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 to1. List synapomorphies that distinguish animals from all other eukaryotes2. Understand the meanings of asymmetry, radial and bilateral symmetries3. Be able to recognize the major animal phyla on the basis of

a. body symmetryb. embryonic germ layers (ectoderm, endoderm, mesoderm)c. presence or absence of an internal body cavityd. ontogeny and morphology of the internal body cavitye. ontogenetic differences between protostomes and deuterostomes.

4. Be able to recognize acoelomate, pseudocoelomate and coelomate body plans5. Distinguish between

a. spiral and radial cleavageb. determinate and indeterminate cleavagec. schizocoely and enterocoely

A. Ontogenetic and morphological characters present in major animal phyla

Evolutionary relationships among the Animalia are sometimes controversial, and classifications are undergoing constant revision as new molecular data become available. In many cases, the phylogenetic trees based on morphological characters have been completely upended in light of apparent molecular characters thought to be common to monophyletic groups. And even some morphological and ontogenetic characters that have been considered dogma are surprising investigators who have taken a closer look.

For example, it was once believed that only the Spiralian Lophotrochozoans (true flatworms, annelids, mollusks, lophophorates, etc.) underwent spiral

cleavage during embryo development. Radial, indeterminate cleavage has been a hallmark of deuterostome monophyly. But some recent research suggests that not all organisms currently classified as deuterostomes undergo this type of development.

In short, it is sometimes frustrating that various data sets do not always give the same answer. View the phylogenetic tree on the following page. It represents a modern hypothetical phylogeny of animals based on multiple forms of molecular data.(source: http://metazoan.auburn.edu/halanych/lab/Pub.pdfs/Halanych2004.pdf )

Review the list of morphological characters in the table below.

Using a hashmark to indicate where a character first evolves, place the letter of each character in the appropriate location on the phylogenetic tree to indicate where it makes its first evolutionary appearance.

a. lophophore feeding apparatusb. mesoderm lines parietal and visceral surfacesc. body cavity contains acellular mesogloead. coelom formed via enterocoelye. mesoderm derived from endodermf. body cavity contains cellular mesenchymeg. cellular division of laborh. complete digestive systemi. diploblastyj. triploblastyk. coelom formed via schizocoelyl. bilateral symmetrym. radial symmetryn. cnidoblast stinging cellso. true tissuesp. nervous system embryonically dorsalq. blastopore becomes the mouthr. blastopore becomes the anuss. trochophore larvat. pseudocoelom a persistent blastocoel

Pronunciations:cnidoblast – NEE’ - doh – blastcoelom – SEE’ – lomenterocoely – EN’ - ter - oh - see - leelophophore – LOW’- fo-four6

mesogloea – mes - oh – GLEE’ - uhpseudocoelom – SUE’ - doh - see – lomschizocoely – SKIZ’ – oh – see - leeBilateria (bi-luh-TIER’ - ee - uh)Lophotrochozoa (low - fo - tro - ko - ZO’ – uh)Ecdysozoa (eck – dee – so – ZO’ – uh)

1. What does the placement of the characters on the phylogenetic tree imply about evolutionary

relationships among the Bilateria?

2. What does the placement of the characters on the phylogenetic tree imply about evolutionary

relationships among the Lophotrochozoa?

3. What does the placement of the characters on the phylogenetic tree imply about evolutionary

relationships among the Ecdysozoa?

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 Common name protostome/deuterostome/neither

HexactinellidaCalcareaCtenophoraAcoelaCestodaRotiferaPhoronidaBivalviaHemichordataUrochordataHolothuroideaPriapulida

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 Function1. 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 Applications1. 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 d. heartworm (a nematode) g. tapewormsb. ear mites e. ringworm fungus h. ticksc. leeches f. liver flukes i.

caterpillars

2. It turns out that although lufenuron is effective against insects (Arthropoda, Hexapoda), it

does not kill ticks (Arthropoda, Arachnida). Devise multiple, 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 GABA2. 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.

DiscussionCan 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.