Ctenophore: Definition, Classification, Types, Characteristics, Adaptations

Edited By Irshad Anwar | Updated on Jul 02, 2025 06:02 PM IST

Ctenophora is a simple, soft-bodied phylum of marine animals also known as sea walnuts or comb jellies. They are known for their beautiful, glass-like bodies that usually emit light at night due to their bioluminescence. Ctenophores propel themselves in water with eight rows of tiny hair-like appendages called ctenes or comb plates. To date, researchers have found about 100 species of ctenophores, and all of them live in salty oceans and seas.

This Story also Contains

Definition Of Ctenophora
Taxonomy And Classification of Ctenophora
Morphology And Anatomy of Ctenophora
Physiology and Behaviour of Ctenophores
Habitat And Distribution Of Ctenophora
Ecological Role Of Ctenophora
Recommended Video on Ctenophores

Ctenophore: Definition, Classification, Types, Characteristics, Adaptations

These animals have a two-layered body (diploblastic) and display radial symmetry, i.e., they have body parts disposed on a central axis. They do not have stinging cells but use sticky cells called colloblasts to catch food. Ctenophores are usually small, but some of them reach a length of 1.5 meters. They are an important part of the marine food web as predators and prey.

Definition Of Ctenophora

Ctenophora is a class of marine animals that are small, soft, and jelly-like in structure. They are also known as comb jellies due to the eight rows of comb-like plates (ctenes) that they possess, which help them move through water. Ctenophores are diploblastic, i.e., their bodies consist of two layers of cells, and they exhibit radial symmetry. They exist only in saltwater and are characterised by their glowing bioluminescence.

Ctenophores have specific adhesive cells named colloblasts to trap prey.
Their body are clear and tend to glow in the dark.
They swim with the help of rows of minute cilia on comb plates.
Ctenophores lack stinging cells such as those in jellyfish.
They serve a key function in the ocean ecosystem as predators of small animals.

NEET Highest Scoring Chapters & Topics

Know Most Scoring Concepts in NEET 2024 Based on Previous Year Analysis.

Know More

Also Read

Taxonomy And Classification of Ctenophora

Ctenophora is a minor phylum of marine invertebrates, which are divided into groups according to the shape of their bodies, tentacle type, and absence or presence of features. They are the kingdom Animalia and split from cnidarians because they do not have stinging cells. Scientists have placed ctenophores into various classes and orders based on how they appear and move in water. Its purpose of explore is their diversity and function in the marine system.

Ctenophora is a phylum called Ctenophora within the kingdom Animalia.
They are further divided into two classes: Tentaculata and Nuda.
Class Tentaculata comprises species with tentacles.
Class Nuda comprises species without tentacles.
All ctenophores are marine and live in saltwater.
They are diploblastic animals and exhibit radial or biradial symmetry.
Ctenophores are classified under a distinct phylum because of their cilia and distinct body structure.
There are approximately 100 species of ctenophores discovered to date.

Morphology And Anatomy of Ctenophora

Ctenophora are jelly-like, soft, and marine animals whose bodies are transparent and can be oval, spherical, or ribbon-shaped. Their body has bilateral symmetry and consists of two layers (diploblastic) with a jelly-like mesoglea between them. They have eight rows of comb plates with cilia lining them that assist in swimming. They have two long tentacles carrying colloblasts for food capture by most species. Within, they have a basic digestive tube, a nerve net, and no skeleton or hard structures. All basics about the Morphology and Anatomy of Ctenophora are discussed below:

Feature	Description
Body shape	Soft, transparent, jelly-like, oval or spherical in form
Symmetry	Radial symmetry (body parts arranged around a central axis)
Body layers	Diploblastic (body made of two cell layers: ectoderm and endoderm)
Movement	Moves with 8 rows of ctenes (comb plates made of cilia)
Tentacles	2 long, retractable tentacles with colloblasts (sticky cells for catching prey)
Bioluminescence	Many species glow in the dark (produce light)
Digestive system	Complete gut with mouth and anal pore
Nervous system	Diffuse nerve net (no brain)
Skeleton	No skeleton; body supported by jelly-like mesoglea
Habitat	Exclusively marine (saltwater), mostly free-swimming

Physiology and Behaviour of Ctenophores

Ctenophores have a simple physiology appropriate to their life in oceanic waters. They glide effortlessly with the help of comb plates beating and capture food with colloblasts on their tentacles. Their body has bioluminescence, which helps them glow when it is dark. They have a simple nerve net for movement and touch response. Ctenophores are free-swimming predators which drift or glide while feeding on small animals such as plankton. Other important features are discussed below in the table:

