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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

Gut Determinate

DEUTEROSTOMES

Radial

Anus Gut

Mesoderm Mouth

Anus Coelom

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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.