Chapter 13: Mollusks, Worms, Arthropods, Echinoderms

Mollusks
1. Mollusks are soft-bodied invertebrates that
usually are covered by a hard shell. They
move using a muscular foot.
2. Mollusks with one shell are gastropods.
Bivalves have two shells. Cephalopods have
an internal shell and a foot that is divided
into tentacles.
Segmented Worms
1. Segmented worms have tube-shaped bodies
divided into sections, a body cavity that
holds the internal organs, and bristlelike
structures called setae to help them move.
2. An earthworm’s digestive system has a
mouth, crop, gizzard, intestine, and anus.
Polychaetes are marine worms. Leeches are
parasites that attach to animals and feed on
their blood.
Copy and complete the following concept map about insects.
Three body
regions
Arthropods
1. More than a million species of arthropods
exist, which is more than any other group
of animals. Most arthropods are insects.
2. Arthropods are grouped by number
of body segments and appendages.
Exoskeletons cover, protect, and support
arthropod bodies.
3. Young arthropods develop either by
complete metamorphosis or incomplete
metamorphosis.
Echinoderms
1. Echinoderms have a hard, spiny exoskeleton
covered by a thin epidermis.
2. Most echinoderms have a water-vascular
system that enables them to move,
exchange carbon dioxide and oxygen,
capture food, and give off wastes.
Insects
have
which are including
life.msscience.com/interactive_tutor
Legs
CHAPTER STUDY GUIDE 387
(l)Charles McRae/Visuals Unlimited, (r)Mark Moffet/Minden Pictures