Feature	Description
Feeding Mechanisms	Capture plankton and small crustaceans using colloblasts (sticky cells on tentacles). Tentacles are long and retractable, also they sweep through water to trap prey. Prey is carried to the mouth and into the digestive canal. The feeding method is different from cnidarians, which use nematocysts (stinging cells).
Reproduction	Simultaneous hermaphrodites (have both male and female sex organs). Reproduce sexually by releasing gametes into the water. Larva is called a cydippid , it develops slowly into adult form. Some species also reproduce asexually by fragmentation.
Locomotion	Swim using ciliary rows or comb plates that run along their body. Comb plates beat in a coordinated way to help smooth gliding. Allows for easy turns, prey capture, and predator escape.

Habitat And Distribution Of Ctenophora

Ctenophora inhabit of marine environments alone, existing in seas and oceans all over the world. They float freely close to the water surface most of the time, although species exist at deeper levels. Ctenophora exist in saltwater only, not found in freshwater. Ctenophores exist globally across tropical, temperate, as well as polar regions, indicating their capacity to adapt in various temperatures and climates. Some important points are discussed below:

Ctenophores are found in oceans worldwide, inhabiting almost all major marine environments from coastal waters to the open ocean, and pelagic to deep-sea settings.
Their geographic distribution somewhat mirrors that of the sea, existing in polar and tropical waters and varied depth zones, such as surface and deep-sea environments.
In these different marine environments, its presence explains its adaptability and ecological importance in global oceanic ecosystems.

Ecological Role Of Ctenophora

Ctenophora are key components of the marine ecosystem as active predators of plankton and small crustaceans. Feeding on these creatures, they control plankton populations and preserve the balance of the food chain. They are also prey for larger aquatic animals such as fish and turtles. In some areas, when their population grows very fast, ctenophores can influence fisheries by competing with juvenile fish for food. Some other important points are discussed below:

Ctenophores form an integral part of the marine food chain by preying on small marine animals like zooplankton, copepods, and even the larvae of fish, thereby controlling their populations.
They capture their prey with help from the colloblasts on their tentacles. In turn, they also become the prey for larger marine animals like fish and jellyfish.
Ctenophores are known to affect the population dynamics of marine species by preying on zooplankton and fish larvae.
This impact, as with other invasive species like Mnemiopsis leidyi, could result in the disruption of ecosystems like the Black Sea, causing a decline in local populations and fundamental changes in food web structures.
This need not be so if the population of ctenophores is monitored and managed to protect marine biodiversity.

Recommended Video on Ctenophores

Other useful Resources:

Ascaris male and female diagram	Bed bug life cycle
Animal Kingdom Concept Map	Bird life cycle
Bat scientific name	Birds skeletal system

Frequently Asked Questions (FAQs)

1. What are the key characteristics of Phylum Ctenophora?

They are jelly-like, radially symmetrical, marine invertebrates that locomote principally using ciliary plate combs and often bioluminescence.

2. How do ctenophores differ from jellyfish?

Unlike jellyfish, Ctenophora uses colloblasts for capturing prey instead of using nematocysts. They also have about eight rows of light-producing ciliary plates meant for locomotion.

3. What is the role of bioluminescence in ctenophores?

Bioluminescence in ctenophores may also be used in attracting prey for predation and in defence as a mechanism that could scare or confuse predators.

4. Where are ctenophores commonly found?

The ctenophores are found in abundance in oceans and seas the world over, ranging from surface waters to deep-sea environments and across wide geographic regions.

5. What is the ecological impact of ctenophores on marine environments?

Ctenophores affect the biodiversity of the sea by regulating zooplankton populations, and invasive species have been known to cause severe ecological perturbation.

6. What are ctenophores and why are they called "comb jellies"?

Ctenophores, also known as comb jellies, are marine animals characterized by eight rows of comb-like cilia used for swimming. They're called "comb jellies" because these rows of cilia resemble the teeth of a comb. Unlike true jellyfish, ctenophores lack stinging cells and are not part of the phylum Cnidaria.

7. What is the "ctenophore rosette" and what is its function?

The ctenophore rosette is a structure at the aboral (top) end of the animal: 1) It contains the statocyst for balance and orientation. 2) It coordinates the beating of cilia in the comb rows. 3) In some species, it may play a role in detecting light or chemical signals. The rosette is a key control center for ctenophore movement and behavior, demonstrating how these animals can perform complex functions without a centralized brain.

