BIOL BC2003: WEEK 1
ANIMAL FORM AND FUNCTION
SEPTEMBER 13-17, 2004
Learning objectives:
(1) Be able to identify and differentiate asymmetrical, radial, and bilateral body plans.
(2) Be able to explain different grades of tissue organization (diploblastic and triploblastic grades).
(3) Be able to explain the function(s) of a coelom.
(4) Be able to explain the presumed adaptive significance of different animal body plans.
(5) Know how cnidarians, platyhelminthes, annelids, arthropods, mollusks, echinoderms, and
chordates differ in their body plans.
Thought and discussion questions:

What is — and is not — an animal?

How do the different animal phyla differ from one another?

What is a body plan? Has the number of animal body plans remained constant through
evolutionary time?

What is cephalization? Does it occur in all animals? Why or why not?

What is the function of a coelom? Does it occur in all animals? Why or why not?

What ecological scenarios are well matched for radial and bilateral symmetry?

Why do many animals have larvae? What advantages does having a larva provide?
Textbook reading to do before coming to lab:
633-675.
fall 2004, Lab 1-1
Campbell et al. 6th edition, Pages
LAB OVERVIEW
ANIMAL FORM AND FUNCTION
THE BIG PICTURE:
In lecture and recitation you learned the features that define animals as well as the major
differences among animal lineages. Today in laboratory you will observe major differences in
body organization and development found in the animal kingdom.
In preparation for lab:
Read lab handout.
Read Campbell sections, paying special attention to the figures.
Consider filling out some parts of the worksheets so you can work
more efficiently during lab.
During lab:
First hour (or less if possible):
Worksheet 1: Symmetry
Worksheet 2: Coeloms
Second and third hours:
Dissections of earthworm and crayfish; Worksheet 3
Comparative morphology of arthropods and annelids
Take-home assignments due
At beginning of lab next week:
Completed worksheets 1-3, including drawings and answers to the
questions.
Typed one-page summary sheet answering the question assigned to
your group for the comparative morphology—1 sheet per
group. These summaries will be photocopied for your
classmates, so please make them organized, thorough, and
easy to understand.
Prepare for next week’s lab.
Note that this is a very busy lab, so please try to adhere to the recommended timetable. It would
be easy to get carried away and spend too much time looking at each of the MANY things you
have to look at this week. Please come prepared to lab, complete work efficiently yet
thoroughly, and be prepared to finish the worksheets and assignments at home before coming to
lab next week.
fall 2004, Lab 1-2
BACKGROUND READING
What is an animal body plan or baüplan?
In today’s lab we will reduce the astonishing diversity and complexity of animal structure,
architecture, and function into several basic themes. We will refer to these themes as body plans
or baüplan (German for “blueprint” or “structural plan”). Baüplan is a term that sums up the
architectural composition and functional design of an animal. In order for animals to work,
structures and functions must be compatible, and this constrains the way in which an animal may
be constructed or organized. Today we will focus on some major differences in animal
construction, organization, and development. We will spend most of the time in lab today
comparing the earthworm and the crayfish.
Components of an animal body plan
Today we will focus on six components of animal body plans:
1. Body symmetry: Symmetry refers to the arrangement of body structures relative to some
axis of the body. Animals vary significantly in their patterns of symmetry (See Campbell
6th edition p. 637, Figure 32.5). Some animals don’t have any symmetry at all (they are
asymmetrical, like some sponges of the Phylum Porifera).
Why do different symmetries exist? Do all possible forms of animal symmetry exist
today? Can you think of a type of animal symmetry that does not exist today, or has not
existed in the history of life on earth? Are there ecological advantages associated with
symmetry?
Here are some biological terms that relate to symmetry and will be helpful in your
description of the animals that we study in lab: anterior: the head or mouth end
(superior or cranial in humans); posterior: the tail or anus end, (inferior or caudal in
humans); ventral: the belly surface; dorsal: the back surface; median: toward the
midline axis; lateral: toward the side of the body.
