12.3 Lesson 12.3: Arthropods
Lesson Objectives
- Explain what arthropods are.
- Describe the features of crustaceans.
- Describe the characteristics of centipedes and millipedes.
- List the features of arachnids.
- Describe why arthropods are important.
Check Your Understanding
- What is an invertebrate?
- What do mollusks and echinoderms have in common?
Introduction
With over a million described species in the phylum containing arthropods, chances are you
encounter one of these organisms every day, even without leaving your house. As much as
we would like to eliminate all insect pests from our dwellings, for example, there is a great
probability you will see an ant, a spider, a fly, or a moth inside. Even if you don’t, you will
most likely see such creatures in your yard or on a walk around your neighborhood.
Wherever you observe these animals, you will see a tremendous amount of diversity and
adaptations. You will also learn, despite how you feel about how annoying some of these
organisms may be, how beneficial in fact they are both ecologically and economically.
What are Arthropods?
Arthropods belong to the phylumArthropoda, which means “jointed feet,” and includes
four living subphyla. These are chelicerates, including spiders (Figure12.16), mites, scorpi-
ons (Figure12.17) and related organisms; myriapods, comprising centipedes (Figure12.18)
and millipedes (Figure12.19) and their relatives, who are hexapods, including insects and
three small orders of insect-like animals; and crustaceans, including lobsters (Figure12.20),
crabs (Figure12.21), barnacles (Figure12.22), crayfish (Figure12.23), and shrimp.
Arthropods are characterized by the possession of a segmented body with appendages on at
least one segment. Arthropod appendages are used for feeding, sensory reception, defense,
and locomotion. Their heart is on the dorsal side and the nervous system on the ventral.
They are covered by a hard exoskeleton made of chitin, which provides physical protection
and among terrestrial species resistance to drying out. In order to grow, arthropods shed