8. What is the ecological role of ctenophores in marine ecosystems?

Ctenophores play important roles in marine food webs: 1) They are voracious predators of small planktonic organisms, helping to control their populations. 2) They serve as food for various marine animals, including some fish and sea turtles. 3) In some areas, ctenophore blooms can significantly impact local ecosystems by consuming large amounts of zooplankton, potentially affecting fish larvae survival.

9. What is the "ctenophore invasion" and why is it a concern for some ecosystems?

The "ctenophore invasion" refers to the rapid spread of certain ctenophore species, particularly Mnemiopsis leidyi, in non-native habitats. This is concerning because: 1) These invasive ctenophores can consume large amounts of zooplankton, potentially disrupting local food webs. 2) They can outcompete native species for resources. 3) In some areas, like the Black Sea, ctenophore invasions have been linked to declines in commercial fish stocks, causing economic impacts.

10. What is the evolutionary significance of ctenophores?

Ctenophores are of great interest in evolutionary biology because: 1) They're one of the earliest-branching animal lineages, providing insights into early animal evolution. 2) Some studies suggest they may be the sister group to all other animals, even more basal than sponges. 3) Their unique combination of features (like a nervous system but no true muscles) challenges our understanding of how complex animal traits evolved.

11. How do ctenophores regenerate, and why is this ability significant?

Many ctenophores have remarkable regenerative abilities. They can regrow substantial portions of their body if damaged, including entire organ systems. This ability is significant because: 1) It helps them survive predator attacks. 2) It provides insights into the mechanisms of tissue regeneration, which could have implications for regenerative medicine. 3) It raises questions about the evolution of regenerative capabilities in animals.

12. What is the significance of bioluminescence in ctenophores?

Many ctenophores exhibit bioluminescence, producing light through chemical reactions. This ability serves multiple purposes: 1) It can act as a defense mechanism, startling predators. 2) It may help attract prey. 3) In some species, it might play a role in mating behaviors. The bioluminescence in ctenophores is often blue or green and can create spectacular light displays in the ocean.

13. What adaptations do deep-sea ctenophores have?

Deep-sea ctenophores have several adaptations: 1) Many are highly transparent or red in color, making them nearly invisible in the deep ocean. 2) Some have enlarged mouths to capture scarce prey more efficiently. 3) Their bioluminescence may be used for communication in the dark environment. 4) Many deep-sea species have reduced or modified comb rows, reflecting the different locomotion needs in deep water. These adaptations allow ctenophores to thrive in the challenging deep-sea environment.

14. How do ctenophores cope with changes in salinity?

Ctenophores have several adaptations to cope with salinity changes: 1) Many species can tolerate a range of salinities by adjusting their internal ion concentrations. 2) Some have specialized cells called porocytes that help regulate water and ion balance. 3) In low salinity environments, some ctenophores can increase their swimming speed to move to areas with more suitable conditions. These adaptations allow ctenophores to inhabit diverse marine environments, from estuaries to the open ocean.

15. How do ctenophores respond to environmental stimuli?

Despite lacking a centralized brain, ctenophores can respond to various stimuli: 1) They have sensory cells that can detect light, allowing some species to perform daily vertical migrations. 2) They can sense chemical cues in the water, which helps in finding food. 3) Many species can detect physical contact and respond by retracting tentacles or changing swimming direction. 4) Some ctenophores can even learn from experience, showing a surprising level of behavioral plasticity.

16. How do ctenophores impact commercial fisheries?

Ctenophores can significantly impact fisheries: 1) Large blooms of ctenophores can consume vast amounts of fish eggs and larvae, potentially reducing fish populations. 2) In some areas, invasive ctenophores have been linked to collapses in commercial fish stocks. 3) Ctenophores can also clog fishing nets and interfere with fishing operations. Understanding ctenophore population dynamics is thus crucial for effective fisheries management in affected areas.

17. How do ctenophores interact with other marine organisms besides predation?

Ctenophores have various interactions with other marine life: 1) Some small fish use ctenophores as temporary shelter. 2) Certain parasites specifically target ctenophores as hosts. 3) Some ctenophores form symbiotic relationships with photosynthetic algae, similar to corals. 4) Ctenophore mucus can serve as a substrate for various microorganisms. These interactions highlight the complex ecological roles ctenophores play in marine ecosystems.

