Difference Between Cnidaria and Ctenophora

Cnidaria vs Ctenophora
 

Cnidaria and Ctenophora are two different invertebrate phyla with interesting features. Since the animals included in both these phyla were formerly classified in the Phylum: Coelenterata, it could be confusing for some. However, there are many exhibited differences between cnidarians and ctenophores, but the most interesting distinctions are discussed in this article. However, one of the differences that would not be reflected in a biologically based account such as the familiarity to people; cnidarians are more commonly known to general people than the ctenophorans are.

Cnidaria

Cnidaria is a phylum of animals, which contains amazingly beautiful coral reefs, electrifying jellyfish, and many other interesting oceanic creatures. There are about 10,000 species of cnidarians and all of them are unique among all other organisms for the presence of the Cnidocytes. Their outermost body layer is known as the mesoglea, which is a gel-like substance stacked between two single-cell layered epithelia. The shape of the body of cnidarians is maintained via hydrostatic pressure, but some species have endoskeletons or calcified exoskeletons. They don’t usually have muscles, but some anthozoans do. The movements of the body are performed using the moving of fibres in the epithelium. Cnidarians do not have systems for respiration and circulation, but the cellular diffusion of contents takes place according to osmotic pressure gradients inside their bodies. The nerve net is the nervous system, and it secretes hormones, as well. It is important to notice that their digestive system is incomplete. One of the important characteristic of them is the alteration of generations with two body forms, and those are the sexual body plan (medusa) and the asexual body plan (polyp). However, the overall body plan of all the cnidarians is always radially symmetrical. The medusae are usually free-swimming animals, while polyps are sessile.

Ctenophora

Ctenophores are simply the members of the Phylum: Ctenophora and they are highly distinctive among all the animals for the presence of the comb plates. Ctenophores have been recorded only from the ocean and never from the freshwater habitats. This is not a highly diversified group of invertebrates, and there are only about 150 identified species. However, the size difference is extraordinary compared to the number of species, as the smallest and the largest members are about 1 millimetre and 1.5 metres long respectively. The presence of prey capturing sticky cells known as colloblasts is unique for the ctenophores. The body plan of these animals is radially or biradially symmetrical, but only the medusa form is present among them. It would be important to notice that the bioluminescence is very common among ctenophores. Their nervous system consists of a nerve net, but they lack body organ systems such as respiratory and circulatory systems. However, the digestive system is complete, and there is an oral-aboral axis of the body.

 

What is the difference between Cnidaria and Ctenophora?

• Cnidarians are highly diversified in terms of the number of species compared to ctenophores.

• The body size range is higher among ctenophores than in cnidarians.

• The majority of cnidarians live in the ocean while a very little number of species could be found in freshwater, whereas all the ctenophores have been recorded only from the saltwater environments.

• Cnidarians are radially symmetrical while ctenophores are either radial or biradial in their body symmetry.

• The alteration of generations is present among cnidarians but not in ctenophores.

• Cnidarians have Cnidocytes to disable the prey while ctenophores have colloblasts to capture prey.

• Bioluminescence is more common among ctenophores than in cnidarians.

• Digestive tract is complete in ctenophores but not in cnidarians.

• Ctenophores have a comb plate but never in cnidarians.