2. Number of primary tissue layers: Animals may lack tissues altogether (e.g., Phylum
Porifera,) develop two primary tissue layers (diploblastic; e.g., Phylum Cnidaria), or
develop three primary tissue layers (triploblastic; e.g., Phylum Mollusca). Additionally,
the number and diversity of tissue types and cell types varies significantly among
different animal groups (See Campbell 6th edition, page 638, Figure 32.6).
What is the advantage of having more cell and tissue types? Does having greater cell and
tissue diversity pose any problems for an organism?
fall 2004, Lab 1-3
3. Presence/absence of a coelom: Some animals have an internal body cavity (coelom)
that is lined with mesoderm (see Campbell et al. 6th edition p. 638, Fig. 32.6). You
should be familiar with the concept of a body cavity because vertebrates in general and
humans in particular have them. The internal space in your body that contains your lungs
is known as the thoracic cavity and the internal space that contains your digestive and
reproductive organs is known as the abdominal cavity. These are chambers of your
coelom.
Of what use is an internal body cavity? If it is useful, why don’t all animals have one?
4. The alignment of cells during cleavage: The zygotes of animals must divide and
multiply in order to produce a new multicellular individual. Cell division (or cleavage) in
coelomate animals occurs either spirally or radially (see Campbell et al. 6th edition, p.
639, Figure 32.7). In spiral cleavage the planes of cell division are diagonal to the
vertical axis of the animal, whereas in radial cleavage the cleavage planes are
perpendicular or parallel to the vertical axis of the animal.
Which animal groups share the same cleavage patterns? What does this suggest about
their evolutionary relationships? What type of cleavage occurs in the human animal?
5. The fate of the blastopore: The names protostome and deuterostome derive from the
differing fate of the initial opening of the digestive tract (the archenteron) in an embryo
(see Campbell et al. 6th edition p. 634, Figure 32.1 and p. 639, Figure 32.7).
In protostomes the initial opening develops into the mouth, and an opening that develops
later becomes the anus. In deuterostomes, the initial opening develops into the anus, and
an opening that develops later becomes the mouth. Spiral cleavage is characteristic of
protostomes and radial cleavage is characteristic of deuterostomes.
Which animal groups are protostomes and deuterostomes? Why is this important?
6. Skeletal system: We may classify animal skeletons in a variety of ways depending on
their position in the body, their function, and their structure. The three main types of
skeletons that we will be observing today are hydrostatic skeletons, exoskeletons, and
endoskeletons.
How do these skeletal types differ in position, structure, and function? Why do different
animals have different skeletal types and construction? Are some skeletal designs better
than others in certain ecological contexts?
fall 2004, Lab 1-4
Earthworm (Phylum Annelida) cross section
© Jon. G. Houseman, Department of Biology, University of Ottawa
Planaria (Phylum Platyhelminthes) cross section
fall 2004, Lab 1-5
Name __________________________ Day/Time/Instructor__________________________________
BC Bio 2003
Fall 2004
LAB 1, WORKSHEET 1: ANIMAL SYMMETRY
Today you will compare and describe symmetry patterns in four animal specimens, members of the
following phyla:
1) Phylum Mollusca, clam (other mollusks include chitons, snails, slugs, mussels, scallops, oysters,
squids, octopuses, and nautiluses, see pages 656-659 in Campbell);
2) Phylum Brachiopoda, brachiopod (common name, lamp shell, see page 655 that includes crucial
information on its pattern of symmetry—you will want to take note of this before coming to lab);
3) Phylum Echinodermata, Pluteus larva (common name, sea urchin, other echinoderms include sea stars,
brittle stars, sea cucumbers, and sea lilies, see pages 672-674; and
4) Phylum Cnidaria, Metridium (common name, sea anemone; other cnidarians include hydras, jelly fish
{not fish at all}, sea nettles, and corals, see pages 648-650).
