Phylum Aschelminthes: Characteristics, Case Study & USA 10 grade( NSSG )

Overview: What are Roundworms?Aschelminthes are Pseudocoelomate , Triploblastic, bilaterally symmetrical roud worms with organ level of organisation. They first developed muscular pharynx with complete alimentary Canal.

Before learning about Roundworms, check out our detailed guide on Platyhelminthes (Flatworms) here

Table of content

Introduction: What are Roundworms?
Key Anatomical Features & Pseudocoelom
Sexual Dimorphism in Aschelminthes
Pathophysiology: Common Human Infections
Case Study 1: Diagnosis of Elephantiasis
Prevention & Public Health Measures
Review Quiz for Grade 10 Students

Key Concept:

The "Tube-within-a-tube" Body Plan

Roundworms are a major evolutionary milestone. Unlike earlier animals, they have a complete digestive system.
This plan signifies that a tube is present with in another tube
Under this plan, a smaller tube (the digestive tract) running inside a larger tube (the body wall).
This allows the worm to eat, digest, and get rid of waste all at the same time—making energy production much more efficient.
This plan has major evolutionary significance because it led to develop complete digestive system.
It also separate digestive system from other body system like circulatory system.

The Pseudocoelom

Roundworms are Pseudocoelomates because coelom is not lined by the mesoderm.
The space between gut and body wall is filled with a fluid but not mesoderm .
A fluid-filled body cavity that is not lined by mesoderm, called pseudocoelom or false coelom.
The fluid between the alimentary canal and body wall is called Hydrostatic fluid .
It acts as a Hydrostatic Skeleton, providing pressure to help the worm move and maintain its shape.
In term of evolution, pseudocoelom provides space for other body organs and It enables Roundworms to survive in variable habitats.
It also traces the path the origin of coelomate animals.

Syncytial cuticle

The Epidermis is syncytial (a continuous layer of multinucleated cytoplasm), which secretes a thick, non-living protective Cuticle."
Syncytial cuticle is a protective covering formed by the epidermis. It is not made up of cells .
Actually It is a multinucleated cytoplasm.
It provides protection of parasites with in the body of host.
It also stores fat which act as reserve food for the parasite.
Roundworms get protection from digestive juices of host and acidic pH inside the gut.

Muscular Pharynx

Aschelminthes have a well-developed, highly muscular pharynx. This is a key feature of their complete digestive system.
Sucking Action: The muscles in the pharynx create a powerful sucking action that helps the worm pull food (liquid or semi-liquid) into its alimentary canal.
Complete Canal: Unlike earlier phyla, they have a complete digestive tract with both a mouth and an anus.
Function: It acts as a pump, moving nutrients through the "tube-within-a-tube" body plan efficiently.

Sexual dimorphism

Sexes are separate, male and female are distinct.
Female roundworms are often longer than males, and the male has a curved posterior end."
Examples of Aschelminthes
Ascaris lumbricoides (Roundworm)
Ascaris is long round worm which can be up to more than 30 cm but female is always longer than male.
Ascaris show sexual dimorphism. Male is usually shorter with folded end at one side.
Ascaris has non cellular cuticle covering on body to get protection from digestive enzyme of host

Digestive system is well developed in with various digestive organs.
Nervous system include nerve ring with numerous nerve cords.
Embryonated egg is infective stage of Ascaris. These eggs are passed out with the stool of infective person and make contaminated the soil.
Egg is ingested by host when it comes contact with contaminated soil into host body.
Egg is developed into Rhabditiform larva and than into adult Ascaris.
Wuchereria bancrofti (Filarial worm)
It is commonly called as Filaria worm.
It show sexual dimorphism. Adult female is usually longer with rounded ends and male is shorter than female. The tail of male is centrally curved.
Wuchereria has 15 pairs of sensory organs.
Wuchereria

It resides in lymphatic system of Human but may also found in blood.
Alimentary canal include Muscular pharynx oesophagus intestine and anus. The mouth is present without oral lips.
Female genital pore is present as vulva whereas male has cloaca.
Penial setae or copulatory Spicules are present in male.
Microfilareae is larval stage of wuchereria found in blood of human.
Ancylostoma duodenale (Hookworm)

It is commonly called as Hook worm.
Adult female is usually longer with rounded ends and male is shorter than female.
Hook worm is small cylinder and white or pinkish in color.
It has sharp teeth or cutting plate in their buccal capsule.
Ancylostoma
Male Hook worm has bursa with two Spicules.
Female Hook worm has vulva. It lay 10000 to 30000 eggs per day.
It create various health complex like anemia , Malnutrition and protein loss.

Pathophysiology: Common Infections in Humans

Case Study 1: The Swollen Limb Mystery

Observation : A team of health workers went to a village but team does not have a any Doctor. Members observed the swelling in lower limb in some villagers and mentioned about a moderate ditch with stagnant water in their report. Now Doctor instruct ed to team by sending a report.

Diagnosis

Symptoms: Inflammation in lymph vessels of lower limb. It may also affect genital organs.
Disease: Elephantiasis (Lymphatic Filariasis).
Causative Agent: Filarial worms (Wuchereria bancrofti) &
Mode of Transmission: Bite of an infected female Culex mosquito.

Pathophysiology:

The worms live in the lymphatic vessels, causing chronic inflammation and blockage, which leads to massive swelling.

Doctor's Action Plan (Prevention):

Source Reduction: Eliminate stagnant water or use larvicides (like Gambusia fish or chemical sprays).
Personal Protection: Use of mosquito nets and repellents.

3. NGSS Science & Engineering Practices (SEP)

Outline Point: Observation Challenge.

Task: If you were looking under a microscope, how would you distinguish a Roundworm from a Flatworm based on movement?

Answer: Roundworms have only longitudinal muscles, so they move in a whipping, thrashing motion, whereas Flatworms glide using cilia.

4. Diagram Labeling Activity

Outline Point: "Label the Worm" Challenge.

Task: Provide an unlabeled diagram of a Roundworm and ask students to identify the Mouth, Pseudocoelom, Intestine, and Anus.

3. Lab Case Study: Ascaris lumbricoides

In US high schools, students often study the Ascaris life cycle to understand parasitic transmission.

Transmission: Usually through contaminated soil or unwashed vegetables.
Prevention: The "Wash Your Hands" campaign is the best defense against these parasites.

USA High School Biology:

Time: 30 Minutes | Total Marks: 20

Section A: Multiple Choice (10 Marks)

Roundworms are the first animals to have a ________ digestive system.
- A) Incomplete
- B) Complete (Mouth to Anus)
- C) Absent
- D) Gastrovascular
The Hydrostatic Skeleton in nematodes is provided by:
- A) Bones
- B) Chitinous Shell
- C) Fluid-filled Pseudocoelom
- D) Muscular Foot
Which of these best describes "Sexual Dimorphism" in Ascaris?
- A) Males and females look identical.
- B) Males are longer than females.
- C) Females are longer and males have a curved tail.
- D) They are hermaphrodites.

Section B: Critical Thinking (10 Marks)

Evolutionary Analysis: Why is a "complete digestive tract" (mouth and anus) an advantage over a "gastrovascular cavity" (one opening)? (4 Marks)
Data Interpretation: If a soil sample contains 500 nematode eggs per gram, explain two ways a local farm could prevent an outbreak in the community. (6 Marks)

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