Cnidocyte vs Nematocyst: Difference and Comparison

Cnidocytes are specialized cells found in the phylum Cnidaria, responsible for delivering venom or capturing prey through the use of nematocysts. Nematocysts are complex organelles within cnidocytes that contain a coiled, barbed thread, capable of injecting venom or ensnaring prey upon trigger.

Key Takeaways

  1. Cnidocytes are specialized cells found in the tentacles of some aquatic animals, while nematocysts are the stinging organelles within cnidocytes.
  2. Nematocysts are used for defence and capturing prey, while cnidocytes can also be used for adhesive purposes or to create a protective shell.
  3. Both cnidocytes and nematocysts are found in cnidarians, such as jellyfish and corals, but not all cnidarians possess nematocysts.

Cnidocyte vs Nematocyst

The difference between a cnidocyte and a nematocyst is that the cnidocyte assists the thread, cnidocil, to eject with the help of the nematocyst that propels it out and into the waters.

Cnidocyte vs Nematocyst

Cnidocyte is a capsule present on a cnidarian’s body that ejects thread-like projections as a defence mechanism. It not only allows the organism to escape danger but also assists in hunting for food and adherence to the substratum during locomotion.

As soon as the species senses danger, the capsule makes the cell explode and release the hair-like cnidocil, which is not only a mechanical but also a chemoreceptor. This action occurs in milliseconds injecting an enzyme to stun or injure the predator.

On the other hand, a Nematocyst is the explosion cell (a subcellular structure or organelle) that ejects the cnidocil; the hair-like projection is released when the trigger is activated, containing venom that also helps in locomotion.

However, this function is enabled after a certain time. It only works when the organism has matured. The cells that produce nematocysts are called nematoblasts.

Ewer, in 1947 defined the functional categories of nematocysts as prey capture (penetrants), defence (solvents), and adherence during locomotion (glutinous).

The nematocysts contain the barbed or venomous coiled thread that is released at times of emergency. The string contains hypnotizing, a mixture of phenols and proteins.

Comparison Table

FeatureCnidocyteNematocyst
DefinitionA specialized cell containing a stinging organelle.The organelle itself located within the cnidocyte, responsible for delivering a sting.
StructureThe cnidocyte consists of a capsule, a cnidocil (trigger), and the nematocyst inside.The nematocyst is a capsule-like structure containing a coiled tubule and venom.
FunctionThe entire cnidocyte acts as a unit to capture prey and defend against predators.The nematocyst fires the tubule and injects venom when triggered, causing harm to the target.
DevelopmentCnidocytes develop from cnidoblasts, immature cnidocytes.Nematocysts are produced within the cnidocyte and develop inside the capsule.
SpecificityDifferent cnidocyte types exist, each containing specialized nematocysts with varying functions (e.g., penetration, entanglement).The specific type of nematocyst determines its function and venom content.

What is a Cnidocyte?

Cnidocytes, also known as cnidoblasts, are highly specialized cells found exclusively in the phylum Cnidaria, which includes jellyfish, sea anemones, corals, and hydras. These cells play a crucial role in the predatory and defensive mechanisms of cnidarians.

Structure of Cnidocytes

Cnidocytes possess a distinctive structure tailored for capturing prey and defense. At their apex, cnidocytes contain a specialized organelle called the nematocyst, which is enclosed within a capsule. The nematocyst consists of a long, coiled tubule and a barbed, venomous, tip. This structure is finely tuned to inject toxins into prey or potential threats upon stimulation.

Function of Cnidocytes

  1. Predation: Cnidocytes are primarily utilized for capturing prey. When triggered by touch or chemical stimuli, such as those emitted by potential prey, the cnidocyte discharges its nematocyst with remarkable speed. The nematocyst penetrates the prey’s body, injecting venom and immobilizing it, allowing the cnidarian to consume its catch.
  2. Defense: Cnidocytes also serve as a vital defense mechanism against predators. When threatened, the cnidarian can discharge its cnidocytes, releasing nematocysts that can deter or injure the predator. Some cnidarians, like jellyfish, possess potent venom in their nematocysts, enhancing their defensive capabilities.