It will be very helpful for you to review the pages suggested above, your lecture notes, and your recitation
notes BEFORE coming to lab. This will make your time during lab more productive.
A. First, draw a phylogenetic tree in the space below, showing the evolutionary relationships of these
four phyla, also including the phyla Platyhelminthes, Annelida, and Arthropoda. You will need to
refer to your textbook (and you may want to do this BEFORE coming to lab). On your diagram,
make clear the defining characteristics of each phylum (what makes it different from all the other
phyla).
fall 2004, Lab 1-6
B.
1.
2.
3.
4.
Observe the overall size, shape, and symmetry of your specimens.
Sketch the overall structure of these specimens in the boxes below.
Illustrate the planes of symmetry in these organisms
Designate the type (or types) of symmetry (e.g., bilateral, radial, asymmetrical) present in
these specimens (as in Figure 32.5 on page 637).
5. Finally, answer the questions on the next page based on your observations.
Where possible, draw a scale on your sketches so that the size of your organisms can be determined from
your drawing.
Clam
Brachiopod
type(s) of symmetry :
type(s) of symmetry :
Pluteus larva
Metridium
(this is a prepared slide ; review the microscope
instructions before using for the first time)
type(s) of symmetry :
type(s) of symmetry :
fall 2004, Lab 1-7
C. In adulthood, Echinoderms are considered to have pentameral symmetry, a specific type of radial
symmetry (to see an example, observe a starfish in lab). What type of symmetry is present in the
echinoderm larva that you examined?
D. What hypotheses can you propose to explain why the same organism might have two different types
of symmetry during its lifetime?
E. Are the types of symmetry and the planes of symmetry in the bivalve and the brachiopod the same?
(Don’t forget to refer to the information on page 655 of your textbook.) If not, how do they differ?
F. What type of symmetry is present in the Cnidarian genus Metridium? Can you think of a functional or
ecological explanation for similar symmetry patterns in an adult starfish and in Metridium (you may
need to be creative in thinking about the lifestyle of these organisms and the dangers they encounter in
their environments)?
fall 2004, Lab 1-8
Name____________________________Day/Time/Instructor__________________________________
BC Bio 2003
Fall 2004
LAB 1, WORKSHEET 2: STRUCTURE AND FUNCTION OF THE COELOM
The coelom, or body cavity, is a central feature of many animals (including humans). Examine a slide of
a planarian (Phylum Platyhelminthes) and an earthworm (Phylum Annelida) in cross section. Draw a
simplified sketch of the main structural organization of these two organisms (use the figures in your lab
manual to help identify the structures you observe). Note the presence and location of the coelom (if
present) as well as other major structures, such as the digestive tract (if present), blood vessels (if
present), and nerve cord (if present). Remember to draw neatly in pencil and to label what you see.
Always label the magnification level (multiplying the ocular and objective magnifications). Then, answer
the questions on the next page.
Planarian cross section
Total magnification________
*Remember to calculate
the total magnification
using both the ocular and
objective magnifications.
Earthworm cross section
Total magnification________
fall 2004, Lab 1-9
LAB 1, WORKSHEET 2: STRUCTURE AND FUNCTION OF THE COELOM
1. Which, if any, of these organisms have a coelom?
2. What structures are present within the coelom of the organism(s) you studied? What
structures are present in your (own personal) coelom.
3. What are the functions of the coelom? Are the functions the same for the taxon(a) you studied
as well as for yourself?
4. Develop a hypothesis that might explain why some animals don’t have coeloms.
fall 2004, Lab 1-10
COMPARATIVE ANATOMY OF BILATERIAN PROTOSTOMES:
Annelida and Arthropoda
Phylum Annelida and Phylum Arthropoda:
Do the same biological problems (e.g., obtaining food, moving, and reproducing) result in the
same structural and functional solutions in different phyla? Why or why not? We will focus on
seven biological problems that animals need to solve in order to survive and reproduce: 1)
structural organization and specialization; 2) movement and support; 3) gas exchange; 4)
circulation; 5) feeding and digestion; 6) nervous systems; and 7) reproduction. We will focus our
investigation on two taxa: the earthworm Lumbricus from the Phylum Annelida and the crayfish
Cambarus from the Phylum Arthropoda.
