Download Animal Form and Function by Dana Krempels

Animal Form and Function by Dana Krempels
Animalia is characterized by a distinct progression of complexity in form and function. Early
in animal evolution, body symmetry, embryonic germ layers, and ontogenetic origins
of major anatomical structures diverge as taxa branch from common ancestors.
Before you begin this workshop, be sure you are able to
1. List synapomorphies that distinguish animals from all other eukaryotes
2. Understand the meanings of asymmetry, radial and bilateral symmetries
3. Be able to recognize the major animal phyla on the basis of
a. body symmetry
b. embryonic germ layers (ectoderm, endoderm, mesoderm)
c. presence or absence of an internal body cavity
d. ontogeny and morphology of the internal body cavity
e. ontogenetic differences between protostomes and deuterostomes.
4. Be able to recognize acoelomate, pseudocoelomate and coelomate body plans
5. Distinguish between
a. spiral and radial cleavage
b. determinate and indeterminate cleavage
c. schizocoely and enterocoely
To review the items above, go to
http://www.bio.miami.edu/dana/160/160S16_15.html
A. Ontogenetic and morphological characters present in major animal phyla
Note the characters in the table below. Each should be placed on the phylogenetic tree (on the
next page) to indicate where it appears in the animals above that character. (Enter only the
letters, since there’s no room to write the entire character description.)
a. lophophore feeding apparatus
b. mesoderm lines parietal side of body wall
c. body cavity contains acellular mesogloea
d. coelom formed via enterocoely
e. mesoderm derived from endoderm
f. body cavity contains cellular mesenchyme
g. cellular division of labor
h. complete digestive system
i. diploblasty
j. triploblasty
Pronunciations:
cnidoblast – NEE’ - doh – blast
coelom – SEE’ – lom
enterocoely – EN’ - ter - oh - see - lee
lophophore – LOW’- fo-four
mesogloea – mes - oh – GLEE’ - uh
pseudocoelom – SUE’ - doh - see – lom
schizocoely – SKIZ’ – oh – see - lee
k. coelom formed via schizocoely
l. bilateral symmetry
m. radial symmetry
n. cnidoblast stinging cells
o. true tissues
p. nervous system embryonically dorsal
q. blastopore becomes the mouth
r. blastopore becomes the anus
s. trochophore larva
t. pseudocoelom a persistent blastocoel
1. What does the placement of the characters on the phylogenetic tree imply about evolutionary
relationships among the Bilateria (bi-luh-TIER’ - ee - uh)?
2. What does the placement of the characters on the phylogenetic tree imply about evolutionary
relationships among the Lophotrochozoa (low - fo - tro - ko - ZO’ – uh)?
3. What does the placement of the characters on the phylogenetic tree imply about evolutionary
relationships among the Ecdysozoa (eck – dee – so – ZO’ – uh)?
4. Do a Google Image Search of the name each of the following taxa and view
photos/videos of them. What is the common name for animals in each of these phyla? For
each, indicate whether it is a protostome, deuterostome, or neither.
Taxon Name
Hexactinellida
Calcarea
Ctenophora
Acoela
Cestoda
Rotifera
Phoronida
Bivalvia
Hemichordata
Urochordata
Holothuroidea
Priapulida
Common name
protostome/deuterostome/neither
4. Do another search. List some familiar examples of organisms in each of the following taxa:
Anthozoa (Cnidaria)
Cestoda (Platyhelminthes)
Cephalopoda (Mollusca)
Annelida
Nematoda
Hexapoda (Arthropoda)
Arachnida (Arthropoda)
B. Ancestry, Form and Function
1. Consider the synapomorphies common to both protostomes and deuterostomes.
Based on this information, what do you think the most recent common ancestor of these
organisms might have looked like? What characters did it have?
2. Based on your description of the protostome/deuterostome common ancestor, which organ
system(s) in these animals are likely the most primitive? (i.e., which evolved first?)
3. Consider the synapomorphies common to all Ecdysozoans. Based on this information,
what do you think the most recent common ancestor of these organisms might have looked
like? What characters did it have?
4. Consider the synapomorphies common to all Lophotrochozoans. Based on this
information, what do you think the most recent common ancestor of these organisms might
have looked like? What characters did it have?
