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ArthropodsChapter 28
Arthropods include:• Insects, Arachnids, Crustaceans, Centipedes
Common characteristics of all arthropods:
1. Invertebrates-no backbone2. Bilateral symmetry- divide
into 2 equal sides at one point3. Coelom- cavity around internal
organs4. Exoskeleton-outside body
skeleton5. Jointed appendages-
structures growing out of body have joints
6. Open circulatory system –blood pools in spaces (not vessels)
Common characteristics cont…
7. Complete digestive system -mouth, intestines, stomach, anus
8. Mandibles-a variety of jaws/
Functions: hold, chew, suck, and bite
Appendages
• Used for 1. locomotion, 2. sensing, 3. feeding, 4. mating
Exoskeleton• Hard thick covering
made of protein & chitin• May be solid all over
body or may be in segments
Functions1. Protect2. Support internal tissues 3. A place of attachment for muscles, prevents 4. Water loss
Exoskeleton growth
• Can’t grow as the body grows
• They must shed the old skeleton & grow a new one/process called molting
• The new skeleton will grow underneath & eventually pop off the old one
• Most arthropods molt 4-7 times in life
Most arthropods have 3 segments to their body
These include:
-The head
-The thorax (chest area)
-The abdomen
How do arthropods breathe (respire)?
1. Aquatic arthropods-use gills ex. Crayfish
Breathing cont…2. Most insects use tracheal tubes
-branching networks of hollow air passages that carry air through body.
-Muscles pump air through the tubes to openings called spiracles.
Ex. grasshopper
Breathing cont…3. Arachnids use
book lungs
-these air chambers are stacked like books
Ex. Spider
Arthropods have acute (very good) senses
1. Quick movement Ex. Fly2. Antennae-use to detect and
communicate3. Pheromones-chemicals
used to signal Ex. Ants4. Acute vision (simple and
compound eyes)-detect motion very well-can see in almost all directions except directly behind.
Ex. This is why it is hard to hit a fly!
Reproduction in Arthropods
• Most have 1 type of sex organ on each (male or female)
• A few are hermaphrodites (male & female organs)
Types of fertilization
-If it lives on land-fertilization is internal
-If it lives in water-fertilization is external in water
Arthropod classification:
• Kingdom: Animalia
• Phylum: Arthropoda
• Classes: 4 classes
4 classes of arthropods
1. Arachnids-spiders, scorpions, mites, ticks
2. Crustaceans-all are aquatic-lobster, shrimp, crayfish
3. Centipedes & millipedes- they differ on the number of legs on each section & the type of food they eat
Class Insecta:• Includes millions
of species (largest group)
• Mate only around 1 time in lifetime
• Eggs are fertilized internally and shells form around the eggs
• Female lays the eggs after they are fertilized
• The # of eggs laid is enormous– Purpose: to
increase chance of survival
Insect cartoon
Changes insects undergo after hatching:
Metamorphosis-series of changes controlled by chemical substances
2 Types of Metamorphosis:
1. Complete metamorphosis-has 4 stages(ex. Butterfly)
4 stages:a. Eggb. larva-free living worm-like stage (caterpillar)c. pupa-larva tissue broken down and replaced in a case-cocoond. adult
Complete metamorphosis:
2. Incomplete metamorphosis -has 3 stages (Ex. Grasshopper)3 stages:a. eggb. nymph-smaller version of adult (looks like adult but lacks appendages like wings and cannot reproducec. adult
Know Insect Structures!• P. 752 Draw and
label the grasshopper
• Write the functions under each labeled part
• Leave in notebook to study for test
• Study drawing, functions and notes for test
