Porifera, Cnidaria and Ctenophora Flashcards
Cnidaria
True tissues
Diploblastic: two germ layers
Radial symmetry
Wide range sessile & motile forms
~ 10,000 species, includes corals, anemones & jellies
What does Diploblastic mean?
There are two germ layers- endoderm & ecoderm
In the Cnidaria these are separated by mesoglea- a jelly like matrix
Variation in the body plan: Polyp or Medusa
Cnidaria nervous system
No brain – simple reflex pathways
Nerve cells interact with sensory and contractile cells
Nerve Net coordinates movement
Lifestyle
Predatory lifestyle – carnivorous
Extensible tentacles capture prey, passed to Gastrovascular Cavity
Tentacles armed with Cnidocyte cells – unique
Cnidae
Cnidae (pl) are capsule like organelles – a homologous trait for this group
Nematocysts are specialised Cnidae
Nematocysts produce stinging threads that penetrate body wall of prey/enemies
Other Cnidae are involved in sticking/entangling
Modern Cnidaria divided into four Classes
Corals & anenomes
Hydras / hydroids
“Jellyfish”
Box jellies
Hydrozoa
Normally alternate between polyp & sexual medusa stages
Colonial lifestyle common: multiple individuals combine to make one apparent organism
Hydra are highly regenerative and show little evidence of senescence
Scyphozoa
True jellies, sea nettles
All marine
Most larger jellies, largest 2m diameter, 60-70m tentacles
Medusa predominant stage Shallow coastal to 3000m
Many are bioluminescent
Cubozoa
Box jellies and sea wasps
All marine, tropics
Complex eyes on fringe
Strong swimmers
Active hunters, prey mainly fish
Extremely potent venom
Anthozoa (flower animals)
Sea anemones, most corals, sea fans
Only occur as polyps
Ctenophores
Also known as Comb Jellies, Sea Walnuts
~100 species, all marine
Radial symmetry, diploblastic
8 ciliated longitudinal rows (combs) use for propulsion
Long, branched, contractile tentacles
The tentacles have cells called colloblasts
Colloblasts are sticky and function in entrapment.
All are hermaphrodites
Many are bioluminescent
Only 100 named species
