Lecture 15: Introduction to Animals

Question 1

How many animals exist on our planet today and what did they originate from?

Answer 1

3million to 10 million animals exist.
Animals originated from single-celled eukaryotes.

• Choanoflagellates are the closest living relatives to animals. A common ancestor is shared 900 million years ago.

Question 2

What key traits do the monophyletic clade ANIMALS form? (4)

Answer 2

1. All are multicellular eukaryotes with no cell wall but have an extensive extracellular matrix.
2. Heterotrophs
3. Move under own power at some point in life cycle (locomotion)
4. All animals other than sponges have neurons that transmit electrical signals to other cells and muscle cells that change body shape by contracting

Question 3

What techniques prove that animals are monophyletic group? What is the most ancient lineage of animals?

Answer 3

All animals have a single common ancestor that was multicellular
Monophyleticism proved by:
- fossils
- comparative morphology
- comparative development
- comparative genomics

Sponges are the most ancient lineage of animals

Question 4

Define:
1. Fossils
2. Comparative morphology
3. comparative development
4. Comparative genomics

Answer 4

1. Fossils are the remains of old species
2. Comparative morphology provides information about which characteristics are used to define fundamental architecture
3. Comparative development provides information about patterns of gene expression and morphological change
4. Comparative genomics provides information about the relative similarity of genes or whole genomes of diverse organisms

Question 5

Are sponges monophyletic or paraphyletic?
What is the basic genetic tool kit for multicellularity in sponges?
What do sponges have in place of complex tissue?
Some sponges have true epithelium, what is this?

Answer 5

1. Sponges are paraphyletic
2. Cell-cell adhesion, Cell-ECM adhesion, Few even have epithelium
3. Sponges have groups of similar cells that are organized into tightly integrated structural and functional units
4. Epithelium is a layer of tightly joined cells that covers interior and exterior surface of animal. It is essential to animal form and function.

Question 6

What is the sponges first hypothesis?

Answer 6

• Earliest animals to appear in the fossil record
• First sponges appeared more than 700mya ago
• The basal position of sponges on the phylogeny is proven by the presence of multicellular sponges and absence of fossils of other multicellular organisms

Question 7

What characteristics do sponges share with choanoflagellates? (5)

Answer 7

• Both are benthic (live at bottom of aquatic environments) and sesile (adults live permanently attached to substrate)
• Both feed using cells with nearly identical morphology
• Beating flagella of choanoflagellates and choanocytes in sponges trap organic debris
• Feeding occurs at cellular level
• Choanoflagellates sometimes form colonies and sponges were once considered colonies of single-celled protists

Question 8

How do sponges differ from choanoflagellates?

Answer 8

Sponges contain many specialized cell types that are dependent on each other. Some of these cells occur in organized layers surrounded by extracellular matrix (ECM).

Question 9

What is a diploblast? What are the two germ layers?

Answer 9

A diploblast is an animal whose embryos have two types of tissues.
The ectoderm (“outside-skin”)
The endoderm (“inside-skin”)j

These two layers are connected by a gelatinous material called the mesoglea.

Question 10

What is a triploblast?

What do the three layers become?

Answer 10

Triploblasts have three germ layers that develop into distinct adult tissues and organs.

Ectoderm: Skin and CNS
Mesoderm: circulatory system, muscle, internal structures such as bone
Endoderm: lining of digestive tract and organs that connect to it

Question 11

What features are shared between diploblasts and triploblasts?

Answer 11

Both have:
- medoerm like cells in mesoglea
- genes coding for structural components of mesodermal cells
- some can change the shape of their bodies
- actin & myosin

Question 12

What is different about diploblasts compared to triploblasts?

Answer 12

Diploblasts are missing:
- mesodermal specification genes
- well defined mesoderm
- true muscles

Question 13

What is body symmetry? Radial symmetry vs bilateral?

Answer 13

Body symmetry is the key morphological aspect of an animal’s body plan.

Radial symmetry ->
- Cnidarians, ctenophores, sponges have this
- At least two planes of symmetry
- Evolved independently in the echinoderms

Bilateral symmetry ->
- most other animals have bilateral
- single plane of symmetry and long narrow bodies

radial symmetry evolved earlier than bilateral

Question 14

Are cnidarians (jellyfish) radially or bilaterally symmetric?

Answer 14

Cnidarians are bilaterally symmetric but appear to be radially symmetric. This is especially true of many species of sea anemone.

Question 15

What is a bilaterian? Where does their symmetry come from?