Variability in Cnidocyte Types

Cnidocytes exhibit considerable diversity across different species of cnidarians. While the basic structure and function remain consistent, variations exist in the size, shape, and potency of nematocysts. This diversity allows cnidarians to adapt to various ecological niches and prey types, optimizing their predatory and defensive strategies.

cnidocyte

What is a Nematocyst?

Nematocysts are intricate and specialized organelles found within the cnidocytes of cnidarians, playing a fundamental role in their predatory and defensive strategies. These organelles are highly adapted for capturing prey and deterring predators, embodying the remarkable evolutionary innovations of cnidarians.

Structure of Nematocysts

  1. Capsule: Each nematocyst is enclosed within a capsule, which serves as a protective covering. The capsule is composed of a tough, resilient material, ensuring the integrity of the nematocyst until it is discharged.
  2. Coiled Tubule: Within the capsule lies a tightly coiled tubule, resembling a miniature harpoon. This tubule is under high internal pressure due to the osmotic potential of the fluid inside, storing potential energy necessary for rapid deployment.
  3. Barbed Tip: At the end of the tubule is a barbed or spiny tip, designed to penetrate the outer layers of prey or predators upon discharge. This barb enhances the efficiency of the nematocyst in immobilizing or injuring the target.

Function of Nematocysts

  1. Predatory Mechanism: Nematocysts serve as the primary weapon in the predatory arsenal of cnidarians. When stimulated by mechanical or chemical cues, such as the presence of prey, the cnidocyte housing the nematocyst undergoes rapid activation. This triggers the expulsion of the nematocyst, which rapidly extends its tubule and delivers venom into the target, incapacitating or killing it.
  2. Defensive Strategy: In addition to predation, nematocysts play a crucial role in defense against predators. When a cnidarian is threatened or attacked, it can discharge its nematocysts as a defensive measure. The venomous content of the nematocysts can deter or harm potential predators, providing the cnidarian with an effective means of protection.

Diversity of Nematocysts

Nematocysts exhibit remarkable diversity across different species of cnidarians. Variations in size, shape, and venom potency contribute to the adaptability of cnidarians to various environmental conditions and prey types. This diversity underscores the versatility of nematocysts as evolutionary adaptations, enabling cnidarians to thrive in diverse marine ecosystems.

nematocyst

Main Differences Between a Cnidocyte and Nematocyst

  • Definition:
    • Cnidocyte: Specialized cells found in cnidarians responsible for housing and deploying nematocysts.
    • Nematocyst: Specialized organelles within cnidocytes, serving as the actual stinging apparatus.
  • Structure:
    • Cnidocyte: Entire cell structure containing various organelles, including the nematocyst.
    • Nematocyst: Intracellular organelle enclosed within the cnidocyte, consisting of a capsule, coiled tubule, and barbed tip.
  • Function:
    • Cnidocyte: Responsible for the activation and deployment of nematocysts in response to stimuli such as touch or chemical cues.
    • Nematocyst: Acts as the primary offensive mechanism, injecting venom or ensnaring prey upon discharge triggered by the cnidocyte.
  • Role:
    • Cnidocyte: Facilitates the delivery and activation of nematocysts for both predation and defense.
    • Nematocyst: Executes the actual stinging action, either immobilizing prey or deterring predators through venom injection or physical entrapment.
Difference Between Cnidocyte and Nematocyst
References
  1. http://www.ijdb.ehu.es/web/paper.php?doi=10.1387/ijdb.113472ab
  2. https://science.sciencemag.org/content/243/4898/1589.abstract

Last Updated : 01 March, 2024

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17 thoughts on “Cnidocyte vs Nematocyst: Difference and Comparison”

  1. This is a very informative article, it’s necessary to understand the basic defense mechanisms of organisms. It’s interesting to know that even the smallest living organisms have developed methods to protect themselves.

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