18. What are the major types of ctenophores, and how do they differ?

There are two main types of ctenophores: 1) Tentaculate ctenophores have tentacles for catching prey (e.g., sea gooseberries). 2) Lobate ctenophores have large oral lobes instead of tentacles (e.g., Venus' girdle). They differ in body shape, feeding methods, and habitat preferences. Some ctenophores are spherical, while others are ribbon-like or have elaborate body extensions. These variations reflect adaptations to different marine environments and prey types.

19. What is the "combjelly paradox" in ctenophore biology?

The "combjelly paradox" refers to the surprising complexity of ctenophores despite their early evolutionary branching: 1) They have complex features like a nervous system and muscles, which are absent in simpler animals like sponges. 2) Yet, genetic studies suggest ctenophores may have branched off earlier than sponges in animal evolution. 3) This paradox challenges our understanding of how complex animal traits evolved and has led to debates about the early evolution of animals.

20. What is the ctenophore nervous system like, and why is it interesting to scientists?

The ctenophore nervous system is of great interest because: 1) It's a "nerve net" - a diffuse network of neurons without a central brain. 2) Despite this simple structure, ctenophores can perform complex behaviors. 3) Their neurons use a unique set of neurotransmitters, different from other animals. 4) This suggests the possibility of independent evolution of nervous systems in ctenophores, challenging our understanding of animal neurobiology.

21. How do ctenophores move through water?

Ctenophores move using their distinctive comb rows: 1) Each comb row consists of thousands of cilia. 2) These cilia beat in coordinated waves, propelling the animal through water. 3) By controlling different comb rows, ctenophores can move in any direction. 4) Some species also use muscular contractions of their body or lobes for additional movement. This unique locomotion method is highly efficient and allows for precise control of movement.

22. How do ctenophores digest their food?

Ctenophores have a more complex digestive system than many other simple animals: 1) They have a through-gut, with separate mouth and anal pores. 2) Food is broken down in a stomach-like structure. 3) Nutrients are distributed through canals that run throughout the body. 4) Some ctenophores can digest food externally by wrapping their bodies around prey and secreting enzymes. This efficient system allows them to process a variety of prey types.

23. How do ctenophores differ from cnidarians like jellyfish?

While both are gelatinous marine animals, ctenophores differ from cnidarians in several key ways: 1) Ctenophores use comb-like cilia for movement, while jellyfish use muscle contractions. 2) Ctenophores lack stinging cells (nematocysts) that are characteristic of cnidarians. 3) Ctenophores have a more complex digestive system with a through-gut, unlike the sac-like gut of cnidarians.

24. How do ctenophores reproduce, and what is unique about their embryonic development?

Ctenophores are hermaphroditic, possessing both male and female reproductive organs. They typically reproduce sexually, releasing eggs and sperm into the water. What's unique about their development is that the comb rows, a defining feature of ctenophores, are formed very early in embryonic development. This early specialization is different from many other animal groups and has implications for understanding animal evolution.

25. How do ctenophores maintain their buoyancy in water?

Ctenophores maintain buoyancy through several adaptations: 1) Their bodies are composed largely of water, making them close to neutrally buoyant. 2) They have a gelatinous composition that's less dense than seawater. 3) Some species can adjust their buoyancy by regulating ion concentrations in their bodies. These adaptations allow ctenophores to float effortlessly in the water column, conserving energy.

26. How do ctenophores feed, and what adaptations do they have for capturing prey?

Ctenophores are carnivorous and use various methods to capture prey: 1) Many species have two long, sticky tentacles that can be extended to catch small organisms. 2) Some use their large, expandable mouths to engulf prey whole. 3) Others create currents with their cilia to draw prey towards their mouths. Their transparent bodies also help them remain camouflaged while hunting.

27. What are colloblasts, and how do they function in ctenophores?

Colloblasts are specialized adhesive cells found on the tentacles of many ctenophore species. They function as follows: 1) When prey touches the tentacle, colloblasts burst open. 2) They release a sticky substance that adheres to the prey. 3) This allows the ctenophore to capture and hold onto its food before bringing it to its mouth. Colloblasts are unique to ctenophores and are an important adaptation for their predatory lifestyle.

28. What is the "ctenophore genome mystery" and why is it significant?

The "ctenophore genome mystery" refers to surprising findings from ctenophore genome sequencing: 1) Ctenophores lack many genes thought to be essential for animal development and function. 2) They have unique genes not found in other animals. 3) Their genome organization is different from other animal groups. This "mystery" suggests that ctenophores may have evolved many of their complex features independently, challenging our understanding of animal evolution and development.