Have annelids and arthropods found the same or different solutions to the above biological
problems? Would a biological “solution” for an annelid “work” for an arthropod? Why or why
not? In cases of difference, can we determine if one structural or functional solution is superior
to another? If so, how? Read the following questions and then proceed with your dissections.
You will then need to revisit these questions and provide answers in a take home assignment.
Group assignment to begin in lab and complete before lab next week:
You will work in groups of 2 or 3 for this assignment. Your group will be assigned ONE of the
topics listed on page 1-12 in the lab manual and will present a summary of the structural and
functional solutions that earthworms and crayfish have found to the biological problems listed in
the lab manual. You should emphasize the morphological differences between taxa as well as
the structural equivalencies between taxa. Additionally, be sure to discuss whether the solution
one organism uses would “work” for the other organism. Finally, comment on whether the
structural/functional solution that one species uses is “better” than the structural/functional
solution that another species uses. There may not be simple answers to these questions. There
may not be a single correct answer to these questions. The goal of this activity is to have you
think about the organisms and how they function, rather than to have you simply memorize their
parts.
As a group, you will turn in ONE typed summary sheet answering the question assigned to your
group for the comparative morphology assignment—ONE-page maximum per group. These
summaries will be photocopied for your classmates, so please make them organized, thorough,
and easy to understand.
At the beginning of lab next week, your group will make a short presentation (5 minutes
maximum) to your labmates explaining the highlights of your topic. Your group may choose to
have one person make the presentation or you may share the presentation responsibilities (but
remember not to go over 5 minutes total).
fall 2004, Lab 1-11
(1) Repetition vs. specialization of body parts. Both annelids and arthropods are segmented
animals; that is, their bodies are divided (either externally and/or internally) into compartments
or units. How do the segments of annelids and arthropods differ? Does one group have more
specialized segments than the other? What data from your specimens support your hypothesis?
Of what advantage is it to have specialized vs. generalized segments? Would Lumbricus benefit
from segment specialization; in other words, could you design a “better” earthworm?
(2) Movement and support. The muscular-skeletal system. Locomotion is a defining feature of
animals. Why do animals move? Many groups of living things do just fine staying in one place.
Animals need to move because they obtain food via heterotrophic ingestion, and food isn’t
always in the same place. How an animal moves depends on where it lives. The earthworm lives
in soil, and the crayfish lives in water. Additionally, how an animal moves depends on its body
construction and skeletal type. What are the differences in skeletal type in the worm and
crayfish? Is the location and distribution of circular and longitudinal muscle different in the
annelid and arthropod? Consequently, how is movement achieved in these very different
muscular-skeletal systems? Is there an advantage to using a lever-based system of appendages
vs. fluid filled chambers? How do earthworms stabilize themselves when they are moving or
trying not to be pulled from soil? Would legs work better in soil? Would setae (present in the
earthworm) work better in water?
(3) Gas exchange. The respiratory system. How do annelids and arthropods obtain oxygen for
cellular metabolism? What structures are present for obtaining oxygen? Is there an advantage to
using gills vs. skin as a means of obtaining oxygen? What are the advantages and disadvantages
of using skin or gills to “breathe”? Is obtaining oxygen more difficult in water or air? Is this
difference reflected in the morphological structures that are used to obtain oxygen in the worm
and crayfish?
(4) Distributing oxygen to the tissues of the body. Circulation system. Do both taxa have hearts?
Blood vessels? Blood sinuses? Blood pigments (like hemoglobin)? How is circulatory fluid
distributed through the body cavity? Describe the differences between earthworm and crayfish
circulatory systems and comment on biological significance of these differences.
