As you read this, you probably must be wondering if this is another group of animals that you know nothing much about. But, if you have seen the movie, Finding Nemo, you most certainly have seen a sea anemone on screen! A sea anemone is a member of Phylum Coelenterata. It has a symbiotic relationship with the clownfish. Some of the other animals that belong to this phylum include coral animals, true jellies, sea pens, comb jellies, hydra, etc. Let us learn about these fascinating creatures.
These are typically invertebrate animals, which show a very simple level tissue organisation. They are aquatic animals and are mostly found in marine environments, attached to the rocks at the bottom of the ocean. A few species are also found in freshwater habitats. Coelenterates can be found solitarily or in colonies. You can find them sedentary or free swimming.
Coelenterates can be called as the simplest animal group that has true tissues and have the characteristic coelenteron or the gastrovascular cavity.
Characteristic Features of Phylum Coelenterata
- They are multicellular organisms, exhibiting tissue grade of the organisation.
- They are diploblastic, with two layers of cells, an outer layer called the ectoderm and the inner layer called the endoderm. There is a non-cellular layer that is the mesoglea in between the ectoderm and the endoderm.
- They show radial symmetry.
- They have a single opening in the body through which food is taken in and also waste is expelled out.
- The opening in the body is surrounded by tentacles.
- Digestion takes place in the body cavity which is the coelenteron.
- They can live in marine or freshwater habitats.
- They can be solitary or live in colonies. Each individual is a zooid.
- These organisms show two morphological forms – Polyps and Medusa.
- Polyps contain exoskeleton and endoskeleton.
- The skeletons are composed of calcium carbonate.
- Most if the coelenterates are carnivorous in nature with a few exceptions such as the s corals. They get their food from other animals that live symbiotically within them.
- Digestion is both intracellular and extracellular.
- Tentacles have special structures known as the nematocysts which help in capturing and paralyzing prey. Coelenterates simply wave their tentacles and when a prey comes in contact, the nematocysts inject the toxin that paralyses or kills the prey. Nematocysts are the most distinguishing feature of this phylum.
- Coelenterates do not have sensory organs.
- Respiration and excretion occur through simple diffusion.
- The circulatory system is absent.
- Asexual reproduction is seen in polyps, through budding and sexual reproduction is seen in medusa form, through gametic
Classification of Phylum Coelenterata
This phylum is further divides into three classes:
- Aurelia ( Jelly Fish)
- Adamsia (Sea Anemone)
Learn more about Phylum Echinodermata here in detail.
Solved Questions For You
Q: In which phylum, do organisms have nematocysts. Explain their significance.
Ans: Nematocysts are found in the organisms belonging to Phylum Coelenterata. They are, microscopic stinging structures that are present in the tentacles. Their primary use is to capture and paralyze prey such as fishes and marine animals.
Q: Are coelenterates diploblastic or triploblastic?
Ans: Coelenterates have two layers of cells, ectoderm and endoderm. Hence they are diploblastic.