29. What is unique about ctenophore embryology?

Ctenophore embryology has several unique features: 1) They exhibit determinate cleavage, where the fate of cells is determined very early in development. 2) The comb rows, a defining feature, form remarkably early in development. 3) Some species can produce larvae capable of feeding and even reproducing before reaching adulthood. These characteristics make cten

30. What role do ctenophores play in marine bioluminescence?

Ctenophores are significant contributors to marine bioluminescence: 1) Many species can produce light along their comb rows, creating beautiful displays. 2) Unlike many bioluminescent organisms, ctenophores often use calcium-activated proteins instead of the more common luciferin-luciferase system. 3) Their bioluminescence can be triggered by mechanical stimulation, creating sparkling effects in disturbed water. This makes ctenophores important subjects in the study of bioluminescence mechanisms and evolution.

31. What is unique about ctenophore muscle tissue?

Ctenophore muscle tissue is unique in several ways: 1) Unlike most animals, ctenophore muscles are derived from the mesoglea, not mesoderm. 2) They have smooth muscle-like cells that can contract but lack the striations seen in most animal muscles. 3) Despite this simple structure, ctenophores can perform complex movements. This unique muscle composition has implications for understanding the evolution of animal muscle tissues.

32. How do ctenophores contribute to marine carbon cycling?

Ctenophores play a role in marine carbon cycling: 1) They consume large amounts of small organisms, packaging this organic matter into larger, faster-sinking fecal pellets. 2) When ctenophores die, their bodies can rapidly sink, transporting carbon to the deep ocean. 3) Blooms of ctenophores can significantly alter local nutrient cycles. Understanding ctenophore population dynamics is thus important for modeling marine carbon fluxes and climate impacts.

33. How do ctenophores reproduce asexually?

While sexual reproduction is more common, some ctenophores can reproduce asexually: 1) Some species can bud off small pieces of their body that grow into new individuals. 2) Others can split in half (fission) to form two new ctenophores. 3) Some larval ctenophores can produce more larvae before reaching adulthood. Asexual reproduction allows rapid population growth under favorable conditions and is an important aspect of ctenophore ecology.

34. What is the significance of ctenophore statocysts?

Statocysts in ctenophores are gravity-sensing organs that: 1) Help the animal maintain orientation in the water. 2) Coordinate the beating of cilia in the comb rows for efficient swimming. 3) May play a role in detecting water currents. Unlike statocysts in many other animals, ctenophore statocysts are connected to cilia-bearing cells, allowing direct control of movement. This unique arrangement provides insights into the evolution of sensory systems in animals.

35. How do ctenophores survive in oxygen-poor environments?

Ctenophores have adaptations for low-oxygen conditions: 1) They can tolerate lower oxygen levels than many other marine animals. 2) Some species can reduce their metabolic rate in low-oxygen conditions. 3) Their gelatinous bodies have a high surface area-to-volume ratio, facilitating oxygen diffusion. 4) Some ctenophores may be able to store oxygen in their mesoglea. These adaptations allow ctenophores to thrive in environments that are challenging for other animals.

36. What is the role of mucus in ctenophore biology?

Mucus plays several important roles in ctenophores: 1) It helps in capturing and handling prey by making surfaces sticky. 2) It provides a protective coating against parasites and pathogens. 3) Some species use mucus strands to collect food particles from the water. 4) Mucus production can be a defense mechanism, confusing predators or making the ctenophore less palatable. Understanding mucus composition and production is important for comprehending ctenophore ecology and physiology.

37. How do ctenophores avoid predation?

Ctenophores have several strategies to avoid predation: 1) Many are transparent, making them difficult to see in water. 2) Some can rapidly regenerate lost body parts. 3) Their bioluminescence may startle or confuse predators. 4) Some species can quickly change direction or retract their tentacles when threatened. 5) A few ctenophores produce unpalatable compounds. These diverse strategies reflect the evolutionary pressures faced by these delicate animals in marine environments.

38. How do ctenophores contribute to marine snow formation?

Ctenophores contribute to marine snow (sinking organic particles) in several ways: 1) They produce mucus that can aggregate small particles. 2) Their fecal pellets are part of marine snow. 3) Dead ctenophores sink and become marine snow themselves. 4) In some cases, discarded feeding structures can contribute to particle formation. This process is important for the vertical transport of carbon and nutrients in the ocean, linking surface productivity to deep-sea ecosystems.