Bi 11: Chapter
25 Study Guide: Flatworms, Roundworms,
Mollusks & Annelids
1
Chapter 25–1 flatworms & 25-2 Roundworms: Section review
In this section you were introduced to the group of animals known as unsegmented worms. Segmented
worms include Flatworms (Platyhelminthes)
and Roundworms (Nematodes)
.
You learned that flatworms are the simplest animals with bilateral
symmetry. You also learned
that most members of this phylum exhibit enough cephalization to have what is called the head.
You discovered that roundworms are amongst the simplest animals that have a digestive system with two
openings, a
mouth and an
anus . Several parasitic roundworms that cause diseases in
humans were discussed, including
Ascaris
, Trichinella, and hookworms.
Understanding definitions: building vocabulary skills: Each of the statements below describes either
flatworms, roundworms, or both. If the statement describes flatworms, write an F in the blank before the
statement. If the statement describes roundworms, write an R. If the statement describes both, right both
an F and an R.
_FR____ 1. Are invertebrates
__R___ 2. Are members of phylum Nematoda
__F___3. Includes blood flukes
__FR___4. Includes free living and parasitic animals
__F___ 5. Have a digestive system with only one opening
__F___ 6. May have asexual reproduction
__R___ 7. Eliminate undigested waste through the anus
___R__ 8. Includes Ascaris
a.
b.
c.
d.
e.
head
ganglia (‘brain”)
eyespots (ocelli)
pharynx
gastrovascular
cavity
f. ventral nerve
cords
Applying concepts: understanding the main ideas
The body plan of a free-living flatworm is shown at right.
1. Label each letter structure on the diagram.
2. Label the anterior and posterior ends of the worm.
3. What type of symmetry does the body show?
4. What is the purpose of the branches on structure E?
these work as the stomach,
intestines (gastro) and the circulatory system (vascular) system. In this cavity, food is
digested, absorbed and distributed to the neighboring tissues.
5. What evidence does this diagram show of cephalization?
There are ganglia and a
concentration of sensory organs in one area – this is what cephalization means.
6. What is the function of the structure labeled C?
The eyespots (ocelli) detect light
Bi 11: Chapter
25 Study Guide: Flatworms, Roundworms,
Mollusks & Annelids
2
7. What is the function of the structure labeled D? The pharynx is used to suck food into
the gastrovascular cavity when feeding. It can also be used to pin the food, and
digestive juices can be regurgitated out through the pharynx to perform external
digestion if necessary. Finally, undigested wastes can be expelled from the gastro
vascular cavity through the pharynx as well.
Concept mapping: Consider the concepts presented in section 25 – 1 and how you would
organize them into a concept map. Now look at the map for the chapter 25 below. Notice that
the concept map has been started for you. Add the key facts and concepts you feel are
important for section 25 – 1.
Your mind map should include all pertinent information from Chapter 25-1 & 25-2, and it
should be YOUR personal visual review of the content.
Bi 11: Chapter
25 Study Guide: Flatworms, Roundworms,
Mollusks & Annelids
3
Section 25-3: Mollusks
What is a mollusk? In the first part of the section you discovered that a wide diversity of animals are
classified as mollusks. These animals are classified together in one phylum because all show similar
features during early development and all exhibit different forms of the same body plan.
You then explored the wide varied of form and function among mollusks. You also learned about three
classes of mollusks. Gastropods, such as snails and slugs, move by means of a broad, ventral foot;
many have a one-piece shell. Bivalves, such as clams, have two shells that are joined by a hinge .
Cephalopods, such as octopi and nautiluses , have tentacles.
Mollusks affect humans in a variety of ways. Many mollusks are popular as food, and the oyster is not
only important as a food source but as a producer of pearls . Some mollusks also impact negatively on
humans by serving as intermediate hosts for parasites and by doing damage to gardens and crops.
Relating Definitions: Building Vocabulary Skills
Many of the important terms in this section relate to the way mollusks carry out basic life functions.
Listed below are the seven basic functions that animals must carry out in order to survive. Following is a
list of terms from this section. In the blank following each term, write the function or functions that the
term relates to. Some functions may be used more than once, and others may not be used.
Feeding
Excretion
reproduction
respiration
1. Trochophore: Reproduction
2. Foot: movement, feeding
3. Mantle:
Respiration
4. Radula:
Feeding
response
internal transport
movement
5. Open circulatory system: internal transport
6. Nephridia: Excretion
7. Closed Circulatory system: internal transport
8. Gills: Feeding , respiration
Classifying Mollusks: Understanding the Main Ideas
Each of the following statements describes one of the three main classes of mollusks. In the blank before
each statement, write a G if the statement describes the gastropod, a B if the statement describes a
bivalve, and a C if the statement describes a cephalopod.
1.
2.
3.
4.
5.
6.
7.
8.
9.
Scallops are members of this group.
They feed using a structure called a radula.
Sometimes they produce pearls.
The chambered nautilus is a member of this group.
The are highly intelligent; perhaps more than some vertebrates.
They have two shells
Most have small internal shells or no shells at all
Most have a broad, muscular foot located on their stomach.
