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Difference Between Prostomium and Peristomium

Main Difference

The main difference between Prostomium and Peristomium is that Prostomium is present in front of the mouth of the annelids, whereas Peristomium is present around the introductory part of the mouth.

Prostomium vs. Peristomium

Prostomium usually refers to the head portion of the annelids that is present in front of the mouth segment, while peristomium refers to the front portion of the annelids that surround the mouth. The prostomium is present in the head segment of the body of annelids, whereas peristomium is present in the initial part of the body of annelids. The prostomium is considered as the older segment present in the annelids body; on the other hand, peristomium is generally considered as the oldest part of the body.

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The prostomium is made up of the various sensory organs and the mouth of the annelids; on the contrary, peristomium does not have any sensory organs or mouth part in the annelids body. The true segment present in the body of annelids is prostomium; on the flip side, peristomium is not deliberated as a true segment that is present in the body of annelids. The main function of the prostomium is to serve in pushing the body of annelids as a wedge into the soil to firmly open the cracks where the earthworm used to live; on the other hand, surrounding the opening of the mouth in the body of annelids is the main function of peristomium that it performs.

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Prostomium as a sensory function contains various sensory organs such as nuchal organ, caruncle, and eyespots of annelids; on the contrary, peristomium usually does not have any sensory function for the performance in the annelids body. As an appendage in prostomium, the mouth region is present; on the flip side, as an appendage function in peristomium, the chaetae are present. Prostomium contains two antennae and two large, two-segmented palps; on the other hand, peristomium contains four pairs of tentacular cirri and sometimes usually have feeding palps.

Comparison Chart

ProstomiumPeristomium
The prostomium is known as the section that is existing in anterior of the mouth of the annelids.Peristomium is generally known as the introductory part of the mouth of the annelids.
Refers To
The head portion of the annelidsThe front portion of the annelids
Location
Present in the head segment of the body of annelidsPresent in the initial part of the body of annelids
Segmental Age Difference
Consider the older segment in the body.Consider the oldest part of the body.
Composition
Made up of the various sensory organs and the mouth of the annelidsDoes not have any sensory organs or mouth part in annelids body
True Segment
It considers the true segment present in the body of annelids.It is not deliberated as a true segment that is present in the body of annelids.
Functions
Serves in pushing the body of annelids as a wedge into the soil to firmly open the cracks where the earthworm used to liveSurrounding the opening of the mouth in the body of annelids
Sensory Functions
It contains various sensory organs such as the nuchal organ, caruncle, and eyespots of annelids.Do not have any sensory function for the performance in the body.
Appendages
The mouth is the region is present.The chaetae are present.
Contains
It contains two antennae and two large, two-segmented palpsIt contains four pairs of tentacular cirri and sometimes usually have feeding palps.
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What is Prostomium?

Prostomium usually mentions the head portion, which is present in front of the mouth, which is usually a lip-like addition or a small shelf-like addition in the dorsal body of the annelids. In other words, Prostomium is generally a minor plump portion, which extends the mouth of an earthworm. Prostomium assists the organism push into the soil and is sensual in function. The body of annelids is usually divided into three parts as trunk, pygidium, and prostomium.

The prostomium is known as the anterior part of the annelids body, and the mouth portion is present just after the prostomium. In some annelids, a tongue-like structure is a present overhead the mouth, and the region which always surrounds the mouth part of the annelids is known as prostomium. The true segment present in the body of annelids is prostomium. The bulkiness in the body of annelids is formed by the trunk that contains various segments.

The particulate structure in the body is pygidium that is present at the posterior portion of the annelids. When segments added in the front of the pygidium, this usually results in the growth of the annelid. The skin and the prostomium part of the skin collect sensory information from the surrounding or the environment by containing sensory receptors. Light-sensitive structures are known as eye-spots, also formed the prostomium. The prostomium is deliberated as the mature fragment present in the annelid’s body.

Prostomium contains various other kinds in posterior additions or elevation with the sensory function called the caruncle and having another sensory function called the nuchal organ, which is usually a ciliated groove or pit at the posterior part of prostomium structure. In prostomium, some appendages like structures such as cirri, palps, or tentacle also present. The occurrence of these sensual structures also offers exceptional distinguishing structures to the prostomium. The main function of the sensual structures is to distinguish different, physically uncertain things from the external environment.

Functions

  • Contains eyes and antennae
  • When the annelid is nurturing, it often functions as a type of over lip.
  • Form and arrangement of prostomium are also vital for annelid systematics.
  • The main function of the prostomium is to serves in pushing the body of annelids as a wedge into the soil to firmly open the cracks where the earthworm used to live.

What is Peristomium?

Peristomium generally mentions the front portion, which surrounds the mouth portion of the annelids. In other words, the first body part in the earthworm or annelid is known as the peristomium. Peristomium usually surrounds the mouth opening. It mentions the frontal portion of the annelids.

Normally, the peristomium is not deliberated as a true segment in the annelid’s body because it doesn’t contain any sensory organ. The chaetae are present in the peristomium, which are the appendages in various annelids. The peristomium is known as the oldest part of the annelid’s body because all the growth of annelids takes place from the posterior part. Peristomium is present right after the peristomium that consists of 4 pairs of tentacular cirri, mouth, and sometimes may contain feeding palps.

Peristomium can be contained in the eversible pharynx if it is existing, and when it is inverted, 20 segments could be filled up into it, but this is depending on the type of species. The peristomium and prostomium could sometimes be merged, either entirely separate or including a combined arrangement of a peristomial loop and a tentacular top. So, various times it is said that peristomium is present in the prostomium. Surrounding the opening of the mouth in the body of annelids is the main function of the peristomium that it performs.

Key Differences

  1. In the body of annelids, the prostomium is present in the head segment, whereas peristomium is existent in the primary part of the annelids body.
  2. The head portion of the annelids is usually the prostomium, while the front portion of the annelids is generally the peristomium.
  3. The older segment present in the annelids body is considered as the prostomium; on the other hand, the oldest part of the body is usually considered as the peristomium.
  4. The prostomium is formed from the mouth of the annelids and many sensory organs and; on the contrary, peristomium does not contain any mouthpart or sensory organs in the annelids body.
  5. The prostomium is the real part present in the body of annelids; on the flip side, in the body of annelids, the peristomium that is present is not considered as a real part.
  6. The body of annelids work in assertive into the soil to strongly open the cracks where the earthworm used to live, and it is the main function of the prostomium; on the other hand, the main function of peristomium is that it surrounds the opening of the mouth in the body of annelids.
  7. Various sensory organs like a nuchal organ, caruncle, and eyespots of annelids are present in prostomium as a sensory function; on the contrary, for the sensory performance in the body of annelids, the peristomium does not have any sensory organs.
  8. The mouth area is present in prostomium as an appendage; on the flip side, the chaetae are present in peristomium as a function of the appendage.
  9. Prostomium consists of dual antennae and binary large, double-segmented palps; on the other hand, peristomium consist of feeding palps and sometimes commonly has four pairs of tentacular cirri.

Conclusion

The above discussion concludes that the prostomium contains the head portion of the body of annelids and contains mouth and sensory organs like a nuchal organ, and eye-spots. The peristomium is generally the first segment of the body of annelids and usually surrounds the mouth.

Janet White

Janet White is a writer and blogger for Difference Wiki since 2015. She has a master's degree in science and medical journalism from Boston University. Apart from work, she enjoys exercising, reading, and spending time with her friends and family. Connect with her on Twitter @Janet__White