1. Chapter 28 Arthropods
Section 1
Characteristics of Arthropods

2. What is an Arthropod?
A segmented, coelomate invertebrate animal with bilateral symmetry, an exoskeleton, and jointed structures called appendages

3. What is an Appendage?
An appendage is any structure that grows out of the body of an animal (such as a leg or an antenna)
Arthropods are the earliest known invertebrates to exhibit jointed appendages
These appendages are adapted for many purposes including: sensing, walking, feeding, and mating

4. Why are jointed appendages advantageous?
Allow more flexibility in animals that have hard, rigid exoskeletons
Allow powerful movements of appendages
Allow an appendage to be used in many different ways

5. What is an exoskeleton? A hard, thick outer covering
Made of protein and chitin
Often reinforced with calcium carbonate in aquatic species
Can be continuous over the body or can be made of separate plates held together by hinges

6. What does an exoskeleton do?
Protects and supports inner tissues
Provides places for muscle attachment
Provides protection against water loss when covered by a waxy layer

7. What are the disadvantages of an exoskeleton?
Heavy…weight of the exoskeleton limits the size arthropods
Cannot grow…so they must be periodically shed through the process of molting

8. What happens during molting?
Before molting occurs, a new soft exoskeleton is formed underneath the current one
When the new exoskeleton is ready the animal contracts muscles and takes in water or air causing the animal’s body to swell until the old exoskeleton splits open
The old exoskeleton is shed
The animal’s body gets bigger due to increased blood circulation (and sometimes also due to the animal taking in air)
The new exoskeleton hardens in a larger size leaving room for the animal to grow

9. What happens during molting?
During molting arthropods are vulnerable to predators because they are soft and cannot use the exoskeleton for the bracing of muscles (can’t move)
So, during molting, arthropods have to hide or remain motionless for a few hours or days until their new exoskeleton hardens

10. How often does molting occur?
Most arthropods molt 4 to 7 times before they become adults

11. How are arthropods segmented?
In most arthropods, segments are fused into three body sections – head, thorax, and abdomen
Some arthropods have a head and a fused thorax and abdomen
Some arthropods have an abdomen and a fused head and thorax (called a cephalothorax)
Some arthropods have all three body sections fused together

12. Why are arthropod segments fused?
Fusion of segments protect the arthropod better
However, fusion of segments also limits the movement of the arthropod

13. What type of respiratory structures do arthropods have?
Arthropods need to have efficient respiratory structures that ensure rapid oxygen delivery to cells because active lifestyle of an arthropod requires a high metabolism and a large oxygen demand

14. What type of respiratory structures do arthropods have?
Three types of respiratory structures have evolved in arthropods:
Gills
Tracheal tubes
Book lungs
(*Some arthropods also diffuse air directly across the exoskeleton and body wall but this requires a very thin and permeable exoskeleton)

15. What type of respiratory structures do arthropods have?
Tracheal tubes
Found in most insects
Consist of branching networks of hollow air passages that carry air throughout the body
Details:
Muscles pump air through the tracheal tubes
Air enters and leaves the tracheal tubes through openings on the thorax and abdomen called spiracles

16. What type of respiratory structures do arthropods have?
Book lungs
Found in most spiders and spider relatives
Consist of air-filled chambers that contain leaf-like plates that are stacked or arranged like the pages in a book

17. What type of respiratory structures do arthropods have?
Gills
Found in aquatic arthropods
Extract oxygen from the water and release carbon dioxide into the water

18. What type of senses do arthropods have?
Arthropods have antennae
Stalk-like structures
Detect changes in the environment (such as changes in chemicals, movement, or sound)
Used for sound and odor communication
Antennae sense the odors of pheromones (chemical odor signals) which signal the arthropod to behave in a certain manner

19. What type of senses do arthropods have?
Most arthropods have one pair of large compound eyes and three to eight simple eyes
A simple eye is a visual structure with only one lens that is used for detecting light
A compound eye is a visual structure with many lenses
Each lens contributes a tiny portion to the total image allowing the arthropod to easily detect movements and color

20. What type of nervous systems do arthropods have?
Have well developed nervous systems that process information from sense organs
The nervous system consists of a double ventral nerve cord, an anterior brain, and several fused ganglia that act as control centers for the body section in which they are located

21. What other body systems do arthropods have?
Arthropods have an open circulatory system
A heart pumps blood into vessels that carry the blood away from the heart
Blood then leaves the vessels and goes directly into the tissues
Blood returns to the heart through open body spaces

22. What other body systems do arthropods have?
Arthropods have a complete digestive system with a mouth, stomach, intestine, anus, and various digestive enzyme producing glands
The mouthparts of most arthropods include one pair of jaws called mandibles that are adapted for holding, chewing, sucking, or biting various types of food

23. What other body systems do arthropods have?
Most terrestrial arthropods secrete wastes through Malpighian tubules that are located in the abdomen and empty into the intestine

24. What other body systems do arthropods have?
Arthropods have well developed muscular systems
Muscles are attached to the inner surface of the exoskeleton on both sides of joints

25. How do arthropods reproduce?
Most arthropods have separate males and females and reproduce sexually
Fertilization is usually internal in terrestrial species but is often external in aquatic species
A few species (like barnacles) are hermaphrodites
Some species (such as bees, ants, aphids, and wasps) can reproduce through parthenogenesis which is a type of asexual reproduction in which a new individual develops from an unfertilized egg
Reproductive diversity is one reason there are more arthropod species than all other animal species combined