1. Arthropods and Echinoderms
Life Science
Chapter 11

2. Arthropods
The phylum of invertebrates that contains the largest number of different species is Arthropoda.
More than 1,000,000 species have been described by scientists.
Arthropods live in the air, in the water, and on land.
Arthropods are also our main competitors for food.

3. Characteristics of Arthropods
All arthropods share three characteristics:
Exoskeleton: a rigid outer covering that must be shed as an animal grows by a process called molting
Segmented Body: body made of multiple segments
Jointed Appendages: includes legs, claws, wings and antennae

4. Other Characteristics
Arthropods have an open circulatory system, in which blood is not contained within tubes.
The blood is pumped by a heart through out the spaces in the arthropod’s body.
An arthropod’s blood carries food, but it does not carry oxygen.
Oxygen is carried to cells by either gills, book lungs, or a system of air tubes.

5. Reproduction in Arthropods
Arthropods reproduce sexually.
They have both a male and a female parent.
The male produces sperm and the female produces eggs.
In most arthropods, the sperm and egg unite inside the body of the female.

6. Crustaceans
A crustacean is an arthropod that has a hard exoskeleton, two pairs of antennae, and mouth parts used for crushing and grinding food.
Examples of crustaceans include: crabs, lobsters, barnacles and shrimp.

7. The Body of Crustaceans
The body of a crustacean is divided into segments.
A pair of appendages attaches to each segment.
Some have claws and/or walking legs.
Other crustaceans are able to regenerate body parts.
Most crustaceans live in watery environments and obtain oxygen from water using gills.

9. Centipedes and Millipedes
Centipedes and millipedes are arthropods that have many legs.
Centipedes have one pair of legs on each segment.
Millipedes have two pairs of legs on each segment.

10. Millipedes Millipedes live on plants and are shy creatures.
They do not have claws.
Millipedes also are not waterproof and are usually found in damp places under rocks and in soil.

11. Centipedes Centipedes are carnivores that actively hunt their prey.
Centipedes are able to inject poison into their prey through their claws.
Centipedes also are not waterproof and thus must live in damp areas.

12. Spiders Spiders belong to a group of arthropods called arachnids.
Arachnids also include: scorpions, ticks, and mites.
The body of an arachnid is divided into two parts: a head and chest part and an abdomen part.
All arachnids also have eight legs.

13. Spider’s Characteristics
Spiders usually feed on insects.
Spiders can catch their prey using a variety of methods including their webs, hiding places, and venom or poison.
Spiders usually get their oxygen by means of respiratory organs called book lungs because most spiders live on land.

14. Scorpions Scorpions are generally found in dry, desert areas.
Scorpions are most active at night and hide out in the shade during the day.
When scorpions capture their prey, they hold it with their large claws and inject venom into it with the stingers in their tails.

15. Ticks & Mites
Ticks and mites live on other organisms and therefore are considered parasites.
Ticks and mites live by sucking juices out of other living things such as plants and animals.
Ticks can spread diseases such as Rocky Mountain spotted fever and Lyme disease.

16. Insects The largest group of arthropods are the insects.
There are more species of insects than of all other groups combined.
There may be as many as 300 million insects for every person on Earth.

17. Insect Characteristics
Insects are described as having a body that is divided into three parts:
A head
A chest
An abdomen
They also have three pairs of legs attached to the chest part.

18. Insect Structure Insects also have compound and simple eyes.
A simple eye can only detect light and dark.
A compound eye can distinguish colors and detect movement.
Most insects also have wings, normally two pairs of wings.
Insects also use a series of tubes to get oxygen through their exoskeleton and into their body cavity.

19. Growth and Development of Insects: Metamorphosis
Insects grow rapidly and shed their exoskeletons as they get larger.
The growth process of insects is called metamorphosis and involves several stages of development.
There are two types of metamorphosis: complete and incomplete.

20. Complete Metamorphosis
During complete metamorphosis, insects pass through a four stage process.
The first stage produces an egg.
The second stage occurs when the egg hatches into a larva
The third stage occurs as the larva grows into a pupa which are sometimes contained in a cocoon.
The fourth stage is the adult stage

22. Incomplete Metamorphosis
During incomplete metamorphosis, young animals look very much like the adults hatch from eggs.
The young animals however often do not have the organs and wings of the adult stage.
As the young animal grows, it continues molting and getting larger until it reaches the adult size.

23. Insect Behavior Most insects live alone except to reproduce.
Insects signal they are ready to reproduce using a variety of ways including: buzzing, using light, releasing scents, and other behavior.
Social insects, are insects which cannot survive alone and form colonies or hives.
Each individual performs specific tasks for the colony in order for all the animals to survive.

24. Defense Mechanisms of Insects
Insects have many defense mechanisms that enable them to survive.
Wasps and bees use stingers.
Some insects have camouflage to blend with their surroundings.

25. Echinoderms
Echinoderms include starfishes, sea lilies, feather stars, sea urchins, and sand dollars.
These invertebrates are called the spiny-skinned animals.
An echinoderm’s structure includes: an internal skeleton, a five-part body, a water vascular system, and structures called tube feet.

26. Structure of Echinoderms
An echinoderm’s internal skeleton is made of bony like plates of calcium that are bumpy or spiny.
The water vascular system is a system of fluid-filled tubes that carry food and oxygen, remove wastes and help echinoderms move.
The tubes open to the outside through a strainer like structure.
Other tubes connect to suction-cup like tube feet.
Echinoderms use their tube-feet to walk and get food.

28. Starfish
Starfish are not actually fish, however they are shaped like stars.
They have five or more arms that extend from around a central body.
On the underside of the arms are hundreds of tube feet that act as suction cups.

29. Starfish Predatory Skills
When a starfish passes over a clam, it uses its tiny tube feet to grasp the shell.
The suction action of the hundreds of tube feet is used to create a tremendous force on the outside of the shell and force it open.
The starfish then eats the clam.
Starfish also have the ability to regenerate from their body parts.

30. Sea Lilies and Feather Stars
Sea lilies and feather stars are the oldest echinoderms and have long feathery arms.
They spend most their time attached to the ocean bottom.
They use their long arms to gather food from the surrounding water.

31. Sea Cucumber Sea cucumbers resemble warty cucumbers.
They have a mouth at one end and an anus at the other end.
They are usually found lying along the ocean floor.
They move along the floor using five rows of tube feet on their body surface to wiggle back and forth.

32. Sea Urchins and Sand Dollars
Sea urchins and sand dollars are round shaped and rayless.
Sand dollars are flat while sea urchins are dome shaped.
Many sea urchins have long spines that can be used for protection.
Some have poisonous sacs that can deliver painful stings.