Phylum Cnideria

Question 0

Where are cnidarians found, and how many of them are there?

Answer 0

• tropics & poles
• mostly saltwater (though some in fresh)
• found at surface and depths (some burrow)
• about 9000 species

Question 1

What is the relevance of the name Cnidaria?

Answer 1

“Cnidos” means stinging nettle in Greek

Question 2

Features of Cnidaria

Answer 2

• 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

Question 3

Defence & Hunting

Answer 3

• 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

Question 4

Body

Answer 4

• radial symmetry
• can be polyp, medusa, or both
• diploblastic

Question 5

Polyp

Answer 5

• cylindrical body with arm-like tentacles
• mouth points upwards
• usually sessile

Question 6

Medusa

Answer 6

• bell-shaped body with tentacles hanging down
• mouth points down
• motile

Question 7

Movement in Medusas

Answer 7

Jet propulsion

Question 8

Movement in polyps

Answer 8

Hydrostatic skeleton: layer of circular muscles & longitudinal muscles allowing them to bend, flex, or close their tentacles or opening

Question 9

Respiration

Answer 9

• 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

Question 10

Feeding

Answer 10

• Cnidarian captures prey & pulls it into its mouth with tentacles
• digestion occurs in gastrovascular cavity using digestive enzymes. Gastroderm cells absorb the nutrients

Question 11

Budding

Answer 11

• asexual reproduction
• polyps
• 2 types:
  - swelling on side of Cnidaria grows into new polyp
  - polyp produces tiny medusas that separate and become individuals

Question 12

Excretion

Answer 12

• waste & CO2 are diffused out

- waste accumulates in gastrovascular cavity and are expelled through the mouth

Question 13

Sensory cells

Answer 13

• 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

Question 14

Class Schphozoa

Answer 14

• true jellyfish
• thick mysoglea
• starts as polyp which buds into medusa, then stays a medusa for rest of life
• can be tiny or huge

Question 15

Class Hydrozoa

Answer 15

• 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

Question 16

Class Cubozoa

Answer 16

• uncommon
• only found in tropical/subtropical waters
• plantula (larvae) buds off into a single cubozoa

Question 17

Class Anthozoa

Answer 17

• polyps only
• ex. Sea anemones and corals
• can be solitary or colonial
• divided into:
  - stony coral & anemones
  - soft corals & sea fans/pens

Question 18

Why coral reefs are dying:

Answer 18

• global warming
• increased sedimentation
• degraded water quality
• disease
• increased storm activity & damage
• vessel & tourism damage

Question 19

Strobilation

Answer 19

• asexual

- Several young are stacked on top of each other and split off into multiple medusas

Question 20

Relationship between algae and coral

Answer 20

• mutualistic
• coral protects algae & helps it w/photosynthesis
• algae provides oxygen, glucose, etc. & help coral remove wastes

Question 21

Stauromedusae

Answer 21

• spend life attached to rocks instead of swimming freely
• usually found in cold water
• have been found in hydrothermal vents

Question 22

Corals & coral bleaching

Answer 22

• made up of calcium carbonate skeletons from polyps

- bleaching occurs when polyps expel algae cells due to stress, leaving the coral white