Have you ever snorkelled in the deep sea and noticed a lightning transparent animal resembling a jellyfish and reflecting a beautiful rainbow-like effect? Though Ctenophores look like Jellyfish, they do not belong to Phylum Cnidaria. These organisms belong to Phylum Ctenophora. This Phylum is not as familiar as other species of the animal kingdom. 

Ctenophores are-swimming, translucent, jelly-like, soft-bodied marine organisms with biradial symmetry and comb-like ciliary plates for movement. They lack nematocytes. They’re also referred to as sea walnuts or comb jellies. Members of this Phylum are entirely marine animals and are present on the surface of the ocean or the bottom of the sea. They are also known as Comb Jellies. This article will clarify the unknown facts about Phylum Ctenophora.

Phylum Ctenophora Definition

Phylum Ctenophora is also known as Comb jellies. This Phylum consists of bi-radially (radial + bilateral) symmetrical marine water invertebrates; they are mostly transparent and colourful organisms. The species of this Phylum mainly belong to aquatic habitat, and they do not live in freshwater. This Phylum includes animals like Sea Walnut, Sea Gooseberries, Venus girdle, etc. 

The term Ctenophora was coined by Georges Cuvier. The name of this Phylum originated from the Greek word ” Ctene”, which means “comb,” and ” Phora” means “bearer”, which indicates the ciliary combs like structure over the organism’s surface. 

Fig: Example of Ctenophora

History of Phylum Ctenophora

According to the found fossil in Lagerstatten as far back as the early Cambrian, the origin of Ctenophora is \(515\) million years ago. The Ctenophores were first recognized in \(1671\) by Linnaeus, who placed Ctenophores under the group zoophyte. In \(1829,\), Eschscholtz was the first zoologist to recognize the Phylum Ctenophora. Since then, many zoologists and scientists have included Ctenophores under Phylum Coelenterata. But in \(1889,\) zoologist Hatschek has separated Ctenophora as an entirely different Phylum. There are about \(150\) species in this Phylum.

Fig: Fossil of Ctenophora (Comb Jelly)

Characteristics of Phylum Ctenophora

1. Habitat: These are exclusively marine animals. 
2. Habit: Animals of this Phylum are solitary and swimming.
3. Body Organization: They are diploblastic acoelomate organisms. The body is transparent, gelatinous, soft and without segmentation, along with a pair of long, solid, retractile tentacles.
4. Body Symmetry: These organisms are bi-radially symmetrical.
5. Tissue: In these invertebrates, a tissue-level organization is present.
6. Locomotion: They have eight strips of cilia, called comb rows. These comb-like rows help in locomotion. 
7. Reproduction: They are hermaphrodite animals, and reproduction occurs through sexual means.
8. Fertilization: These organisms have external fertilization and indirect development.
9. Digestive system: They have both extracellular and intracellular digestive systems.
10. Nervous system: They have an aboral sense organ called the statocyst for balance.
11. Respiration and excretion: They do not have specific organs for respiration and excretion, and generally, the body surface does this process.
12. Size and Shape: The size of the tiny Phylum Ctenophora (\(0.04\) inch) spheroids to long (\(4.9\) feet) ribbons. The Ctenophora are lobe-shaped.
13. Example: Pleurobrachia, Ctenoplana, etc.

Phylum Ctenophora Classification

The Phylum Ctenophora is divided into two classes which are mentioned below:

Tentaculata
a) They have two tentacles that can retract into specialized sheaths and small stomodaeum.
b) Sea walnuts have a large mouth and mainly feed on larval molluscs and copepods.
c)  Venus girdle is a flattened, ribbonlike Ctenophora found in tropical waters.
d) In sea gooseberries, the tentacles are smaller secondary, and the primary tentacles are reduced; there are smaller, secondary tentacles, and the primary tentacles are reduced. These organisms are commonly found on the Atlantic and Pacific coasts.
e) Examples: Sea Walnut, Sea gooseberry, Venus Girdle etc.

Nuda
a) The species of this class do not have tentacles.
b) They have a largemouth, and they feed on Jellyfish and other ctenophores.
c) They are swimmers and are typically found in all oceans and seas around the world.
d) Examples: Beroe, Mnepmiopsis, etc.