(5) Digestive system. Methods of ingestion. Both earthworms and crayfish ingest food particles.
Are there differences in the mouth parts of these taxa? If so, why? Is there an equivalent structure
to the earthworm’s gizzard in the crustacean crayfish? Why are these structures necessary? What
are they equivalent to in the human animal? Is one structure better than the other?
(6) Nervous system. Why are the primary sensory structures located on the anterior portion of the
body in both annelids and arthropods? Is the position of the nerve cord similar in both taxa—
where is it in their bodies? Does it differ from the position of your nerve cord? If so, describe the
differences.
(7)Reproduction. Hermaphroditic vs. separate sexes. Each earthworm has male and female sex
organs, whereas each crayfish is either a male or a female. What are the advantages and
disadvantages of these two different reproductive strategies? Sperm may be stored in the
earthworm (can the crayfish do this?). How does the sperm from a male crayfish reach a female
crayfish? Does internal fertilization occur in the annelids or arthropods we are studying? List
some of the problems and benefits of external fertilization.
fall 2004, Lab 1-12
Earthworm cross section
© Jon. G. Houseman, Department of Biology, University of Ottawa
fall 2004, Lab 1-13
DISSECTION GUIDE FOR ANNELIDS AND ARTHROPODS
You should be able to identify the structures indicated in bold during the lab practical examinations.
PHYLUM ANNELIDA
The name Annelida comes from the Latin word annelus, which means “little ring.” Annelid worms have
the following general characteristics:
 Their bodies are divided into a series of segments. The phenomenon of body segmentation is
commonly is termed metamerism. In annelids, this metamerism is not limited to the external surface,
but includes internal partitions, i.e., circulatory, excretory, nervous, and muscular structures often
show a segmented arrangement.
 They possess a true coelom that separates the gut from the body wall.
 They are soft-bodied and don’t have a hard exoskeleton or endoskeleton.
 They possess a one-way gut, with a mouth at one end and an anus at the other.
 They have a closed circulatory system.
A coelom, or fluid-filled cavity between the body and the gut, occurs throughout Phylum Annelida and in
several other phyla, including Mollusca, Arthropoda, Echinodermata, Hemichordata, and Chordata. It is
likely that the coelom arose multiple times during evolution. In annelids, the coelom partially surrounds
the gut and is a site where gametes and wastes are collected.
Beyond this, the annelids have exploited the coelom as a locomotory structure. The pressure of the fluid
in the coelom is important, because it provides something for the muscles to work against, sometimes
referred to as a hydrostatic skeleton.
One-way flow of material through the gut makes it possible for the gut to become specialized at different
regions ― as the food moves along in one direction, certain portions of the digestive tract can function in
storage, grinding, absorption, etc. The unidirectional gut also allows the organism to keep eating while
digesting and defecating. Efficient digestion of food is important, especially for large, very motile animals
that require large amounts of energy. We will study the digestive system in greater detail next week.
A closed circulatory system is found in both Phylum Annelida and in Subphylum Vertebrata within the
Phylum Chordata. Does this mean that the two phyla are closely related? Why or why not? We will study
circulatory systems in vertebrates during Week Three.
Members of this phylum may be found in marine, freshwater, or terrestrial environments and may be freeliving or parasitic. The Annelida are grouped into three classes: the Polychaeta, Oligochaeta, and
Hirudinea. We will dissect a worm in the genus Lumbrucus, which belongs to Class Oligochaeta. The
name Oligochaeta comes from the Greek words oligos, meaning few, and chaeta meaning bristle.
fall 2004, Lab 1-14
EXTERNAL ANATOMY
Obtain a preserved worm. As you read through this handout, try to locate all the structures labeled on the
diagram on the next page. The body has a pointed, cylindrical anterior end and a flattened posterior end.
Both mouth and anus are terminal, but the mouth is overhung by a lobe, the prostomium. There is no
distinct head.
