Lecture 6 - Cnidarians Flashcards
(32 cards)
how many body layers do they have?
2, epidermis and gastrodermis (mesoglea - connective tissue between the two)
do they have organs?
limited organ development - simple organisms
what 2 forms do they exist in?
1) polyp - sessile
2) medusa - free swimming
how many openings do they have?
1 - feed and expel waste through the same hole
what is a distinctive feature of the group?
presence of nermatocysts (stinging cells)
how do nermatocysts work? ( 5 steps)
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
how often can nermatocysts be used?
only once but get reformed by interstitial cells
what are interstitial cells?
cells which can form into anything
25% of nermatocysts are lost during what process
feeding
which animal reuses nermatocysts
glaucus sea slug eats cnidarians and retains the nermatocysts for protection
what do most cnidarians eat?
most are carnivorous
4 groups of cnidarian and what are they
hydrozoa - hydrozoans
schypozoa - jelly fish
cubozoa - box jelly fish
anthozoa - sea anemones and corals
what is primary polymorphism?
when they have a medusa and polyp stage
secondary polymorphism
different parts of a polyp take on different functions e.g. feeding, reproducing
what do hydrozoans usually live in?
colonies
describe a hydra
freshwater form, not colonial, no medusa or larval stage, female retains egg which then forms polyp
describe siphonophores
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
which stage is dominant in scyphozoans
medusa - v small polyp stage
how do scyphozoans move
pulse umbrella but rely on currents - not strong swimmers
what gives jelly fish their name
thick mesoglea layer
what shape are jelly fish gonads
hore shoe
describe 2 of the jelly fishes senses
1 - simple eyes detect light and dark
2 - statocyst detects gravity
describe jellyfish sexes
have different sexes - produce either egg or sperm
what is a big threat to jelly fish and the effect of it
global temp changes - causing them to move to new areas and cause population explosions in high nutrient areas with knock on effects
