Phylum Cnidaria

Question 1

who are they

Answer 1

-	~1000 species found in water 
o	Mostly marine 
o	5 main classes → only talk about 4
-	2 main forms (polyp and medulla)
-	Unique stinging cells (cnidocytes)
-	Gelatinous layer called mesoglea
-	Blind ended gut with tentacles around mouth 
o	No anus, mouth that goes into a sac and then stuff is digested and goes out the way it came
-	Both asexual and sexual reproduction

Question 2

levels of organization

Answer 2

• Tissue grade
  o Groups of cells that carry out a specific function
  o Tissues formed from early stages of embryo

Question 3

diploblastic

Answer 3

• 2 true tissue layers
• Zygote → blastula (hollow ball) → invaginates in gastrulation, folding inward → what causes 2 layers
• Inside of gastrula becomes endoderm and then ectoderm on outside
• Opening of gastrula = blastopore that becomes mouth
• Doesn’t invert all the way so becomes blind ended gut

Question 4

symmetry

Answer 4

• Radial → no dorsal or ventral side
• Where the mouth is (oral end) and aboral side (where bottom attaches)
• Can sense environment on all sides → no head
  o Very good for sessile and free floating animals because they are sort of helpless

Question 5

diploblast but has 3 layers

Answer 5

• Only 2 tissues
• Endoderm = gastrodermis, stomach lining
• Ectoderm = epidermis, skin outer coating
• Mesoglea = jelly (not cellular) (not living)
• In the middle is the gastrovascular cavity → extracellular digestion, secretes digestive enzymes and absorbs nutrients

Question 6

2 body forms

Answer 6

• Dimorphic
• Polyp:
  o Anemone
  o Sessile most of the time → not always
  o Solitary or colonial forms (like coral)
• Medusa
  o Swimming
  o Jellyfish
• In polyp crazy stuff can happen → polymorphism
• Also called zooids → used for feeding (gastrozooids) reproduction (gonozooids) defense (dactylzooids)

Question 7

reproduction

Answer 7

• Alternation of generations → polyp, medusa, polyp, medusa
• Polyp = asexual to make medusa
• Medusa goes through meiosis to make polyp
• Gametes fuse to a planula larva
• Planula settles to make new polyp
• One group is an exception

Question 8

cnidocyte –> nettle cell

Answer 8

• Cnidocyte = cell (invagination of epithelium)
• Cnidae = capsule within cell → contains nematocyst organelle and stings
• Most notable cnidae is the nematocyst → hair like triggercauses sea water to rush in and inject nematocyst
• Once discharged skin reabsorbs it and makes a new cell
• Rapid → hydrostatic pressure increase
• One time only

Question 9

class anthozoa

Answer 9

• Over half of all cnidarians (6000+ species)
• Flower animals → polyps only
• Sexually reproduce in polyp forms (usually medusa that is sexual)
• Anemones, corals
• Well divided, tubular body and pharynx, large gastrovascular cavity

Question 10

subclass hexacorallia

Answer 10

• 6 axes of symmetry
• Anemones
• Stony/true/hard corals
  o Mini sea anemones in calcareous cups
  o hard reef corals (coral reefs dominated by them

Question 11

subclass octocorallia

Answer 11

• 8 part symmetry
• Soft corals, sea pansies, sea pens, sea fans
• Gorgonian corals (deep sea, cold water)
  o Proteinaceous fleshy bodies filled with CaCo spicules
  o Calcareous spicules only in mesoglea endoskeleton
  o Mostly colonials

Question 12

ecological importance of anthozoa

Answer 12

• Habitat creation (coral reefs)
• Harbors photosynthetic dinoflagellates (zooxanthellae)
  o Helps create food for coral → water lwo in food and nutrients clear = low plankton so dinoflagellates provide food
  o Coral bleaching → expels dinoflagellates and coral dies
• Coral reefs
  o Biodiversity hotspots
  o Tropical and deep sea ecosystems
  o Habitats
  o 25% of marine life
• Mutualism with anenomes
  o Fish with special mucus that starts firing nematesis
  o Crabs use for protection because anemones sting so thigns wont eat crab

Question 13

class hydrozoa

Answer 13

• Very morphologically different
• Only class with freshwater → ex. hydra (no medusa, can bud to new hydra)
• Most are colonial and exhibit polymorphism → ex obelia, very typical lifecycle of cnidarians
• Can have a dominant medusa stages

Question 14

siphonophores

Answer 14

• All polyp forms

Question 15

class scyphozoa

Answer 15

→ true jellies
- 200-400 species
- Small or big
o Biggest = 7.6 feet wide
- Dioecious (separate sexes)
- Sting → nematosis not as bad as other types
- Not hermaphrodites
- Around mouth are big, fleshy oral lobes
o Manubriam bigger, filled with nematosis
o Can adapt really quickly
- Strobilation and reproduction
o Follows typical life cycle
o Nneds to settle as polyp long enough to make medusa
o Strobula → tiny ephyra

Question 16

class cubozoa

Answer 16

• Cube jellies
• Specialized structure, tentacles come off as corners
• Rophalia = eyes (no brain though!), used to help move around water
• Very toxic chironex flekeri ca be fatal even thogh its very tiny