The key difference between Cnidaria and Ctenophora is that the cnidaria show alteration of generation between medusa and polyp, while Ctenophora does not show alteration of generation; only medusa form is present.
Phylum Coelenterata is a subdivision of Kingdom Animalia. It consists of two main phyla Cnidaria and Ctenophora and approximately 15000 species included. They are invertebrates and mostly marine organisms. There are freshwater species as well. They have a simple tissue organization with two layers of cells, and they do not have a coelom. They reproduce mainly by asexual reproduction; by budding. Phylum Cnidaria includes coral animals, true jellies, sea anemones, sea pens, and their allies while phylum Ctenophora includes mainly comb jellies.
CONTENTS
1. Overview and Key Difference
2. What is Cnidaria
3. What is Ctenophora
4. Similarities Between Cnidaria and Ctenophora
5. Side by Side Comparison – Cnidaria vs Ctenophora in Tabular Form
6. Summary
What is Cnidaria?
Cnidaria is a phylum of animals and contains amazingly beautiful coral reefs, electrifying jellyfish, and many other interesting oceanic creatures. There are about 10,000 species belong to the phylum Cnidaria. These cnidarians are unique since they possess cnidocytes, which are not present in any of the other organisms. And, due to the presence of the cnidocytes, they all are unique among all other organisms. Furthermore, their outermost body layer is known as the mesoglea, which is a gel-like substance stacked between two epithelia that are single-cell layered. Also, the hydrostatic pressure maintains the shape of the body of cnidarians. However, some species have endoskeletons or calcified exoskeletons.
Moreover, they don’t usually have muscles. But, some anthozoans have muscles. The movements of the body are performed using the moving of fibres in the epithelium. Also, 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.
Figure 01: Cnidaria
Besides, the nerve net of the cnidarians is the nervous system, and it secretes hormones, as well. It is important to notice that their digestive system is incomplete. Also, one of the important characteristics 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.
What is Ctenophora?
Ctenophora is a phylum of Coelenterata. They are highly distinctive among all the animals due to the presence of the comb plates. Ctenophores have been recorded only from the ocean and never from the freshwater habitats. Also, 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 mm and 1.5 m long respectively. Furthermore, the presence of prey capturing sticky cells known as colloblasts is unique for the ctenophores.
Figure 02: Comb Jelly
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 are the Similarities Between Cnidaria and Ctenophora?
- Cnidaria and Ctenophora are two phyla of Coelenterata.
- Both are aquatic organisms.
- And they both are invertebrates.
- Also, both belong to the kingdom Animalia.
- Furthermore, the Cnidaria and Ctenophora have a simple tissue level organization.
- Also, no coelom is present in both groups.
- Moreover, they both have radial symmetry.
What is the Difference Between Cnidaria and Ctenophora?
The fundamental difference between Cnidaria and Ctenophora is that the cnidaria have distinguishing cnidocytes while the Ctenophora have distinguishing comb plate. Also, their habitat contributes to another difference between Cnidaria and Ctenophora. That is, Cnidarians live in both marine and freshwater while Ctenophora are totally marine organisms. Furthermore, a significant difference between Cnidaria and Ctenophora is that the Cnidarians are radially symmetrical while the Ctenophora are bi-radially symmetrical.
Moreover, one other difference between Cnidaria and Ctenophora is the diversity. Cnidarians are more diverse including 10000 species while Ctenophora are less diverse including only 150 species. Apart from that, cnidaria show alteration in a generation while Ctenophora do not show alteration in a generation. This is the key difference between Cnidaria and Ctenophora.
Summary – Cnidaria vs Ctenophora
Coelenterata has two subphyla namely cnidaria and Ctenophora. They are aquatic organisms. Cnidaria is a highly diverse group, which is a distinguishing feature called cnidocytes. Ctenophora is a less diverse group, which has comb plates. Furthermore, they are mostly biradially symmetrical. Also, Cnidarians live in marine and freshwater habitats while Ctenophora lives only in marine water. This is the difference between Cnidaria and Ctenophora.
Reference:
1.“Phyla Cnidaria and Ctenophora.” An Overview of Biodiversity, 17 Sept. 2018. Available here
2.“Cnidaria.” Wikipedia, Wikimedia Foundation, 25 Sept. 2018. Available here
Image Courtesy:
1.”599472″ (CC0) via Max Pixel
2.”Comb jelly”By Orin Zebest (CC BY 2.0) via Commons Wikimedia