The ventral side of the worm is paler and slightly flatter than the dorsal side. The dorsal blood vessel is
visible through the body wall. Note the thin non-cellular cuticle that covers the whole body surface. With
a pair of forceps, strip off a small piece of cuticle and examine under the microscope. Look for the pores
through which mucous is discharged from gland cells in the epidermis. Reduce the light if necessary.
There are about 150 wellmarked segments on your
earthworm. Segments 31-37
form a saddle-like clitellum,
swollen glandular region that
secretes a moisture-conserving
cocoon. This structure is
characteristic of oligochaetes.
Feel the minute setae present on
each segment except the first
and last. There are four pairs of
setae positioned ventrolaterally
on each segment. These serve as
anchors while the worm moves
in its burrow or over the ground.
The segments are useful markers for other structures too. Look on the ventrolateral surface for the
location of reproductive openings. Each worm has two pairs of seminal receptacles in the grooves
between segments 9-10 and 10-11, and openings of the oviducts on segment 14. These are both very
small and difficult to see. A pair of prominent “lips” on segment 15 are the openings of the vas deferens
(sperm ducts).
These animals are hermaphoditic but cross-fertilization is the rule. The clitellum of each worm secretes a
slimy tube about itself covering segments 9-36. The anterior ends of two worms are directed in opposite
directions so that the clitellum of one worm (31) is opposite segment 10 of the other worm. Sperm pass
from the sperm ducts (15) posteriorly down the long seminal canals of one worm across to the seminal
receptacles of the other worm (between 9-10 and 10-11). Each worm later produces a cocoon from the
slimy tube. The earthworm produces a 7 mm x 5 mm cocoon containing several eggs, only one of which
develops.
In addition to the mouth, anus, and genital openings, there are paired openings from the nephridia, the
osmoregulatory structures, in all segments except the first three and the last. These are dorsal and anterior
to the setae.
fall 2004, Lab 1-15
INTERNAL ANATOMY:
Place the worm dorsal side
up. At about the 20th
segment, cut into the body
wall to one side of the
dorsal blood vessel. Then
cut anteriorly, pinning
back the body wall as you
go along.
The most conspicuous
structures seen internally
in the earthworm are the
three pairs of seminal
vesicles. These are
attached in segments 9, 11,
and 12 and lie on either
side of the esophagus.
They contain the testes and
sacs in which spermatozoa
mature. Two pairs of
round seminal receptacles
are visible in segments 9
and 10. These store sperm
after copulation.
The body wall is made up
of an outer epidermis, a
thick muscular layer, and a
thin peritoneum. Note the
tube-within-a-tube
arrangement of the body,
with the coelomic cavity
subdivided into
compartments by
intersegmental septa
(singular, septum). At the
anterior end of the alimentary canal, locate the mouth and the muscular pharynx, which is connected to
the body wall by thin strands of muscle tissue. A slender esophagus (segments 6-13) connects the
pharynx to a large thin-walled crop (segments 14-16) used for food storage. The dorsal blood vessel and
five pairs of aortic arches are directly dorsal to the esophagus. Posterior to the crop is a thick-walled
muscular gizzard (segments 17-19) that grinds food. Posterior to the gizzard is the intestine, where
digestion and absorption of food occurs.
The intestine continues posteriorly along the entire length of the body of the worm. View a prepared slide
of a cross-section of the intestine to see the longitudinal dorsal fold, the typhlosole. Immediately ventral
to the ventral blood vessel lie paired solid nerve cords. These give rise to a ganglion and lateral nerve
branches in each segment. Anteriorly, the ventral nerve cords send lateral connectives to two dorsal
cerebral ganglia, the brain, which lie on the anteriormost part of the pharynx.
fall 2004, Lab 1-16
PHYLUM ARTHROPODA
The name “Arthropod” comes from the Greek for “joint” (arthron) and “foot” or appendage (pod). The
phylum Arthropoda is the largest group in the Animal Kingdom, containing more than 75% of all known
species. The phylum includes spiders, ticks, crustaceans, millipedes, centipedes, and insects. In addition
there are many extinct species of arthropods, including trilobites, for this phylum was abundant in the
Cambrian Era about than 550 million years ago. Members are at home in the air, on land, in fresh or salt
water, and as parasites.
