February 12, 2018

Biology: Worms

What Worms Have in Common

Source: Modern Farmer
The three major groups of worms are: flatworms, roundworms, and segmented worms.
All worms are invertebrates, and they all have long, narrow bodies without legs.
All worms have tissues, organs, and organ systems.
All worms have bilateral symmetry.

Response to the Environment

Worms are the simplest organisms with a brain, which is a knot of nerve tissue located in the head end.


Both sexual and asexual reproduction are found in worms. In other species each individual has both male and female sex organs.
Many worms reproduce asexually, for example by breaking into pieces.
Ability to regrow body parts is called regeneration.


Source: One World One Ocean
Most flatworms are parasites that obtain their food from their hosts. A parasite is an organism that lives inside or on another organism. The parasite takes its food from the organism in or on which it lives.


A tapeworm's body is adapted to absorbing food from the host's digestive system.


Some flatworms are nonparasitic, or free-living.
Planarians, are scavengers.
But they are also predators and will attack any animal smaller than they are.


Source: NHS Choices
Roundworms have cylindrical bodies. Their bodies thrashing from side to side.
Many roundworms are carnivores or herbivores, others are parasites.
Roundworms have a digestive system that is like a tube, open at both ends.

Segmented Worms

Since their bodies are long and narrow, some segmented worms look a bit like flatworms and roundworms.


Earthworms and other segmented worms have bodies made up of many linked sections called segments.
Like roundworms, earthworms have a one-way digestive system with two openings.

A Closed Circulatory System

Segmented worms have a closed circulatory system.
A closed circulatory system can move blood around an animal's body much more quickly than an open circulatory system can. Blood quickly carries oxygen and food to cells.
An animal with a closed circulatory system can be larger and more active than one with an open circulatory system.

How Earthworms Live

If a worm dries out, it will die, because it obtains oxygen through moisture on its skin.
Well-developed muscles let an earthworm move through its burrow.