because of the polyp structure as well as the poison that is located in the center disk at the bottom of the structure.
Box Jelly Fish (Cubozoa group of Cnidarian)
These box jellyfishes are like regular jellyfishes except that they can maneuver around the water faster, and their sight is pretty well because they do not have a brain. Box Jellys follow their name and are physically like other jellyfishes except their head are squared shaped when viewed from the top. With the physical features of the tentacles, head shaped, polyp parts they show the muscular skeletal system that the phylum has.
Hydra from the Hydrozoa group
Hydra is one of the most known species from the Hydrozoa group. This group is one of the diverse and it also stays in the Polyp stage its entire life without moving to the Medusoid(Medusa). These hydrozoans are collectible and they are located in a colony. These can be found in most unpolluted water that is fresh such as ponds, lakes, streams that are in temperate and tropical regions. They can be found by gently sweeping a net through weedy areas. The hydra does not have a true brain/muscle cell in their body.