Cnidaria

Question 1

Summary

Answer 1

Introduction
Key characteristics
Body structure
Cnidae
Feeding
Life cycles and reproduction
Sexual and asexual
Classes
Hydrozoa, Scyphozoa, Cubozoa, Alcyonaria, Zoantharia

Question 2

introduction

5 points

Answer 2

1. “Coelenterates”; old term, still used
2. Very diverse group
3. Can be sessile, sedentary or pelagic
4. Occur at all depths
5. entirely aquatic and mostly marine

Question 3

Classification

Kingdom, phylum, subclass, class

Answer 3

Kingdom: Metazoa

Phylum: Cnidaria

Sub phylum: Medusozoa
Class: Hydrozoa, Scyphozoa, Cubozoa

Subphylum: Anthozoa
Class: Alcyonaria, Zoantharia

Question 4

Key characteristics (not shared across all species)
6 points

Answer 4

1. Radially symmetrical
2. Diploblastic
3. Possess cnidae (sting)
4. Single body cavity
5. No nervous system - Nerve net
6. Alternation of generations
   Asexual polypoid and sexual medusoid stages
7. Cilliate planula larvae

Question 5

Body structure

3 points

Answer 5

Diploblastic
1. Outer ectoderm 
2. Inner entoderm 
3. Separated by noncellular 
mesenchyme

Question 6

Nematocysts/Cnidae (sting)

4 points

Answer 6

1. Unique to cnidarians
2. Three types
   Penetrant
   Glutinant
   Volvent
3. Produced in both cell layers from cnidoblasts, becoming cnidocytes
4. Single-use

Question 7

Feeding

5 points

Answer 7

1. Mostly ambush predators,
2. some suspension feeders
3. Use nematocyst covered feeding tentacles to capture prey
4. Prey partially digested in gastrovascular cavity (coelenteron), completed in food vacuoles
5. Pseudofeaces everted

Question 8

Life cycle- alternate generations
polypoid
5 points

Answer 8

1. Occur in all classes
2. Sessile/Sedentary, tubular
3. Can reproduce asexually
4. Some form colonies
5. Radially symmetrical
   Biradial and quadriradial

Question 9

Life cycle
Medusoid
5 points

Answer 9

1. Occur in all classes of Medusozoa, not anthozoa
2. Free swimming, bell or disc-shaped structures
3. Pulsating propulsion
4. Radially symmetrical
5. Reproduce sexually, usually dioecious
   planktonic larvae

Question 10

Reproduction - sexual

3 points

Answer 10

1. Medusa stage produces gametes
2. Planula larvae
3. Develop into benthic polyp stage

Question 11

Reproduction - asexual

5 points

Answer 11

1. Polyp stage
2. Forms colonies
   Modular polymorphism
3. Budding
4. Fragmentation
5. Fission

Question 12

Symbiosis

Answer 12

1. Common among cnidarians

Question 13

Medusozoa 
class hydrozoa 
3 points

Answer 13

1. Simplest cnidarians with alternating generations
2. Benthic colonial stage may be polymorphic (lots of different forms)
3. Small medusa may remain attached to polyp stage

Question 14

Medusozoa
Class Scyphozoa
2 points

Answer 14

1. True jellyfish

2. Dominant, well-developed medusa phase.

Question 15

Medusozoa

Class Cubozoa

Answer 15

1. Cubomedusae, box jellyfish
2. Polyps produce a single medusa
3. Square-shaped medusa
4. Well-developed eyes
5. Toxic nematocysts (cell in tentacles)

Question 16

Bioluminescence

3 points

Answer 16

1. Common in hydrozoa and scyphozoa
2. Produce luciferin de novo, reacts with oxygen to produce light
3. e.g. attracts prey

Question 17

Anthozoa
Class Alcyonaria
5 points

Answer 17

1. Sea pens, sea fans and soft corals
2. Modularly colonial
   Non-polymorphic
3. No medusa stage
4. Internal support system
5. Pinnate tentacles, arranged in eights

Question 18

Anthozoa
Class Zoantharia
6 points

Answer 18

1. Sea anemones, hard corals
2. Solitary or modularly colonial
3. Non-polymorphic
4. No medusa stage
5. Various levels of external support
6. Polyps have simple tentacles in multiples of six