Exploring the World of Nematodes: From Anatomy to Taxonomy


Updated: 4 Feb 2024

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Do you know how the nematodes eat and digest their food? Your every question will be answered in this blog.

There is much more fascinating information about them. Moreover, We will also discuss the classification of nematodes in detail.

Let’s delve into a comprehensive understanding of nematodes. So, without any further delay, let’s begin!

Morphology of Nematodes

Body wall

The body wall keeps things cozy inside, surrounding a fluid-filled space that’s always under a little pressure. The body wall consists of the following:

Cuticle

This colourless, semipermeable, and tough layer serves a protective and skeletal function. It may be smooth or ornamented with annulations. This layer varies at different stages of development and is the most complex structure of the nematode body.

Furthermore, it is divided into three layers, each containing numerous sub-layers.

Cortex

This layer is like the tough, outer skin of a nematode, but friendlier! It’s clear, kind of like a window, and has these cool, regularly spaced patterns called annulations. Imagine it as the fancy outer jacket that keeps the nematode safe and sound.

The cortex is divided into further layers.

  • Thermolabile layer

It gives impermeability. It is made of wax and sterol.

  • Osmophilic layer

It gives permeability.  

Matrix

This is the middle layer, featuring a uniform and homogeneous structure.

Inner basal

The outer layer called the cortex, is tightly connected to the matrix.

Chemically, the cuticle contains

Albumins = 25 %

A collagen = 29 %

A glycoprotein = 33 % 

Functions of Cuticle

  • The cuticle plays a crucial role in the development of lips, setae, and sensory organs such as amphids, deirids, and phasmids.
  • It also forms invaginations in structures like the rectum, vagina, mouth, cloaca, and excretory pore.
  • In certain male species, there are lateral extensions of the cuticle in the tail, known as caudal alae or copulatory bursa.
  • The body wall actively controls water movement across the cuticle to uphold high internal pressure.

Hypodermis

A thin layer beneath the cuticle is called a hypodermis. It is a living cellular layer. This hypodermis features four longitudinal thickenings that extend into the pseudocoel, forming bands referred to as chords.

The chords contain the nuclei of the hypodermal cells. In most nematodes, there are four such chords, including

  • 2 lateral chords
  • 1 dorsal chord
  • 1 ventral chord

Functions of Hypodermis

  • The hypodermis plays a crucial role in the nematode’s life cycle. It produces enzymes essential for digesting existing cuticles and secretes new ones. This process occurs four times throughout the nematode’s life.
  • But that’s not all – the hypodermis is also a storage hub for important nutrients like lipids and glycogens. In plant parasitic nematodes, it’s like their energy backpack. This energy is used while the nematode moves about in the soil, without feeding, hunting for a host.

Digestive System

The nematode’s digestive system contains a tube protruding from the oral orifice to the posterior orifice/anus. The digestive system is divided into four parts:

  • Stoma (mouth)
  • Esophagus
  • Intestine
  • Anus

Mouth

The mouth of a nematode is of different shapes depending upon the mode of feeding. A barrel-shaped mouth nematode always keeps its mouth open to engulf bacteria. Carnivorous nematodes have teeth in their mouth.

Plant parasitic nematodes are equipped with spears or stylets because they do not bite or engulf the roots so they are provided with stylet. The stylet is moveable it is so fast that it penetrates the cell 100 times.

The anterior part is pointed and called a conus because it resembles a cone. At the base, there are three rounds called knobs. The middle part is the shaft and is hard.

Nematodes are identified by the knob. In the middle of the nematode, there is a minute tube called the lumen of the stylet. When nematodes suck anything, it will pass through the lumen.

There are two types of stylets:

  • Stomatostylet
  • Odontostylet

Esophagus

It is a muscular tube that originates from the base of the stylet and ends at the basal valve. It contains glands in its walls or has glands attached to it, with ducts leading into the lumen. It is subdivided into 4 regions.

  • Procorpus

The first swelling, located in the anterior portion, is called the procorpus.

  • Metacorpus

The swelling which is in the middle is called metacorpus. It is also known as a median bulb.

  • Isthmus

The narrow section that connects the two large portions is called the isthmus. It connects the metacorpus to the basal bulb.

  • Basal bulb

This swelling at the base or just anterior to the intestine usually contains esophageal glands.

The nerve ring is present on the central part of the esophagus and it is the brain of the nematode. At the junction of the esophagus and intestine, a valve is present which is known as the esophageal intestinal valve, simply known as cardia. This valve prevents the backward movement of nutrients.

