Biodiversity 2: Parazoa and Radiata

Question 1

What does ‘animals are monophyletic’ mean?

Answer 1

It means they have a single common ancestor

Question 2

What was the first key branch point in animal evolution?

Answer 2

Gastrulation results in at least 2 tissue layers (endoderm.ectoderm) vs no gastrulation
→ Separates Parazoa (sponges) from everything else

Question 3

Why are parazoa very unspecialsed?

Answer 3

Because they are neither radially or bilaterally symmetrical

Question 4

What was the second key branch point in animal evolution?

Answer 4

Radial vs bilateral symmetry
→ separates Radiata (e.g jellyfish) from Bilateria

Question 5

Describe Radiata

Answer 5

• Have oral/aboral side
• Dipoblastic (2 tissue layers)

Question 6

Describe Bilateria

Answer 6

• have anterior/posterior and dorsal/ventral sides
• triploblastic (3 tissue layers)

Question 7

What was the third key branch point in animal evolution?

Answer 7

Patterns of cleavage, coelom formation and mouth/anus formation
→ separates protosomes and deutrostomes

Question 8

Give some examples of Protostomes

Answer 8

mollusks, annelids, arthropods

Question 9

What are protostomes patterns of cleavage?

Answer 9

Spiral and determinate

Question 10

When is cell fate determined in protostomes?

Answer 10

Cell fate determined early in development

Question 11

Which phylums are deuterostomes?

Answer 11

Chordata, echinoderms

Question 12

What are deuterostomes patterns of cleavage?

Answer 12

Radial and interdeterminate

Question 13

When is cell fate determined in deutrostomes?

Answer 13

Cell fate is not determined early = early cells can develop into any cell type

Question 14

Describe deutrostomes coelom formation

Answer 14

Folds of archenteron form coelom

Question 15

What is the function of the coelom?

Answer 15

protects organs, allows organ growth

Question 16

Describe protostomes coelom formation

Answer 16

Solid mass of mesoderm splits to form coelom

Question 17

Describe the fate of the blastopore in protostomes

Answer 17

Mouth forms first from the blastopore, anus 2nd

Question 18

Describe the fate of the blastopore in deutrostomes

Answer 18

Anus forms first from the blastopore, mouth 2nd

Question 19

What was the fourth key branch point in animal evolution?

Answer 19

Division of protostomes
→ Separates Lophotrochozoa and Ecdysozoa

Question 20

Describe Lophotrochozoa larvae

Answer 20

Have a crown of cilia (lophophore) on their trochophore larva

Question 21

What are the differences that separate the Lophotrochozoa and Ecdysozoa?

Answer 21

Lophotrochozoa - have specific type of larvae (with a lophophore)

Ecdysozoa - shed their exoskeletons (ecdysis)

Question 22

Which phylum belongs to the sub-kingdom Parazoa?

Answer 22

Porifera (sponges)

Question 23

Describe the Parazoa

Answer 23

Asymmetrical → lack a body axis
No gastrulation
= No true tissues

Question 24

Describe the porifera (sponges)

Answer 24

Simple body plan
Lack muscles, nervous system, organs
Sessile → don’t move and feed passively
Some specialised cells

Question 25

Describe how the Porifera feed.

Answer 25

1. Water drawn into central space (spongocoel) through pores (porocytes) in the sponge wall
2. Drawn in through the action of flagella
3. Water passes out through top of sponge (osculum)
4. Choanocyte (specialised feeding cells) line spongocoel
5. Amebocytes distribute food to rest of the sponges cells

Question 26

Porifera contain amebocytes. What is their other role, aside from food distribution?

Answer 26

Amebocytes also secrete calcium or silica spicules = form sponge framework, gives rigidity

Question 27

Describe the radiata

Answer 27

Radial symmetry
Diploblastic (2 tissue layers)

Question 28

Which phylum belongs to the sub-kingdom Radiata?

Answer 28

Cnidaria (hydras, jellyfish, sea anemones, corals)

Question 29

Describe Cnidaria

Answer 29

Simple form → most ingest food into a blind sac with a gastrovascular cavity

Mouth = anus

Polyp (mouth up) or medusa (mouth down)

No brain, but simple nerve network → can detect stimuli

Contractile bundles of microtubules act like muscles

Question 30

What are the two forms in Cnidaria?

Answer 30

Polyp (mouth up) or medusa (mouth down)
- Sometimes a species will have both forms at different life stages

Question 31

What is the gastrodermis in Cnidaria?

Answer 31

Gastrodermis = absorbs food

Question 32

What is the mesoglea in Cnidaria?

Answer 32

Mesoglea = jelly

Question 33

In Cnidaria, what are the tentacles covered in?

Answer 33

cnidocytes

Question 34

What is the function of cnidocytes?

Answer 34

Used for defence and prey capture
Nematocyst triggered = wraps around prey and injects venom
- Diverse, some have spines/no spines, some have
long threads that stick to prey or entangle small animals

Question 35

What are the 4 groups of Cnidaria?

Answer 35

Anthozoans, Scyphozoans, Cubozoans, Hydrozoans

Question 36

Describe the anthozoans

Answer 36

Anemones & corals
- Polyp stage only
- On the whole, sessile

Question 37

Describe the scyphozoans

Answer 37

True jellyfish
- Medusa form dominates (might be a polyp when young)
- Free swimming

Question 38

Describe cubozoans

Answer 38

Box jellyfish
- Larval polyp stage v different to ‘true jellies’
- Umbrellas cuboid = more streamlined, can move rapidly (7 km/hr)
- Nervous system more developed, complex eyes on rims of bells
- Can see points of light = active predators
- Many are poisonous (Indo-Pacific Sea wasp is most poisonous)

Question 39

Describe the hydrozoans

Answer 39

Hydra, Portuguese Man o’ War, Immortal jellyfish
- Most are colonies of animals
- Some have only medusae / polyps