Inverts - Cnidarians

Question 1

Cnidarian symmetry

Answer 1

Radial

Question 2

Body layers

Answer 2

• Epidermis and gastrodermis
• One opening for mouth and anus
• Limited organ development

Question 3

4 groups of Cnidarians

Answer 3

Hydrozoa (Hydrozoans)

Scyphozoa (Jellyfish)

Cubozoa (Box jellyfish)

Anthonzoa (Sea anemones & Corals)

Question 4

Scyphozoa

Answer 4

Jellyfish

Question 5

Cubozoa

Answer 5

Box jellyfish

Question 6

Anthonzoa

Answer 6

Sea anemones and corals

Question 7

What is the Mesoglea?

Answer 7

Layer between epidermis and gastrodermis

Question 8

Epidermis cell types

Answer 8

Longitudinal and circular muscle fibres

interstitial cells - totipotent

Neuron - simple nerve net

Question 9

Gastrodermis cell types

Answer 9

Enzymatic gland cells - food breakdown

Nutritive muscle cell - takes up food in vacuoles (intracellular)

Question 10

Cnidocytes (nematocytes)

Answer 10

• Mechanical and chemical stimulation
• Used to catch prey
• Formed by interstitial cells

Question 11

Polymorphism: what are the two forms?

Answer 11

• Polyp and medusa
• medusa - sexual stage
• Sessile or free swimming
• Can alternate between two forms - alternation of generations
• Anthozoans only live in polyp stage

Question 12

Process of nematocyst mechanism

Answer 12

Mechanical and chemical stimulation causes the release of calcium within the nematocyst

This changes the osmotic potential and water gets drawn in because it becomes more concentrated

Lid gets flipped open, releasing the coiled tube

Can only be used once

Reformed from interstitial cells (totipotent)

Question 13

Secondary polymorphism

Answer 13

Within the polyp there are other types of specialisations

Different part of the polyp do different things

Question 14

Secondary polymorphism within Hydrozoa (example)

Answer 14

gonozooid (sexual part)

Gastrozooid (feeding part)

Dactylozooid (defence part)

Question 15

Siphonophores (man o’war)

Answer 15

Complex colonies

made up of polyp and medusa individuals

can have up to 1000 zooids

Question 16

Sense organs in jellyfish

Answer 16

1. Rhopalium
2. Ocellus
3. Statocyst

Question 17

Rhopalium function (jellyfish sense organ)

Answer 17

controls pulse rate (beat) of the ‘umbrella’

Question 18

Ocellus function (jellyfish sense organ)

Answer 18

simple pigment type eye

found within rhopalium

detects light

Question 19

Statocyst function (jellyfish sense organ)

Answer 19

Detects gravity

ensures jellyfish is the correct way up

Question 20

Box jellyfish eyes

Answer 20

• Upper and lower lens eye
• similar to vertebrate & cephalopod eyes
• pit eyes detect light
• slit eyes detect movement
• located in the rhopalium
• 24 eyes

Question 21

Box jellyfish - Upper and lower eyes

Answer 21

• Lower eye detects obstacles in the water
• Upper eye detects landmarks
• e.g. mangroves (where they feed)

Question 22

Symbiotic relationships

Answer 22

Clownfish - sea anemone

• fish ‘prune’ dead bits of the anemone & swim about which aerates the anemone - fish gets protection

Stony corals - Zooxanthellae algae

• live in the coral gastrodermis
• corals feed off algae

Question 23

Why are jellyfish blooms problematic?

Answer 23

Effect tourism

jellyfish eat young fish and cause population crashes

sting can be painful

Question 24

freshwater hydra reproduction

Answer 24

Don’t have a polyp or larval stage

Freshwater = harsh environment

Question 25

Box jellyfish (cubozoans) reproduction

Answer 25

Go straight from polyp to medusa

some internal fertilisation has been observed
- sperm package (spermatophore) is inserted into the female

Question 26

Anthrozoans (sea anemone, corals): Reproduction

Answer 26

• No medusa stage
• Some hermaphrodite
• Release gametes into water
• Go from polyp to adult form
• Copulation has been observed in one species
• Planula larva