1: Cnidarians

Question 1

What are the 4 groups of Cnidarians?

Answer 1

Hydrozoa (hydrozoans)
Scyphozoa (jellyfish)
Cubozoa (box jellyfish)
Anthozoa (sea anemones, corals)

Question 2

Describe the structure of the radiata

Answer 2

• 2 body layers:
  (Epidermis, Gastrodermis, Mesoglea between them)
• One opening - mouth/anus
• Limited organ development

Question 3

Describe the cell types present in the radiata and their function

Answer 3

Epitheliomuscular cells → contractile muscle-like layer
Interstitial cell → totipotent
Receptor cells → detect ques from environ
Cnidocytes → stinging cells (nematocysts most common type)

Question 4

Describe the nematocysts

Answer 4

→ stinging cells
Can only be used once → 25% lost in feeding
Reformed by interstitial cells (totipotent)

Question 5

How do nematocysts work?

Answer 5

When stimulated, release of Calcium in the cell = changes osmotic pot so water drawn in.

Question 6

What are the 2 forms of the Cnidarians

Answer 6

Polyp & medusa

Question 7

What morph do the Cubozoans have?

Answer 7

Both Polyp and Medusa (but medusa is dominant)

Question 8

What morph do the hydrozoans have?

Answer 8

Usually both polyp and medusa

Question 9

What morph do anthozoans have?

Answer 9

Only Polyp

Question 10

Describe reproduction in the Cnidarians

Answer 10

• Alternation of generations
• Polyp produces medusa → sexual stage
• Some only have polyp OR medusa stage
• Freshwater → no medusa or larvae stage → direct development due to harsh environ (osmotic regulation)

Question 11

Describe reproduction in the Scyphozoans

Answer 11

Scyphozoan: female/male = eggs/sperm → larvae → polyp stage → medusa

Question 12

Describe repro in the Cubozoans

Answer 12

Cubozoans: female/male = eggs/sperm → larval stage → polyp stage→ transforms directly into medusa.
- Mating behaviour & internal fertilisation has been observed

Question 13

Describe repro in the Anthozoans

Answer 13

Anthozoans: no medusa stage
Fertilised egg → Planula → Polyp → Young anenome polyp → adult

Question 14

Describe the sense organs in the Scyphozoa

Answer 14

(jellyfish)
Rhopalium → responsible for controlling pulse rate of umbrella
Connected to nerve net
Ocellus → simple pigment eyes
Statocyst → detecting gravity

Question 15

Describe the sense organs in the Cubozoans

Answer 15

(Box jellies)
- 24 eyes in rhopalia
Upper & lower lens eyes
Pit eyes (detect light)
Slit eyes (detect movement)
- 4 rhopalia, 6 eyes in each (upwards and downwards facing eyes)
- Active swimmers, chase prey (unlike jellyfish)

Question 16

Describe the Siphonophores

Answer 16

E.g Portuguese Man o’ war/ Pacific Man o’ War
- Polyp and medusa individuals
- Complex colonies of polypoid & medusoid individuals
- 1000 zooids
- One of the pinnacles of social evolution (E.O Wilson)
- Understudied!