Lecture 5

Question 1

What are cnidarians?

Answer 1

• Radially symmetrical
• Oral-aboral axis
• Polyp or medusae body plans
• Ectoderm and gastroderm
• Separated by mesoglea
• No central brain or heart
• Incomplete gut
• Nerve net and muscles are present
• Special cnidocysts

Question 2

Cnidocysts

Answer 2

‘Stinging cells’; specialized neural cells that typify the phylum cnidaria

Question 3

Anthozoans (examples)

Answer 3

• Sea plants, anemones, gorgonians, organ-pipe corals, stony corals
• About 7200 species; largest cnidaria class

Question 4

Body plans (anthozoan)

Answer 4

• Always polyp body plans
• No body plans outside and inside the body
• Primary component of global coral reef communities

Question 5

Hydrozoa (examples)

Answer 5

• Hydroids, fire corals, hydromedusae
• About 3000 species

Question 6

Scyphozoa (examples)

Answer 6

• True jellyfish
• About 200 species

Question 7

Body plans (Hydrozoa)

Answer 7

• Alliterating of generations of polyp and medusas stages

Question 8

Body plans (Scyphozoa)

Answer 8

• Polyp stage often absent or reduced
  
  • When polyp, they undergo asexual strobilation

Question 9

Strobilation

Answer 9

(Transverse fission) a form of asexual reproduction consisting of the spontaneous transverse segmentation of the body

Question 10

Cubozoa (examples)

Answer 10

• Box jellyfish and sea wasps
• About 51 species

Question 11

Body plans (cubozoa)

Answer 11

• Primarily medusae forms
• Lack strobilation
• Cube shaped bell
• Possess eyes and advanced neural rings
• Potent venoms

Question 12

Staurozoa (examples)

Answer 12

• Stalked jellyfish
• About 50 species

Question 13

Body plans (staurozoa)

Answer 13

• No medusae stage exists

Question 14

Myxosporea (examples)

Answer 14

• Obligate parasites
• About 2300 species

Question 15

Body plans (myxosporea)

Answer 15

• Very small and unicellular
• Evolution has led to the loss of many genes needed for development, metabolism, and cell-cell communication

Question 16

Polyp body plans

Answer 16

• Cylindrical
• Mouth surrounded by tentacles
• Sessile or sedentary lifestyle
• Radial symmetry

Question 17

Medusae body plans

Answer 17

• Bell shaped with tentacles hanging downward
• Free swimming
• Pelagic lifestyle adaptations
• Mesoglea is usually quite thick
• Alternation between body plans

Question 18

Metagenesis

Answer 18

The transition between sexual and asexual phases of an organism in its lifecycle

Question 19

Asexual reproduction

Answer 19

• Budding; common in polyps
• Fragmentation; corals and anemones often use this

Question 20

Fragmentation

Answer 20

• Asexual reproduction
• A type of cloning where one organism is divided into minor fragments. Once divided these fragments develop into individual ones

Question 21

Sexual reproduction

Answer 21

• External fertilisation
• Broadcast spawning

Question 22

Broadcast spawning

Answer 22

• The release of gametes into open water for external fertilisation
• Fertilised eggs develop into free swimming planula larvae
• Planula settle to form polyps

Question 23

Lifecycle of jellyfish (moon jelly)

Answer 23

1.) Medusa produces gametes and releases
2.) Leads to polyp stages
3.) Polyps sexually reproduce to form medusae

(Large degree of variance as some classes done even use polyp phase)

Question 24

Cnidarian tree of life

Answer 24

Are amongst the most ancient form of like, being a sister (likely paraphyletic) to placozoa

Question 25

Paraphyletic

Answer 25

Descended from a common evolutionary ancestral group, but not including all the descendant groups