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2nd Year: Animal Biodiversity > Cnidarians > Flashcards

Flashcards in Cnidarians Deck (41):
1

Give 3 synapomorphies of cnidarians.

1. Radial symmetry
2. A gastrovascular cavity with a single opening surrounded by tentacles
3. Nematocysts

2

Define a nematocyst.

A stinging cell with a barbed and venomous coiled thread that shoots out. These occur in raised batteries along the tentacles.

3

Is the nervous system central or decentralised?

Decentralised, have nervous 'nets' throughout the body.

4

Cnidarians are coelenterates. Define a coelenterate.

An organism with a hollow body cavity (as opposed to coelomates which are fluid/organ filled).

5

Do cnidarians possess mesoderm?

No: the have mesoglea, a jelly layer, rather than true mesoderm. They do have ectoderm and endoderm.

6

Coelenterates are the simplest organisms at tissue grade. True or false?

True.

7

What are the 2 body forms of cnidarian?

1. Medusae
2. Polyps

8

Define a medusa.

The oral surface faces downwards. These species have thick mesoglea and are pelagic. They can grow very large and tend to have complex polymorphic lifecycles.

9

Define a polyp.

The oral surface faces upwards. These species have thin mesoglea. Polyps are sedentary.

10

Polyps display modular growth. Define modular growth.

Asexual reproduction whereby the zygote develops into a discrete organism and, instead of growing into a whole organism, produces more units like itself.

11

Give the 4 main classes of cnidarian.

1. Scyphozoa: the jellyfish
2. Hydrozoa: the hydras
3. Cubozoa: the box jellies
4. Anthozoa: the anemones and corals

12

What do the anthozoans possess that the other classes do not?

Septa: radial partitioning of the gastrovascular cavity.

13

Corals are not individual organisms but colonies of what?

Polyps.

14

How are anemones and corals distinguishable?

Coral polyps have a calcitic skeleton. Anemones do not.

15

The septa (that partition the gastrovascular cavity) are calcified and form the what?

Corallite: a cup-like skeleton

16

There are 2 types of coral, depending on lifestyle. What are they?

1. Hermatypic: reef-bulding corals

2. Ahermatypic: non-reef-building corals

17

What conditions do hermatypic corals prefer?

Sheltered, shallow, warmer waters with high light intensity.

18

What conditions do ahermatypic corals prefer?

Areas with more wave action that are deeper, colder and darker.

19

Why are hermatypic corals restricted to warm areas with lots of sunlight?

They often enter symbioses with zooxanthellae (algae), and the algae need to photosynthesise.

20

What are corals that enter symbioses with zooxanthellae referred to as?

Z-corals

21

Corals display modular growth. This can be achieved via 2 methods, which are?

1. Budding: a smaller, identical polyp splits from the adult

2. Division: An adult unit splits in two

22

Define a zooid.

The polyp that results from modular growth.

23

There are 2 fates for coral zooids. What are they?

1. Clonoteny: zooids grow incompletely and are retained by the parent colony.

2.

24

There are 2 fates for coral zooids. What are they?

1. Clonoteny: zooids grow incompletely and are retained by the parent colony. Zooids differentiate into different structures as part of the whole.

2. Clonpary: zooids grow to completion and split off to begin a separate existence.

25

Define a ramet.

A shed zooid in clonopary.

26

Give 4 advantages of modular growth.

1. Rapid reproduction rate
2. Increase in biomass but no decrease in SA:V ratio]3. Easy to replace dead units/spread colony
4. Delayed senescence

27

Why do the same species of coral grow into such different colonial morphs?

They are shaped by wave action and modular growth allows great plasticity.

28

Corals can also reproduce sexually. True or false?

True.

29

The majority of coral reproduction is actually sexual. Why?

Most corals are gonochoristic (single sex), thus increases genetic diversity.

30

There are 2 classes of sexually reproducing coral. What are they?

1. Broadcasters: colonies release their gametes into the water for external fertilisation.

2. Brooders: only sperm cells are released which land on waiting egg carries below for internal fertilisation.

31

Broadcasting species are hermaptypic. True or false?

True.

32

Why do hermatypic broadcasting corals have synchronous spawning events?

It ensures gamete fusion will occur.

33

Define planulae.

Microscopic coral larvae.

34

In broadcasting species planulae exhibit sono/phototaxis. Why?

So they can find densely populated, light areas to settle in.

35

What happens to the planulae of brooding corals?

They are released and ready to settle.

36

Corals are carnivorous. How do they hunt?

They use their tentacles and mesenteral filaments to hunt zooplankton.

37

There are specialised detritivore corals with sweeper tentacles. True or false?

True.

38

Why are corals commonly mistaken for autotrophs?

Because of the photosynthetic algae in Z-corals.

39

Z-corals are all facultative symbionts. True or false?

False: most are obligate symbionts.

40

In Z-corals, growth forms seek to maximise surface area. Why?

So the zooxanthellae can photosynthesise better.

41

AZ-corals (those without symbionts) do not usually form colonies. True or false?

True: they can do, but do not usually.