Jellyfish Phylum

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Jellyfish belong the phylum "Cnidaria" which is part of the kingdom "Animalia". Apart from the jellyfish, other species that belong to this phylum include corals, sea anemones, hydras, sea pansies, sea fans and sea whips. The word 'Cnidaria' is derived from the Greek word "cnidos", which means stinging nettle. The term Cnidaria also refers to to Cnidocysts. These are the specialised cells which contain nematocysts, which are the stinging organelles that allow the Cnidaria to subdue their prey or protect themselves from predators.

In recent times, the name Cnidaria has replaced the use of an older term of Coelenterata. This term is now often applied to both the Cnidaria and the Ctenophora together, based on the fact that species belonging to these two phyla have radial or biradial symmetry.

Some of the other common characteristics of the Cnidaria phylum include:

All species belonging to this phylum have bodies that have radial symmetry. This means that they are the same shape from every side and that the whole body is around a central axis.
Most species in this phylum have bodies that are multi cellular and that have very few tissues. At most, there are some very rudimentary organs present.
The bodies of the species belonging to the phylum have a mouth as well as a small internal digestive cavity, mainly consisting of the gullet, the stomach and the intestines.
One of the more interesting characteristics of the species of this phylum is the fact that they exist in two different body forms. They are a polyp or a medusa at different times in their life cycle.
The reproductive cycle of the members of this phylum is also distinctive. It may be sexual, asexual or both.
Most members of the Cnidaria phylum have a strong nervous system. Without the presence of a brain, the central nervous system is responsible for the organism's reaction to stimuli.
The members of the Cnidaria phylum all undergo a distinctive planktonic stage when they are larvae.
Most members of the Cnidaria phylum live in marine habitats, but some including jellyfish, are known to live in freshwater habitats.
The members of the Cnidaria phylum are divided into two distinct categories based on their eating habits- they are either carnivorous or they are filter feeders.

The phylum Cnidaria is divided into four main categories or sub groups. They are:

Anthozoa: This groups mainly contains sea anemones and corals.

Cubozoa: Jellyfish that are known for the potency of their venom, like the box jellyfish, belong to this group.

Hydrozoa: This group contains many different types of medusa as well as fire corals, siphonophores, etc.

Scyphozoa: This is the group that most jellyfish belong to.

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