Arthropods are similar to annelids in being segmented and bilaterally symmetrical, and in possessing
definite organ systems. In fact, the most derived arthropods, the insects, pass through a larval stage that is
similar in appearance to annelid worms.
Characteristics that distinguish arthropods from annelids are:
 A segmented body, which probably (evolved independently of segmentation in annelids. In addition,
there is often substantial tagmosis, clustering and reduction in number of the body segments, for
more specialized functions.
 A coelom, although one that is quite reduced in size, complexity, and prominence.
 An exoskeleton of chitin, provides protection from dehydration and injury, as well as places for
muscular attachment. However, for growth to be possible, it must be periodically shed in a process
called molting.
 Jointed appendages, specialized for various functions, including locomotion, feeding, copulation.
 They possess a one-way gut, with a mouth at one end and an anus at the other.
 An open circulatory system with blood bathing organs directly in a chamber called a hemocoel; some
large species possess a single-chambered heart.
You will work in pairs to dissect the crayfish, a representative of the Subphylum Crustacea. The
crayfish, Cambarus, is a scavenger that lives on muddy bottoms of streams and ponds. It feeds
nocturnally on worms and dead or decaying matter. Its appendages are differentiated for various purposes.
EXTERNAL ANATOMY
The crayfish body is divided into an anterior
cephalothorax (fused head and thorax) and a
posterior abdomen. The exoskeleton protects the
crayfish from predators, but in order to grow the
crayfish periodically molts. A soft-shell crab is a
crab that has just molted.
The carapace is the part of the exoskeleton that
covers the cephalothorax. It is marked off by
grooves into four areas: an anterior head, a median
cardiac region, and, on each side, two regions that
cover the gills. Lift the lower edge of one side to
expose the feathery gills.
fall 2004, Lab 1-17
On each side of the pointed extension of the head, the rostrum, is a stalked, moveable, compound eye.
Examine the eye with a hand lens or dissecting scope to see the many surface facets. These are separate
eyes and are collectively good for detecting motion. The long antennae and short antennules bear tactile
and chemical sense organs.
Lift the carapace to see the relationship of the legs to the gills.
The abdomen has 5 segments, each with a dorsal plate, a ventral plate, and two lateral plates. The telson
is a post-abdominal ‘tail’ that bears the anus. Uropods flank the telson. To flee quickly from their
enemies, the telson and uropods may be spread like a fan, drawn under the body causing a quick
backward motion of the crayfish.
Males have the same number of abdominal legs as females, but in males the first two pairs are elongated
for sperm transfer. (Be sure to look at both sexes of crayfish.) The first of the walking legs, the cheliped,
is modified for grasping food. The other anterior appendages are modified for sensory or food-tearing or
food filtering purposes.
CIRCULATORY AND DIGESTIVE SYSTEMS: First, locate the mouth and the large mandibles on
either side of it. Then, starting on one side of the carapace, cut into the exoskeleton with a sharp scalpel or
scissors. Carefully remove the dorsal half of the exoskeleton and the gills from each side.
