Phylum Cnideria Flashcards
Where are cnidarians found, and how many of them are there?
- tropics & poles
- mostly saltwater (though some in fresh)
- found at surface and depths (some burrow)
- about 9000 species
What is the relevance of the name Cnidaria?
“Cnidos” means stinging nettle in Greek
Features of Cnidaria
- soft bodies
- carnivores
- stinging tentacles around mouths
- 2 cell layers (ectoderm & endoderm with mysoglea in btwn)
- simplest animals with symmetry and true tissues
- no bones, complex brains, eyes, or hearts
Defence & Hunting
- Cnidocytes: stinging cells along tentacles. Contain nematocysts.
- nematocysts: poison-filled stinging harpoons.
- when something touches the cnidarian, trigger on cnidocyte is pushed and nematocyst is plunged into prey
- position is released that can paralyze or kill prey
Body
- radial symmetry
- can be polyp, medusa, or both
- diploblastic
Polyp
- cylindrical body with arm-like tentacles
- mouth points upwards
- usually sessile
Medusa
- bell-shaped body with tentacles hanging down
- mouth points down
- motile
Movement in Medusas
Jet propulsion
Movement in polyps
Hydrostatic skeleton: layer of circular muscles & longitudinal muscles allowing them to bend, flex, or close their tentacles or opening
Respiration
- through diffusion in cells (no specialized circulation - nutrients, oxygen, & waste are all transferred through diffusion)
- higher concentrations of oxygen move into cells with lower concentrations
Feeding
- Cnidarian captures prey & pulls it into its mouth with tentacles
- digestion occurs in gastrovascular cavity using digestive enzymes. Gastroderm cells absorb the nutrients
Budding
- asexual reproduction
- polyps
- 2 types:
- swelling on side of Cnidaria grows into new polyp
- polyp produces tiny medusas that separate and become individuals
Excretion
- waste & CO2 are diffused out
- waste accumulates in gastrovascular cavity and are expelled through the mouth
Sensory cells
- nerve net: group of sensory cells to help organism respond to environment. Distributed evenly around organism, but some have a higher concentration at the mouth
- stratocysts determine direction of gravity
- ocelli: eyespots that detect light
Class Schphozoa
- true jellyfish
- thick mysoglea
- starts as polyp which buds into medusa, then stays a medusa for rest of life
- can be tiny or huge
Class Hydrozoa
- usually in polyp form (if medusa form is found, it’s very small)
- found in diverse ecosystems
- look different (ex. From hydra to Portuguese man of war)
- thinner mysoglea
Class Cubozoa
- uncommon
- only found in tropical/subtropical waters
- plantula (larvae) buds off into a single cubozoa
Class Anthozoa
- polyps only
- ex. Sea anemones and corals
- can be solitary or colonial
- divided into:
- stony coral & anemones
- soft corals & sea fans/pens
Why coral reefs are dying:
- global warming
- increased sedimentation
- degraded water quality
- disease
- increased storm activity & damage
- vessel & tourism damage
Strobilation
- asexual
- Several young are stacked on top of each other and split off into multiple medusas
Relationship between algae and coral
- mutualistic
- coral protects algae & helps it w/photosynthesis
- algae provides oxygen, glucose, etc. & help coral remove wastes
Stauromedusae
- spend life attached to rocks instead of swimming freely
- usually found in cold water
- have been found in hydrothermal vents
Corals & coral bleaching
- made up of calcium carbonate skeletons from polyps
- bleaching occurs when polyps expel algae cells due to stress, leaving the coral white