5. List synapomorphies that set animals in each of the following taxa apart from the ancestral
Ecdysozoan (and from each other).
a. Nematoda
b. Arthropoda
6. How does the main body cavity of a nematode differ from that of an arthropod?
List at least three key features.
7. List synapomorphies that set animals in each of the following taxa apart from the ancestral
Lophotrochozoan (and from each other).
a. Mollusca
b. Annelida
8. Both Mollusks and Arthropods have (1) an open circulatory system and (2) a reduced
coelom that functions as the pericardium (pear-ee-KAR’-dee-um) and gonocoel
(GONE’-oh-seal). If the hypothetical relationships in the tree above are correct, what does
this suggest about the evolution of these two characters in these distantly related phyla?
a. What defines a true coelom?
b. What is a pericardium?
c. What is a gonocoel?
9. Consider the synapomorphies common to all Deuterostomes. Based on this
information, what do you think the most recent common ancestor of these organisms might
have looked like? What characters did it have?
10. List synapomorphies that set animals in each of the following taxa apart from the ancestral
Deuterostome (and from each other).
a. Echinodermata
b. Hemichordata
c. Chordata
C. Practical Applications
1. A drug called lufenuron (loo-FEN’-yur-on) interferes with the activity of an enzyme known
as chitinase (KAI’-tin-ayze), which is involved in the normal formation of chitin (KAI-tin) in
growing arthropods. Lufenuron prevents normal maturation of animals that use chitin as
structural support, such as in the exoskeleton (arthropods) or a protective cuticle
(nematodes) surrounding the skin. Which of the following do you think would most likely be
adversely affected by medicating an infected host mammal with lufenuron?
a. fleas
b. ear mites
c. leeches
d. heartworm (a nematode)
e. ringworm fungus
f. liver flukes
g. tapeworms
h. ticks
i. caterpillars
2. It turns out that although lufenuron is effective against insects (Arthropoda, Hexapoda), it
does not kill ticks (Arthropoda, Arachnida).
Devise one or more logical hypotheses that might explain this.
3. Animal phyla have long been classified into putatively monophyletic assemblages on the
basis of their body plans. However, as more sophisticated molecular techniques (nucleic acid
sequencing) have been applied to systematics, it has been discovered that shared
morphological characters do not always reflect recent common ancestry.
View the phylogenetic trees below.
Phylogeny based on morphology
Phylogeny based on molecular data
Now consider the following:
Ivermectin (EYE’-ver-mek-tin) is a macrolide (MAK’-ro-lide) drug produced from a
fungus (Streptomyces avermitilis) first isolated from a soil sample in Japan. Ivermectin is an
agonist for the neurotransmitter gamma-aminobutyric acid (GABA), a major
inhibitory neurotransmitter.
(NOTE:
an agonist increases the effects of the
neurotransmitter, whereas an antagonist reduces the effects.)
In mammals, GABA-containing neurons and receptors are found in the Central Nervous
System. In arthropods and nematodes GABA is found primarily in the Peripheral Nervous
System. This difference in location of GABA receptors is one reason why ivermectin can be
safely administered to (most) mammals for treatment of arthropod and nematode parasites.
Here’s how ivermectin works:
1. Ivermectin binds to a neuronal membrane, increasing release of GABA
2. GABA binds to the GABA-receptor-chloride channel complex of the postsynaptic
neuronal membrane. (Nerve impulses travel from the presynaptic neuron, across the
synapse to the postsynaptic neuron.)
3. The binding of ivermectin to the receptor complex causes an influx of chloride ions.
4. The abnormal influx of chloride ions hyperpolarizes the neuronal membrane.
5. The membrane becomes less excitatory
6. Nerve impulse transmission is decreased.
The hyperpolarization of neuronal membranes causes a fatal flaccid paralysis (FLA’-sid,
meaning floppy or loose, as opposed to paralysis caused by permanently contracted muscles)
in arthropods and nematodes.
Discuss the implications of this response to ivermectin in both arthropods and nematodes. Do
you think it is evidence of convergent evolution, or of homology? Explain your answer.
Discussion
Can you think of other examples of characteristics used to devise phylogenies that might also
have relevance in treatment of disease, solution of environmental problems, or other practical
applications? Discuss.