Fig: Classification of Ctenophora

Phylum Ctenophora Examples

The examples of Phylum Ctenophora are mentioned below:

Pleurobrachia (Sea Walnut)

1. The systematic position of Pleurobrachia is –

Kingdom: Animalia
Phylum: Ctenophora
Class: Tentaculata
Order: Cydippida
Family: Pleurobrachiidae
Genus: Pleurobrachia

2. They have two tentacles.
3. They have a transparent body, pear or walnut-shaped.
4. Their mouth is situated at the centre of the oral pole.
5. The sense organs are present at the aboral pole.
6. Statocyst is a modified sense organ that acts as an organ of equilibrium.
7. These are marine animals present all over the world.

Fig: Pleurobrachia

Beroe

1. The systematic position of Beroe is –
Kingdom: Animalia
Phylum: Ctenophora
Class: Nuda
Order: Beroida
Family: Beroidae
Genus: Beroe
2. These are commonly known as the swimming eye of the cat.
3. Their body is thimble-shaped and laterally compressed along the oral and aboral end.
4. Tentacles are absent, and the mouth is wide opening leading into the stomodaeum (Pharynx).
5. Development takes place through cydippid larva.

Fig: Beroe

Cestum Veneris (Venus Girdle)

1. The systematic position of Jellyfishis –
Kingdom: Animalia
Phylum: Ctenophora
Class: Tentaculata
Order: Cestida
Family: Cestidae
Genus: Cestum
2. Venus Girdle are transparent and ribbon-shaped.
3. The comb rows are present on one side of the ribbon, and the other side is the mouth.
4. Venus Girdle are found on the surface water of the sea.
5. Venus Girdle feeds on crustaceans and molluscs.

Fig: Cestum Veneris (Venus Girdle)

Importance of Phylum Ctenophora

The economic and ecological importance of Phylum Ctenophora are mentioned below:
Economic Importance
1. They make beautiful sights while diving and snorkelling.
2. One benefit of Ctenophora lay in their genetics. The luminescence instantly produced by Ctenophores is used as a “biomarker” or “biotag.”
3. They are used in research by scientists to identify activation genes by creating different glowing cats, mice, and other animals and indicating whether the changes made to these animals’ genetics are working.

Ecological Importance
1. They reproduce quickly and are good predators, so they control the plankton population underwater.
2. They can starve and shrink at the time of scarcity of food, and they can adapt to increased temperatures that give them an advantage in changing environmental conditions.

Interesting Facts

a. Cestum veneris (“Venus’ girdle”) is the largest Ctenophores that stretch up to \(1.5\,{\rm{m}}\left( {4.9{\rm{ ft}}} \right)\) long.
b. Minictena luteola, with a length of \(0.06\) inches, is the smallest Ctenophore.

Summary

Animals in Phylum Ctenophora are typically marine, and they do not live in freshwater. They are mainly present on the ocean surface or in oceans’ deep water. Organisms of this species are bi-radial symmetrical. The animals of this Phylum are not so familiar to humans.
It is a small group of about \(150\) species, and the examples of the animals found in this Phylum are Sea Walnut, Sea gooseberry, Venus Girdle etc. Ctenophores reproduce quickly and are good predators, so they control the plankton population underwater

FAQs

Q.1. What organisms are present in the Phylum Ctenophora?
Ans: The organisms present in the Phylum Ctenophora are Sea Walnut, Beroe, Venus Girdle, etc.

Q.2. What are the different classes of the Phylum Ctenophora?
Ans: The different classes of Phylum Ctenophora are Tentaculata and Nuda.

Q.3. What is the meaning of the term Ctenophora?
Ans: The name of Phylum Ctenophora originated from the Greek word its name Ctene, which means “comb,” and Phora means “bearer” which indicates the ciliary combs like structure over the surface of the animal.

Q.4. What are the characteristics of Phylum Ctenophora?
Ans: The characteristics of Phylum Ctenophora are:
a. They are diploblastic acoelomate organisms. The body is transparent, gelatinous, soft and without segmentation, along with a pair of long, solid, retractile tentacles.
b. These organisms are bi-radially symmetrical organisms.
c. In these invertebrates, tissue-level organization is present.
d. They have eight strips of cilia, called comb rows. These comb-like rows help in locomotion. 
e. They are hermaphrodite animals, and reproduction takes place through sexual means.

Q.5: How many ciliated rows are present in Comb jellies?
Ans: There are eight ciliated rows present in Comb jellies.

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