Most are sessile, but some can move around by flapping their shells
B
G, C
B
C
C
B
C
G
B
Bi 11: Chapter
25 Study Guide: Flatworms, Roundworms,
Mollusks & Annelids
4
Making a diagram: internal structure of a bivalve
A clam is a typical bivalve. The diagram below shows the internal structures of a clam. Us the terms
listed to correctly label the diagram.
Anterior adductor muscle
intestine
stomach
Gill
Ganglion
Nephridium
Anus
Excurrent Siphon
Incurrent Siphon
Heart
Posterior adductor muscle
mouth
Food
Gonad
a. stomach
b.
c.
d.
e.
f.
g.
h.
i.
j.
k.
l.
m.
n.
adductor muscle
mouth
foot
gonad
intestine
gill
incurrent siphon
excurrent siphon
anus
ganglion (“brain”)
adductor muscle
heart
nephridium
Concept mapping
Consider the concepts presented in Section 25-3 and how you would organize them into a concept map.
Now look at the concept map for Chapter 25 at the end of this package. Notice that the concept map has
been started for you. Add the key facts and concepts you fell are important for Section 25-3. When you
have finished the chapter, you will have a completed concept map.
Section 25-4: Annelids
In this section you were introduced to members of the phylum Annelida. These animals, which are also
known as segmented worms, include the familiar earthworm as well as about 9000 other species,
such as sandworms, bloodworms, and leeches.
You learned that annelids are characterized by a long, segmented body and that they live both in water
and on land. By studying in detail the earthworm’s body systems, you learned how annelids carry out
essential life functions.
Annelids are important in many habitats. Small annelids that live in the ocean serve as food for other
organisms. Earthworms and similar annelids are important in soil conditioning . Earthworms also
perform the valuable function of processing nutrients from dead organisms into substances that can be
used by plants .
Bi 11: Chapter
25 Study Guide: Flatworms, Roundworms,
Mollusks & Annelids
5
Applying Concepts: Basic Function in Annelids
Complete each sentence below to describe how the indicated function is carried out by annelids. You
may add additional sentences if you wish.
1. Respiration. Aquatic Annelids typically breathe through gills, whereas land annelids respire
through their skin.
2. Internal Transport: The circulatory system in annelids is a closed system that is organized around
a dorsal blood vessel and a ventral blood vessel. In each body segment are smaller vessels called ring
vessels. In the earthworm and other annelids, several ring vessels are larger than the others and act
as “hearts’ by pumping blood through the system.
3. Excretion: Annelids produce two kinds of wastes. Solid wastes are eliminated through the anus at
the end of the digestive tract. Wastes from cellular metabolism are eliminated by nephridia, which are
simple tube-shaped organs.
4. Response: Annelids have a well-developed nervous system
with a brain at the front end of the
worm. The brain is connected to a pair of ganglia, from which a ventral nerve cord runs the entire
length of the body. Nerves from each segment of the worm enter and leave the nerve cord at a pair of
smaller ganglia.
5. Movement: Muscles in annelid are two types: longitudinal muscles, which run the length of the
body, and circular muscles, which run in circles around the body.
6. Reproduction: Most annelids reproduce sexually. Some species have separate sexes and fertilize
externally, whereas others are hermaphrodites that fertilize internally.
Relating Concepts: Understanding the Main Ideas
Listed in the left column are the major organs that make up the digestive system of the earthworm. Listed
in the right column are words that describe the basic function of each organ. Match each function if the
right column with the corresponding organ in the left column by writing the correct letter in the blank.
1. Intestine
2. Anus
3. Gizzard
4. Crop
5. Esophagus
6. Pharynx
7. Mouth
f.
d.
a.
e.
g.
b.
c.
a. Chops food into small pieces
b. pumps food and soil or grabs prey
c. Entrance for food
d. Eliminates Waste
e. Storage area for food
f. Digests food
g. Passageway for food
Bi 11: Chapter
25 Study Guide: Flatworms, Roundworms,
Mollusks & Annelids
Label the following diagrams of an earthworm.
Side View
a.
b.
c.
d.
e.
f.
g.
h.
i.
j.
k.
l.
m.
n.
anus
crop (for storage)
dorsal blood vessel
pumping ring vessels (heart)
ganglia (brain)
mouth
setae (helps anchor worm in it’s hole)
pharynx (sucks in soil)
ventral nerve cord)
ventral blood vessel
esophagus
Clitellum (produces “cocoon” for fertilized eggs)
intestine
gizzard (for grinding food)
TOP VIEW
a. ganglia (brain)
b. “heart”
c. ovary
d. nephridia
e. dorsal blood vessel
f. intestine
g. gizzard
h. crop
i. seminal vesicles
j. esophagus
k. septa – (between
segments)
l. pharynx
m. mouth
6
Bi 11: Chapter
25 Study Guide: Flatworms, Roundworms,
Mollusks & Annelids
7
Concept Mapping.
Consider the concepts presented in Section 25-4 and how you would organize them into a concept map.
Now look at the concept map for Chapter 25 at the end of this package. Notice that the concept map has
been started for you. Add the key facts and concepts you fell are important for Section 25-4. When you
have finished the chapter, you will have a completed concept map.