Cnidarians Flashcards
Cnidarian body structure
Only have 2 body layers - epidermis (outer) and gastrodermis (inner)
Connective tissue in between - mesoglea
-can be thick or thin - depends on animal
-lost their anus potentially as sister group has it still, adaptive for how they live to have lost it
Polyp and medusa structure
Polyp... -sessile -gut in gastrovascular cavity -tentacles on top surrounding single opening Medusa... -same as polyp but upside-down
Cell types in cnidarians
Epitheliomuscular cells - muscle system of animals
-have muscle fibres running along bottom of cell
Receptor cells - detect stimuli, often found on tentacles
Interstitial cells - capable of transforming into other cells
Cnidocil/nematocysts - distinctive to the group, stinging cells for prey capture
Stinging process
- Upon stimulation (chemical or mechanical) build up of calcium
- Changes osmotic pressure and water enters cell
- Lid opens and dart-like structure with barbs on shoots out and penetrates prey
- Can inject protein toxin too
- Cannot reuse but will be reformed by interstitial cells
- 25% are lost in feeding to get prey
- seaslugs are found to have them by eating cnidarians
Hydrozoan colonial forms
Show secondary polymorphisms - take on different functions
Gastrozooid is responsible for feeding in the colony
Gonozooid is responsible for reproduction
Dactylozooids are defensive polyps
Obelia and Hydra
Obelia is colonial - its gonozooid's bud off and take the medusa form -either male or female -come together for fertilisation -egg forms larval stage -lifecycle repeats into colonial polyp form Hydra is not colonial (unlike most) -freshwater form -no medusa or larval stage either
The most sophisticated hydrozoans…
Siphonophores
Have colonies of individuals with different things that are hanging off below a swimming bell
Quite extensive colonies - parts for reproduction, digestion, defence etc.
Wilson considered 1/4 pinnacles of social evolution
Portuguese man of war - very sophisticated
Rely on wind and weather for movement
Scyphozoa body plan
Medusa phase dominant (do have polyp but insignificant)
Muscle layer on surface which creates contractile force allowing them to move their umbrella - not great swimmers
Gastrovascular cavity with 4 pouches containing gonads
Scyphozoa lifecycle
- Sperm and egg form planula larva
- Forms polyp
- Grows and starts dividing by traverse fission
- The young media pops out from the top
Scyphozoa sensory features
Pigment cup eyes - detect light and dark
Statocyst which detects gravity
Rhopalium which is a few nerve cells that controls the rhythms of contractions
Cubozoa
Similar lifecycle to true jellyfish Toxic and venomous Active swimmers - at around 2m/sec Active predators Feed on fish etc. 24 of which some are simple and some are like octopi or vertebrate, with a lens, cornea and retina
Anthozoa features, body plan and digestion
Only found in the polyp stage - no medusa at all
Colonial or solitary
Have septa running through animal to increase SA
-allows water to circulate through the animal, good for respiration, waste removal and diffusion
-acts as kind of hydrostatic skeleton
Phagocytic cells take up mush from food - intracellular digestion (like other cnidarians)
Anthozoan asexual reproduction
Pedal laceration - slide along the substrate and drop off parts of themselves which regrow a new individual
Longitudinal fission - constrict down middle and forms two new individuals
Anthozoan sexual reproduction
Hermaphrodites
Produce eggs and sperm at different times to avoid self-fertilisation
Fertilisation takes place either in GVcavity or externally
Planula larva attach to substrate and develop on
Anthozoan symbiotic relationship with clown fish
Clown fish doesn’t get stung by the anemone so provides protection for fish
Fish gets more oxygen in there by wafting and moving - also cleans anemone
Anemone gets fishes left over food and vice versa
Clown warning colouration to advertise toxicity of anemone
