Lecture 6 - Cnidarians

Question 1

how many body layers do they have?

Answer 1

2, epidermis and gastrodermis (mesoglea - connective tissue between the two)

Question 2

do they have organs?

Answer 2

limited organ development - simple organisms

Question 3

what 2 forms do they exist in?

Answer 3

1) polyp - sessile

2) medusa - free swimming

Question 4

how many openings do they have?

Answer 4

1 - feed and expel waste through the same hole

Question 5

what is a distinctive feature of the group?

Answer 5

presence of nermatocysts (stinging cells)

Question 6

how do nermatocysts work? ( 5 steps)

Answer 6

1 - mechanical/chemical stimulation 
2 - build up of calcium 
3 - changes osmotic pressure
4 - water moves into cell 
5 - out shoots tube injecting protein toxin into prey

Question 7

how often can nermatocysts be used?

Answer 7

only once but get reformed by interstitial cells

Question 8

what are interstitial cells?

Answer 8

cells which can form into anything

Question 9

25% of nermatocysts are lost during what process

Answer 9

feeding

Question 10

which animal reuses nermatocysts

Answer 10

glaucus sea slug eats cnidarians and retains the nermatocysts for protection

Question 11

what do most cnidarians eat?

Answer 11

most are carnivorous

Question 12

4 groups of cnidarian and what are they

Answer 12

hydrozoa - hydrozoans
schypozoa - jelly fish
cubozoa - box jelly fish
anthozoa - sea anemones and corals

Question 13

what is primary polymorphism?

Answer 13

when they have a medusa and polyp stage

Question 14

secondary polymorphism

Answer 14

different parts of a polyp take on different functions e.g. feeding, reproducing

Question 15

what do hydrozoans usually live in?

Answer 15

colonies

Question 16

describe a hydra

Answer 16

freshwater form, not colonial, no medusa or larval stage, female retains egg which then forms polyp

Question 17

describe siphonophores

Answer 17

most sophisticated hydrozoans - whole colony live below a float (not active swimmers rely on wind) - all polyps interact/have a role but survive as 1 organism
- one of the pinnacles of social evolution

Question 18

which stage is dominant in scyphozoans

Answer 18

medusa - v small polyp stage

Question 19

how do scyphozoans move

Answer 19

pulse umbrella but rely on currents - not strong swimmers

Question 20

what gives jelly fish their name

Answer 20

thick mesoglea layer

Question 21

what shape are jelly fish gonads

Answer 21

hore shoe

Question 22

describe 2 of the jelly fishes senses

Answer 22

1 - simple eyes detect light and dark

2 - statocyst detects gravity

Question 23

describe jellyfish sexes

Answer 23

have different sexes - produce either egg or sperm

Question 24

what is a big threat to jelly fish and the effect of it

Answer 24

global temp changes - causing them to move to new areas and cause population explosions in high nutrient areas with knock on effects

Question 25

3 features of cubozoa (box jelly fish)

Answer 25

1 - small and v toxic
2 - active swimmers - pursue prey
3 - sophisticated eyes - 24 eyes

Question 26

describe how anthozoans live

Answer 26

only found in polyp stage

- colonial or solitary

Question 27

2 features of anthozoan structure

Answer 27

water circulates through holes to aid respiration

use water for hydrostatic skeleton

Question 28

anthozoan reproduction

Answer 28

1 - asexual (pedal laceration or longitudinal fission)

2 - sexual (hermaphrodite)

Question 29

example of an anemone symbiotic relationship

Answer 29

clown fish and sea anemone both benefit
anemone provides protection
fish keeps it clean
clown fish colour warn of anemone toxicity

Question 30

example of a coral symbiotic relationship

Answer 30

coral and algae
algae convert co2 into carbohydrate for coral
polyp produce nitrogenous waste for algae to use

Question 31

what is coral bleeching

Answer 31

coral lose algae by process of climate change

Question 32

what is the most basal group of cnidaria

Answer 32

anthozoa

hydrozoa and scyphozoa are more derived - developed medusa stage