Cnidarians Background Information

Cnidarians: Introduction and Important Classes.

Cnidarians are a phylum are simple animals in the kingdom Animalia, with more than 9,000 species. These almost 10,000 species are sorted into 4 different classes: Anthozoa, Hydrozoa, Cubozoa, and Scyphozoa. Each of these classes of cnidarians has their own unique characteristics. 

The Classes: 

Anthozoa –

This class includes coral, sea anemones, and sea pens. This is the most diverse group of cnidarians, containing around 6,500 species. The life cycle for this group is different than that of the other 3 classes, as there is a very reduced medusa stage, and in some species, this phase is more present at all.

Hydrozoa –  

This class includes hydroids, siphonophores, fire corals. All of these animals tend to very small, but often reside in colonies. These colonies can become very large, and the entire colony will express only one gender - either male or female. 

Cubozoa - 

This class includes jelly fish like animals called box jellies and sea wasps. Box jellies are called such, as they have a cube shaped medusa stage. It is this class of cnidarians which are the most lethal; their venom can cause paralysis and even death of humans and other large animals. These jellies are so unique because they have true eyes! (See below?!)

Scyphozoa - 

This class includes the true jellies. All of these jellies can be found only in marine environments. Species of jellyfish in this calls have been recorded as being more than 6.6 feet in length!