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Phylum Nematoda

Examples

Roundworms◦ Dioctophyma renale – Inhabit the kidney, very large.

Examples

Roundworms◦ Ancylostoma duodenale – Also known as Hookworms, these live in

the small intestine and feed off of the blood.

Examples

Roundworms◦ Trichinella spiralis – Cause trichinosis, found in pigs and other

animals such as bears.

Examples

Roundworms◦ Ascaris lumbricoides – The most common of the roundworms, as

they infect as many as 1 billion people worldwide.

Introduction

Phylum Nematoda

◦ Many are microscopic parasites, but some

species can reach extraordinary lengths –

sometimes over 1 m

◦ Very abundant – widespread throughout the

world

◦ Consists of over 90,000 species

◦ Free-living and parasitic species

Free living species are important in the ecology of

soil -> they function as decomposers

Features

◦ “round” worms

◦ Free-living or parasitic

◦ Bilateral symmetry

◦ Cephalization, -- but not very well-defined

◦ Tissues formed from 3 true cell layers in embryo

Ectoderm, mesoderm, endoderm

◦ Unsegmented

◦ Internal organs found in the pseudocoelom

◦ Digestive tract with 2 openings (tube within a tube)

◦ Mouth and anus

◦ Body is covered with a thick cuticle

Body Plan

Pseudocolem

Body Structure

Response

Simple nervous system

Ganglia

Sense organs

No respiratory system

◦ Diffusion oxygen in, carbon dioxide out

No circulatory system

◦ Nutrients diffuse through internal tissues

No excretory system

◦ Wastes diffuse through internal tissues

Across body wall

Respiration, Circulation and Excretion

Feeding

Parasitic worms

◦ attach to their host

Free living

◦ use grasping mouthparts to catch and eat

smaller animals

◦ Algae or bacteria

Digestive System

Simple digestive system containing a mouth

leading to a short, muscular pharynx that the

nematode uses to suck in food.

The intestine is made of one layer of cells for

absorption of food. The parasitic nematode

intestines do not contain any digestive gland

cells to create enzyme to breakdown food.

Why?

At the end of the intestine, it opens up to the

anus near the posterior tip for excretion of

unabsorbed food.

Digestive System

Nervous System

Simple

Consists of a ring of nervous tissue around the pharynx

called Nerve Ganglion (simple brain) AND nerve tissue

running down the length of the nematode on the dorsal

and ventral trunk.

Reproductive System

Sexes are separate – males are usually smaller

than females

Each consists of a long tube (single in a male,

paired in a female) – which coils back and forth in

the body space

Reproductive System

Female Reproductive System

Paired long tube coils back and forth

in the body space

The two ovaries are long and slender

and widens into two large tubes (the

uterus) where the eggs accumulate.

The uteruses unite into one short

duct (the vagina)

Male Reproductive System

The male’s testis consist of a long

coiled tube were the sperm are

formed.

It gradually enlarges into the

sperm duct, which opens near the

posterior end.

The sperm is transferred to the

female with the aid of a pair of

bristles.

Parasitic Round Worms

Ascaris

One of the most common intestinal

parasites in humans -- over 1 billion

people have it

Lives in small intestine but travels through

the body as a juvenile

Ascaris

Hookworm (Ancylostoma) Hookworm

Human hookworm (Necator sp.) feeds on blood

from inside of intestine

A single worm can drain 20 ml of blood per day

Most serious in children as can lead to physical

and mental retardation

Enters as “Itch worm” between toes

Pinworm (Enterobius)

Lives in lower bowel

Female migrates out anus each night to lay eggs

Secretes irritating toxin to get person to scratch

Re-infection is oral

Trichinella

A serious infection that humans can

contract when eating rare pork containing

encystedTrichinella larvae

Invades selected muscles forming painful

cysts

Causes Trichanosis

Trichinella

Filarial Worms

Is a parasite of dogs

Live in the heart and arteries

Filarial Worms

In humans, the filarial worm causes

elephantiasis

Restricted to the tropical areas of Africa

Uses mosquitos as a secondary host

Adult worms reside in the lymph vessels

which impedes the movement of fluids

causing swelling

Elephantiasis

Guinea Stick Worm

(Dracunculus) In Africa only

Enters while a person is in contaminated

water and burrows through skin and

grows

No cure - is removed by wrapping around

a stick - one turn per day

Contains deadly toxin if broken it can kill

its victim

New Guinea worm