Difference Between Cnidocyte and Nematocyst

Main Difference – Cnidocyte vs Nematocyst

Cnidaria refers to an animal phylum that predominantly contains marine species. It consists of jellyfish, anemones, corals, and hydrae. Cnidarians are diploblastic animals. The most striking feature of cnidarians is cnidocytes they use to capture the prey. Cnidocytes are also called cnidoblasts or nematocytes. They are ectodermal cells found near the tips of the tentacles. Some cnidocytes can be found in the endoderm as well. The main difference between cnidocyte and nematocyst is that cnidocyte is a type of cell that helps predation of cnidarians whereas nematocyst is an organelle consisting of a coiled, thread-like stinger.

Key Areas Covered

1. What is a Cnidocyte
     – Definition, Structure, Function
2. What is a Nematocyst
     – Definition, Structure, Discharge Mechanism
3. What are the Similarities Between Cnidocyte and Nematocyst
     – Outline of Common Features
4. What is the Difference Between Cnidocyte and Nematocyst
    – Comparison of Key Differences

Key Terms: Cnidaria, Cnidoblast, Cnidocyte, Hypnotoxin, Nematocyst, Operculum, Predation, Sting

Difference Between Cnidocyte and Nematocyst - Comparison Summary

What is a Cnidocyte

Cnidocyte refers to a specialized cell containing cnidocyst, which is involved in the capturing the prey in cnidarians. It is also called cnidoblast or nematocyte. Cnidocytes can be found on the tentacles and hypostome in sea anemone, jellyfish, corals, and hydrae. The cnidocytes are used to prey on fish and crustaceans. They consist of a single, giant, secretory organelle known as a nematocyst. The discharge mechanism of nematocyst is shown in figure 1.

Difference Between Cnidocyte and Nematocyst

Figure 1: Discharge Mechanism of Nematocyst

The cnidocyte is a rounded or oval-shaped cell. The nucleus of the cnidocyte is conspicuous. It lies on the basal side of the cell. A pyriform sac, which is filled with a toxin known as hypnotoxin, is present inside the cnidocyte. The hypnotoxin is a mixture of proteins and phenols. The outer end of the sac is invaginated into a tubular filament coiled inside the sac itself. The base of the tubular filament is swollen to form a butt. The butt carries three spines known as barbs. The lid that covers the sac is known as operculum. The discharge of the tubular filament is triggered by a hair-like process called cnidocil. The restraining thread known as lasso and the contractile muscle fibrils at the base of the cnidocyte prevent the throwing out of the nematocyst from the cell.    

What is a Nematocyst

Nematocyst refers to an organelle inside the cnidocyte, consisting of an ejectable tread thread that causes a sting. It is also called cnidocyst or cnida. The nematocyst is discharged due to chemical or mechanical stimuli received by the cnidocil. Generally, in the resting stage, the cnidocyte is not permeable to water. However, due to the presence of hypnotoxin inside the cnidocyte, the cell is hypertonic to the external water. Upon stimulation, the permeability of the cnidocyte increases and the water rushes into the cell. This eventually increases the hydrostatic pressure inside the sac that contains hypnotoxin, opening its lid. The thread tube is discharged in a great force due to the hydrostatic pressure. It would deeply penetrate the tissues of the victim, injecting the toxin. A discharged nematocyst is shown in figure 2.

Main Difference - Cnidocyte vs Nematocyst

Figure 2: Discharged Nematocyst

Around 30 different nematocyst types can be found among cnidarians. They can be mainly divided into three groups: penetrant, glutinant, and volvent. The largest and most complex nematocysts are penetrants. Glutinant is a sticky surface used to capture the prey. The volvent contains short, thick, and spineless nematocysts.

Similarities Between Cnidocyte and Nematocyst

  • Cnidocyte and nematocyst are two structures found in the ectoderm of cnidarians.
  • Both cnidocyte and nematocyst are involved in the capturing of the prey.

Difference Between Cnidocyte and Nematocyst

Definition

Cnidocyte: Cnidocyte refers to a specialized cell, containing cnidocyst, which is involved in capturing the prey in cnidarians.

Nematocyst: Nematocyst refers to an organelle inside the cnidocyte, consisting of an ejectable thread that causes a sting.

Significance

Cnidocyte: Cnidocyte is an ectodermal cell in cnidarians.

Nematocyst: Nematocyst is the organelle that occurs inside the cnidocyte.

Alternative Names

Cnidocyte: Cnidocytes are also called cnidoblasts or nematocytes.

Nematocyst: Nematocyst is also called cnidocyst or cnida.

Role

Cnidocyte: Cnidocytes are stinging cells used in defense and capturing prey.

Nematocyst: Nematocyst contains toxins to be injected into the predator or prey.

Conclusion

Cnidocyte and nematocyst are two structures that aid in the capturing of the prey by cnidarians. Cnidocyte is an epidermal cell that contains the nematocyst. Cnidoctes can be found in the tentacles of the cnidarians. The nematocyst is the organelle inside the cnidocyte used to inject toxins into the prey. The main difference between cnidocyte and nematocyst is the role of each structure in the capturing of the prey by cnidarians.

Reference:

1. “Cnidocyte” on Revolvy.Com.” Trivia Quiz, Available here.
2. “Nematocyst.” Encyclopædia Britannica, Encyclopædia Britannica, inc., 6 Feb. 2014, Available here.

Image Courtesy:

1. “Nematocyst discharge” By The original uploader was Spaully at English Wikipedia – Transferred from en.wikipedia to Commons., Public Domain) via Commons Wikimedia
2. “Nematocyst-discharged” Public Domain) via Commons Wikimedia

About the Author: Lakna

Lakna, a graduate in Molecular Biology & Biochemistry, is a Molecular Biologist and has a broad and keen interest in the discovery of nature related things

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