This lab introduces students to the hierarchical organization of animal complexity from the cellular level to organ systems. Key concepts covered include the differences between acoelomate, pseudocoelomate, and coelomate organisms. Students learn the three main types of body symmetry - radial, bilateral, and spherical/asymmetrical - and examine examples from the animal kingdom. They also compare the developmental patterns of protostomes and deuterostomes, including differences in cleavage and fate of the blastopore. The lab aims to provide students with terminology to describe positions on bilaterally symmetrical organisms using terms like dorsal, ventral, anterior, posterior, and planes of section.

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General Biology II Lab
Lab #6: Introduction to the Kingdom Animalia
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OBJECTIVES:
1. Understand hierarchical organization of animal complexity.
2. Learn the differences between acoelomate, pseudocoelomate and coelomate organisms.
3. Learn the advantages of cellular specialization to form tissues and organs.
4. Learn how to classify organisms based on body symmetry.
5. Understand the major differences between protostomes and deuterostomes.
6. Learn and employ the directional terms used to identify body positions on different types
of organisms.
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INTRODUCTION:
The multicellular organisms that make up the 32 phyla of Kingdom Animalia have
evolved from the nearly 100 phyla produced during the Cambrian explosion about 600 million
years ago. During this time, an unprecedented variety of novel body plans and architectures arose
(Fig. 1).
Figure 1. Diversity of members belonging to the Animal Kingdom
In the upcoming labs, we will examine the different levels of complexity and organization in
representative phyla of Kingdom Animalia (See Fig. 2). We will consider the environmental

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constraints that led to the evolution of particular body plans and the adaptations that certain
animals evolved in order to survive in their respective environments.
In general, members of Kingdom Animalia are eukaryotic, multicellular, motile (at least
during certain developmental stages), heterotrophic and unlike plants, lack a cell wall.
Additionally, most animals reproduce sexually and have a characteristic pattern of embryonic
development. Similar to alternation of generations observed in previous phyla, organisms in the
Animal kingdom undergo stages of development, starting from the fusion of an egg and a sperm
and ending with a multicellular adult phase. While the morphology of the adult organism is
highly species-specific, the genes that regulate organismal development are often conserved
across species. In addition, the life cycles of members of Kingdom Animalia vary considerably,
i.e., the stages may look completely different from each other (metamorphosis), they may last
for different periods of time (hours vs. years) and can occur in different habitats (e.g. dragonflies
- adults live in air while larvae are aquatic).
Figure 2. Phylogenetic tree of members of Kingdom Animalia
NOTE: Make sure that you fully understand EVERY term used to
characterize animals because these terms will appear again in the
upcoming labs.

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Task 1: Understanding the hierarchical organization of animal complexity
The common descent of animals within Kingdom Animalia can be observed in the
organization of body plans and the fundamental building blocks that all animals share.
Unicellular protozoans, one of the simplest and most ancient groups, limit all their metabolic,
sensory, and reproductive functions to one cell. By varying the organization and specialization of
organelles within this cell, they are able to achieve all the same functions as more structurally
complex organisms.
Protozoans, which display cellular organization, are described as protoplasmic while
multicellular animals (e.g. sponges) characterized by the same cellular level of organization are
collectively referred to as parazoans. In this simplest level of the hierarchy, cells may be
functionally differentiated, i.e. certain sets of cells are devoted to perform a specialized role
within the body. Over time, cellular organization led to the evolution of a cell-tissue level of
organization, where groups of similar cells aggregated into layers (tissues) enabling them to
perform a common function(s). The nerve net in jellyfish (Fig. 14.7 in your dissection atlas) is a
good example of this level of organization.
Following in complexity is the tissue-organ level of organization, produced when
different types of tissues combine to form organs. In general, organs perform more specialized
functions than tissues and can be composed of different tissue types (e.g. the heart, which is
composed of cardiac muscle, epithelial, connective and nervous tissues). This level of
organization is observed exclusively in metazoans, most of which also exhibit an organ-system
level of organization, where multiple organs operate together, forming a system that has a
specific function (Fig. 3). In metazoans, there are eleven organ systems: skeletal, muscular,
integumentary, digestive, respiratory, circulatory, excretory, nervous, endocrine, immune and
reproductive. We will examine some of these systems in greater depth during Labs 8-11.
Figure 3. Hierarchical organization