Answer 15

A bilaterian is a triploblastic, bilaterally symmetric animal.
The symmetry is a result of:
- Hox genes: regulate development of anterior-posterior axis
- Decapentaplegic (dpp) genes: regulate development of dorsal-ventral axis

Question 16

What data supports the hypothesis that cnidarians and bilaterians convergently evolved bilateral symmetry?

Answer 16

• Some parts of genetic tool kit for bilateral symmetry arose before cnidarian and bilaterian lineages split
• Other parts evolved after the lineages split

Question 17

What is the function of neurons and the nervous system?
What is the nerve net?

Answer 17

• Transmit and process information in the form of electrical signals
• Radially symmetrical cnidarians and ctenophores have nerce cells that are organized into a nerve net

Question 18

What is cephalization?

Answer 18

Cephalization is the evolution of the head where structures for feeding, sensing environment, and processing information are concentrated.

Bilaterally symmetric organisms tend to encounter things at one end

Question 19

What is cephalization?

Answer 19

Cephalization is the evolution of the head where structures for feeding, sensing environment, and processing information are concentrated.

Bilaterally symmetric organisms tend to encounter things at one end

Question 20

Define the tube-within-a-tube body plan of bilaterians.

Answer 20

Looks like a tube within a tube
Inner Tube: Gut with a mouth on one end and anus at other
Outer tube: forms nervous system and skin
Mesoderm: forms muscles and organs

Outer tube and inner tube are ectoderm and mesoderm

Question 21

What is a coelom?

Answer 21

A coelom is an enclosed, fluid-filled body cavity between the tubes.
-Provides space for oxygen and nutrients to circulate
enables organs to move independently of each tother

Question 22

What is a true coelomate? Acoelomate? Psuedocoelomate?

Answer 22

A true coelomate has a coelom completely lined with mesoderm.

An acoelomate has no coelom, such as flatworms.

A pseudocoelomate has a coelom only partially lined with mesoderm, such as roundworms and rotifera.

Question 23

What are the two hypotheses about the evolution of coelom?

Answer 23

Gradual evolution: acoelomates -> pseudocoelomates -> coelomates.
Predicted by morphological data

Coelom arose in ancestral bilaterian and was modified, reduced, lost in other lineages. Predicated by molecular data.

Evolutionary flexibility of the coelom has reduced its usefulness as a synapomorphy for bilaterian animals

Question 24

What two major subgroups were found by early studies of embryonic development?

Answer 24

Protostomes and deuterostomes.
First-mouth, second-mouth

Question 25

What is gastrulation and how does it work?

Answer 25

In gastrulation, cells move from outside into the center of the embryo creating the 3 germ layeres.

This creates a pore on the outside called the blastopore.
Blastopore becomes anus and mouth forms later in deuterostomes
Blastopore can become either in protostomes

Question 26

How is the mesoderm formed during gastrulation in protostomes and deuterostomes?

Answer 26

Both Mesoderm-forming process occurs in both groups

Question 27

What is segmentation of body plan?

Answer 27

Segmentation is the division of body or part of body into series of similar structures.

Segmentation enables specialization

Question 28

What is a defining characteristic of vertebrates? Where is it found on the phylogeny?

Answer 28

Segmented backbone.

Monophyletic lineage within chordata. A chordate.

Question 29

Are invertebrates monophyletic or paraphyletic?

Answer 29

Invertebrates are paraphyletic. Segmentation is conspicuous in annelids and arthropods.

Convergent evolution of morphological segmentation occurred in distantly related phyla.

Question 30

What four different ecological roles do animals have in terms of feeding?

Biologists distinguish what they eat from how they eat

Answer 30

Carnivores: feed on animals
Herbivores: Feed on plants and algae
Detritivores: Feed on dead organic matter
Omnivores: Combination of plants, animals, fungi, protists, etc.

Question 31

What is a parasite? What is an endoparasite vs an ectoparasite?

Answer 31

Parasites harvest nutrients from parts of their hosts and are usually much smaller.

Endoparasites live inside their hosts and usually have wormlike bodies.

Ectoparasites live outside their hosts and usually grasp to the host using limbs or mouthparts.

Question 32

What four methods of eating do animals undergo?

Answer 32

1. Suspension feeding: capture food by filtering out particles floating in environment (usually water)
2. Fluid Feeding: suck or mop up liquids like nectar
3. Deposit Feeding: ingest organic material that has been deposited within a subtrate or on its surface
4. Mass Feeding: take chunks of food into their mouths

Question 33

What are the key aspects of cephalization? What are the common senses animals have?

Answer 33

• there is a concentration of sensory organs in the head region
• diversity of sensory abilites and structures among animals
• sight, hearing, taste, smell, touch