Intestine

The nutrients after passing from the esophagus come to the intestine where the food is digested. The intestine is made up of large cells that may have finger-like projections called microvilli, which face the lumen to increase surface area for absorption. When viewed under a light microscope, the intestine appears dark due to its dense cell contents.

Anus

The intestine connects to the rectum through the intestine-rectal valve and ultimately opens at the anus. The anus is kept closed by the high internal pressure within the nematode’s body. Muscles extending from the anus to the body wall are responsible for opening the anus during the process of defecation.

Classification of Plant Parasitic Nematodes

The systematic arrangement of living organisms into groups based on evolutionary trends and natural relationships is called classification. Nematodes belong to the kingdom Animalia or phylum Nematoda. 

Phylum nematoda is divided into two classes, these classes are based on sensory organs called phasmids which are located in caudal ala. The two classes of nematodes are Phasmidia (Secernentea) and Aphasmidia (Adenophorea).

Distinctions between Classes

PhasmidaAphasmida
Phasmids are presentPhasmids are not present
Amphids will open on the headAmphids open behind the head
The esophagus is made up of procorpus, metacorpus, isthmus, and basal bulbThe esophagus is cylindrical with an enlarged base
Caudal glands are present in class PhasmidaCaudal glands are not present in class Aphasmida
Bursa is common in this classBursa is rare in this class
Infrequent in waterCommonly found in water

Differences between Tylenchida and Aphelenchida

The class Secernentea is divided into many orders but we will focus on two orders viz.

TylenchidaAphelenchida
Anterior to the median bulb, into the lumen of the esophagus, dorsal esophageal glands openInto the median bulb, the dorsal esophageal gland always opens up
The median bulb is round and not very large. It does not occupy the whole diameterThe median bulb is angular and covers the whole diameter
Males often have bursaMales are without bursa except for Aphelenchus and Metaphelenchus

Differences between Dorylaimida and Triplonchida

Class Adenophorea has many orders but we will discuss only two orders because these are related to plant parasitic nematodes.

DorylaimidaTriplonchida
Amphids are of variable shapes such as round, spiral, multispiral, etcAmphids are post-labial or pouch-like
The anterior esophagus is a narrow tube and the posterior portion is swollen and muscularThe end portion is swollen while the anterior side of the esophagus is narrow, pyriform to elongate
The excretory duct is absent or weakly presentThe excretory duct is present
Males are with paired testes (Diorchic)Males are with single testis (Monorchic)

Differences between Tylenchida and Dorylaimida

TylenchidaDorylaimida
They have a narrow and pointed styletThey have a short and broad stylet
The esophagus is divided into four portions i.e.  procorpus, metacorpus, isthmus, and basal bulbThe esophagus is of cylindrical shape
Cuticle have distinct annulationsThe cuticle is not visible

Conclusion

In this blog, we have covered numerous topics in a detailed yet easily understandable manner. We want to emphasize that this level of concise information can hardly be found elsewhere. Every aspect of classification related to our topic is thoroughly explored.

We trust you’ll discover this blog to be a valuable source of information. Your satisfaction is our primary concern whenever we create content. We make every effort to meet your expectations.

Don’t hesitate to Contact Us through email about any queries, concerns, or issues you may have. You’re always welcome!

FAQs

Some potential questions that might help you find the answers you might require:

Name the layers of the cortex.
  • Thermolabile layer
  • Osmophilic layer
What is a bursa?

In certain male species, there are lateral extensions of the cuticle in the tail, known as caudal alae or copulatory bursa.

How many chords are there in nematodes?

In most nematodes, there are four such chords, including

  • 2 lateral chords
  • 1 dorsal chord
  • 1 ventral chord
Name the parts of the digestive system.
  • Mouth
  • Esophagus
  • Intestine
  • Anus
How many types of stylet are present?

There are two types of stylets.

  • Stomatostylet
  • Odontostylet
How can you define lumen?

In the middle of the nematode, there is a minute tube called the lumen of the stylet. When nematodes suck anything, it will pass through the lumen.

What connects the metacorpus to the basal bulb?

The narrow section which connects the two large portions is called the isthmus. It connects the metacorpus to the basal bulb.

Define the term microvilli.

The intestine is made up of large cells that may have finger-like projections called microvilli, which face the lumen to increase surface area for absorption.

Define the term cardia.

At the junction of the esophagus and intestine, a valve is present which is known as the esophageal intestinal valve, simply known as cardia.


Dr. M Awais

Dr. M Awais

This is Awais. I am a phyto doctor. I have studied plants my whole life. Plants are my best friends. I have gathered detailed information about plants. My brilliant team is always ready to accept the challenges. Together, we find the solutions for our clients.

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