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The major patterns of organization of animal complexity are described below in Table 1.
As you examine the organisms today, note which level of organization is present in each. Make
sure to sketch the organisms listed for each level of organization, noting the phylum, genus and
species of each.
Table 1
Level of
organization
Protoplasmic Cellular Cell-tissue Tissue-organ Organ-
system
Description All functions
are confined
to a cell
Aggregation
of cells that
are
functionally
differentiated.
Cells are
aggregated into
patters/layers =
tissues.
Different tissues
are organized
into organs;
more
specialized than
tissues.
Organs work
together as a
system to
perform a
coordinated
function
Representative
group
Protista
**not a part
of Kingdom
Animalia.
We will
NOT examine
them today**
Parazoa Radiata Bilateria Bilateria
Example:
a. phylum
b. genus
c. common name
a. Porifera
b. Grantia
c. Sponges
a. Cnidaria
b. Metridium
c. Sea anemone
a. Platyhelminthes
b. Dugesia
c. Planarian
a. Chordata
b. Perca
c. Perch
Drawing of
whole organism
Questions:
1. Can you suggest why, during the evolution of separate animal lineages, there has been a
tendency for complexity to increase when body size increases?

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2. Sponges have folded walls. What advantage could this trait have for the sponge?
3. Could you think of other organisms or organ systems that also have similar folded
structures?
a. What advantages does folding provide for these organisms?
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Task 2: Differentiating between acoelomate and coelomate organisms
A major developmental event in bilaterally symmetrical organisms (see Task 3) was the
development of a fluid filled cavity (coelom) between the outer body wall and the gut (Fig. 14.46
in your dissection atlas). The coelom created a tube-within-tube arrangement allowing space for
visceral organs and an increase in overall body size (Why?). This structure also provides support
and aids in movement/burrowing in some animals. However, not all organisms are coelomates;
some lack a coelom altogether and are called acoelomate (a = without, see Fig. 14.22-14.24 in
your dissection atlas), while others are characterized by a pseudocoelom (pseudo = false, see
Fig. 14.36 and 14.37 in your dissection atlas). All three types of body cavities are illustrated
below in Figure 4.
Figure 4. Types of body cavities

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Examine the organisms listed in Table 2 and complete the missing sections.
Table 2
Sample Organism Acoelomate Pseudocoelomate Coelomate
Phylum Platyhelminthes Nematoda Annelida
Genus Dugesia Ascaris Lumbricus
Common name Flatworms, planaria Roundworms Segmented worms,
Earthworms
Drawing of
Cross section
(slide)
If specimens are
available, dissect
them
longitudinally.
Sketch your
observations in the
space provided.
Questions:
1. Looking at the three representative specimens, what is the main difference between
coelomate, pseudocoelomate and acoelomate organisms?

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2. How are the organs and tissues organized differently in coelomates and acoelomates?
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Task 3: Body plans and symmetry
While the diversity of animal forms is great, the basic body plans can be categorized by
the presence and type of body symmetry (Fig. 5). Symmetry refers to the correspondence in size
and shape between opposite sides of an organism’s body. Sponges, which lack body symmetry,
are considered asymmetrical whereas animals whose bodies are arranged around a central axis
and can be divided by more than two planes along the longitudinal axis exhibit radial symmetry.
This primitive type of symmetry evolved amongst members of phylum Cnidaria (sea anemones,
box jellies, jellyfish and hydra, see Fig 14.7 and 14.16 in your dissection atlas) and Ctenophora
(comb jellies, see Fig. 14.21 in your dissecting atlas). The bodies of the more evolutionarily
advanced bilaterians, in contrast, can be divided into right and left halves along a sagittal plane.
Make sure you understand the basic differences between the three types of symmetry.
Figure 5. Types of symmetry
Compare and contrast the different types of symmetry by examining the animals listed for each
type in Table 3. Answer the questions that follow.

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Table 3
Symmetry type Description Example Phyla/Species
Spherical This symmetry is found in
protozoa. Any plane passing through
the center divides the body into
equivalent/mirrored halves. Best suited
for floating and rolling.
Radiolaria (amoeboid protozoa)
WE WILL NOT EXAMINE THIS
TYPE OF SYMMETRY IN THIS
LAB
Asymmetrical Sponge
Radial Sea anemone
Bilateral Perch
Questions:
1. In what kind of environment would each type of body symmetry would be most efficient?