In the mid-dorsal region, locate the diamond-shaped heart. Anterior and to the left and right of the heart is
the large hepatopancreas or digestive gland. The stomach is conspicuous in the anterior part of the
coelom with its horizontal white band delineating the two regions: a large anterior cardiac stomach, in
which food is stored, and a small, almost indistinguishable posterior pyloric stomach. Within the cardiac
chamber is a gastric mill consisting of a set of three pairs of chitinous teeth. Open the cardiac stomach to
see these teeth. Food is ground up here and passed on to the pyloric stomach. Indigestible food is ejected
to the midgut (or intestines) from the pyloric stomach. Smaller particles are passed on to the digestive
glands, where they are digested. Absorption and storage also take place in the digestive glands, the
intestine being lined with cuticle, which hinders absorption. The gonads occupy the body cavity posterior
to the heart and digestive gland. It is difficult to distinguish where the digestive gland ends and the gonad
begins. Finally, locate the anus on the telson. Anterior to the stomach and behind each antenna are
excretory structures, the green glands. External openings are at the bases of the antennae. Draw the
internal structures of the crayfish on the outlines below.
NERVOUS SYSTEM: Examine the brain and nerve cord. The nervous system is similar to that of the
annelids, but better developed. Push the stomach posteriorly and find the esophagus. The dorsal brain is
on the anterior surface of the esophagus, between the green glands. Locate the nerves that connect to the
eyes, antennae, and antennules. The brain is connected to the ventral nerve cord by a pair of nerves that
pass around the esophagus. Trace the ventral nerve cord posteriorly and count the number of ganglia.
Each ganglion gives rise to pairs of nerves that innervate the appendages and internal organs of the
segment in which the ganglion lies, however the first and last are compound ganglia and innervate
multiple appendages.
fall 2004, Lab 1-18
Crayfish outlines for you to label:
fall 2004, Lab 1-19
Name_____________________________Day/Time/Instructor______________________________
BC Bio 2003
Fall 2004
LAB 1, WORKSHEET 3: COMPARISON OF ANNELID AND ARTHROPOD
Comparative Anatomy of Annelids and Arthropods – Digestive Systems
Oneway
or twoway?
Number of
chambers?
What is
organism’s diet?
Noteworthy specializations
Arthropoda
(Crayfish)
Annelida
(Earthworm)
*****Estimate the ratio of digestive system length to body length for each of the organisms.
You will need this information to complete next week’s worksheets.
Comparative Anatomy of Annelids and Arthropods – Body Plans
Symmetry
Tissue grade
Arthropoda
(Crayfish)
Annelida
(Earthworm)
fall 2004, Lab 1-20
Coelom
Development
LAB 1, WORKSHEET 3 continued
Arthropoda
(Crayfish)
Comparative Anatomy of Invertebrates and Vertebrates
Major Tissue or Organ Systems
Repetition or
specialization of
body parts?
System for
movement and
support?
Organs for gas
exchange?
Organs for
circulating O2?
Cephalization;
nerve cord
position?
Hermaphrodite
or separate
male and
female sexes?
fall 2004, Lab 1-21
Annelida
(Earthworm)
GENERAL END-OF-LAB PROCEDURES
You have now finished your first laboratory exercise. However, you are NOT yet ready to leave
the lab. Before you go:
 Look over your worksheets to make certain you have all the information you will need to
complete them at home before handing them in at the beginning of lab next week.
 Remember that there will soon be another section taught in your lab room. Please return
everything to where you found it so that the next students can carry out their labs as
efficiently as possible.
Clean up your lab bench:
o Return materials to where you got them from during lab.
o Dispose of any solutions down the drain (unless specified otherwise). Do not
dispose of solids down the drain; please put them in the trash.
o Throw away any garbage you have generated.


Normal garbage should go in the garbage cans.
ALL dissection waste should go in the containers marked BIOHAZARD
WASTE.
o Place used glassware in labeled containers.
o Rinse off your dissection instruments and trays and return them to the appropriate
locations.
o Wipe off your lab bench and push in your chair.
 If you have any questions regarding the lab or other procedures, please feel free to ask
your instructor or Karolin Rafalski or Margaret Olney in the Biology Laboratory Office
(Altschul 911, 854-2153).
 Don’t forget that each group needs to turn in a summary of the answer to their question
(typed, 1 page maximum) at the beginning of next week’s lab and be prepared to give a
5-minute presentation.
fall 2004, Lab 1-22