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2. What is the advantage of having bilateral symmetry? Can any particular task be achieved
more efficiently?
a. Why would this type of symmetry lead to cephalization?
3. Out of all the organisms you examined, is there a particular pattern between the
organisms that have bilateral symmetry? Radial symmetry? Make sure to consider
morphology.
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Task 4: Developmental patterns in bilateral animals: Protostomes vs. Deuterostomes
Bilateral animals follow two major patterns of embryonic development. Based on these
patterns, they are classified as either deuterostomes or protostomes. In deuterostomes, the
blastopore (first embryonic opening) becomes the anus, while in protostomes the blastopore
becomes the mouth. Also, cleavage, the initial process of cell division after a zygote is formed,
differs in the two lineages; in protostomes, cleavage is spiral while in deuterostomes, it is radial
(Fig 6).
The separation of the metazoans (multicellular animals) into two separate lineages,
suggests an evolutionary divergence of the bilateral body plan. This suggests that deuterostomes
and protostomes are separate, monophyletic lineages (See Fig 2).

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Figure 6. Comparison of protostomes and deuterostomes
Examine the animals noted under the “Example species” row in Table 4. Answer the questions
that follow.
PROTOSTOMES
Spiral
Mouth
Mouth
Anus
Coelom
Mesoderm
GutDeterminate
DEUTEROSTOMES
Radial
Anus
Gut
Mesoderm Mouth
AnusCoelom

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Table 4
Protostomes Deuterostomes
Cleavage type Spiral Radial
Blastopore
becomes
Mouth Anus
Representative
Phyla
Platyhelminthes, Arthropoda,
Annelida, Mollusca, Nematoda, and
smaller phyla
Chordata, Echinodermata, and
smaller phyla
Example species Nematoda - Ascaris Sea star – Asterias
Drawing
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Task 5: Describing positions in bilaterally symmetrical animals
For a large portion of this course you will be examining bilaterally symmetrical animals
from various phyla. To be able to locate and refer to specific regions of animal bodies, we will
use terminology listed in Table 5.
Table 5
Term Meaning
dorsal toward the upper surface (back)
ventral toward the lower surface (belly)
anterior; cranial toward the head
posterior; caudal toward the tail
medial toward the midline of the body
proximal toward the end of the appendage nearest the body
lateral toward the side; away from the midline of the body
distal toward the end of the appendage farthest away from the body
frontal plane divides the body into dorsal and ventral halves
transverse plane divides the body into anterior and posterior halves
sagittal plane divides the body into left and right halves

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Figure 7. Planes of sections in a crayfish
In addition to the terms listed in Table 5, different terminology is used to describe
radially symmetrical vs. bilaterally symmetrical animals. These terms are listed in Table 6.
Table 6
As a group, practice using these directional terms to refer to a particular part/portion of
the body. Make sure to use available specimens to practice and to include both radially and
bilaterally symmetrical animals during this exercise.
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Radial Bilateral
Direction Synonyms Direction Synonyms
oral apical anterior rostral, cranial,
cephalic
aboral basal posterior caudal
peripheral — dorsal —
peripheral — ventral —
peripheral — left (lateral) sinister
peripheral — right (lateral) dexter
medial medial
proximal proximal
distal distal
sagittal
plane
frontal
plane
transverse
plane

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Task 6: Body axes charades – Run by your TA
To practice using the correct terminology when referring to different locations on the
body, you will play a game of charades. Your TA will divide the whole class into two groups,
each of which will be given a list of organs/body parts. Each group’s list will be different
therefore make sure that you do not to share your list with members from the other group.
Your group will choose a student from another group to describe one of the words on
your list to his/her group. The student will have 2 minutes to describe the word, using only the
words from the bilateral body axes (see Tables 5 and 6). Note that you cannot use words that
describe the function of the organ/body part. For example, if the organ to be described is the
heart, you are not allowed to say that it pumps blood. Instead, you can say that it is posterior to
the head and is anterior to the belly button. If his/her group can guess the right answer, then that
team gets a point but if they don’t guess correctly, then your team gets the point. Make sure to
alternate the order of the teams guessing.
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LOOK AHEAD:
Before coming to lab next week, make sure to read the Development task sheet.